1-Alkyl-1-methylpiperazine-1,4-diium salts: Synthetic, acid-base, XRD-analytical, FT-IR, FT-Raman spectral and quantum chemical study

Journal of Molecular Structure 1094 (2015) 210–236

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Journal of Molecular Structure

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1-Alkyl-1-methylpiperazine-1,4-diium salts: Synthetic, acid–base,

XRD-analytical, FT-IR, FT-Raman spectral and quantum chemical study

a

b

c,

b

⇑

ˇ

Dana Nemecková , Y. Sheena Mary , C. Yohannan Panicker , Hema Tresa Varghese ,

Christian Van Alsenoy ^d, Markéta Procházková ^a, Pavel Pazdera ^a, Abdulaziz A. Al-Saadi ^e

^aCentre for Syntheses at Sustainable Conditions and Their Management, Faculty of Science, Masaryk University, Brno, Czech Republic

^bDepartment of Physics, Fatima Mata National College, Kollam, Kerala, India

^cDepartment of Physics, TKM College of Arts and Science, Kollam, Kerala, India

^dStructural Chemistry Group, Department of Chemistry, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium

^eDepartment of Chemistry, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

ꢀ

Spectroscopies properties were

examined by FT-IR and FT-Raman

spectra.

ꢀ

The complete vibrational assignments

are made on the basis of Potential

energy distribution.

ꢀ

NBO analysis and HOMO and LUMO

energies are predicted.

Acid–base study was performed.

a r t i c l e i n f o

a b s t r a c t

Article history:

We report the preparation and results of vibrational spectral analysis, which were obtained using both

FT-IR and FT-Raman spectroscopy, for three 1-alkyl-1-methylpiperazine-1,4-diium salts (AMPSs), where

alkyl is benzyl 4a, n-octadecyl 4b, and methyl 4c, respectively. These were prepared by multistep synthe-

sis from piperazine. The acid–base study of AMPSs was performed and corresponding acid–base con-

stants were obtained. Single crystals of AMPSs suitable for XRD-analysis were obtained and analyzed.

The complete vibrational assignments of wavenumbers were made on the basis of a potential energy dis-

tribution. The HOMO and LUMO analysis was used to determine the charge transfer within the molecules.

The calculated ﬁrst hyperpolarizabilities of AMPSs 4a–4c are 48.34, 57.77 and 123.41 times that of urea.

As can be seen from the MEP plots, the negative electrostatic potential regions are mainly localized over

the chlorine and oxygen atoms for compounds 4a and 4b and chlorine and iodine atoms of compound 4c,

and are possible sites for electrophilic attack.

Received 14 February 2015

Received in revised form 13 March 2015

Accepted 24 March 2015

Available online 31 March 2015

Keywords:

DFT

Piperazinium salt

XRD-analysis

PED

Vibrational spectroscopy

Introduction

Piperazine quaternary salts have a broad application spectrum

ﬁrst of all as medicinal drugs or pro-drugs, as additives in

electrophoresis or ones with long chain on piperazinium nitrogen

⇑

Corresponding author. Tel.: +91 9895370968.

E-mail address: cyphyp@rediffmail.com (C.Y. Panicker).

as surfactants. For example, mono-quaternary piperazinium salts

http://dx.doi.org/10.1016/j.molstruc.2015.03.051

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

211

prepared from a number of N-benzyl-N⁰-alkylpiperazines were

tested for spasmolytic activity [1]. A number of piperazine quater-

nary salts were made for anthelmintic testing, some with an excel-

lent therapeutic index against Syphacia obvelata in the mouse [2]. A

novel class of piperazine quaternary salts was tested for activity

against certain nematode endoparasites such as ascaris and pin-

worms [3]. Mono-quaternary N,N-dimethylpiperazine and

di-quaternary N,N,N⁰-trimethylpiperazine derivatives of chitosan,

with different degrees of substitution, were investigated for anti-

bacterial activity against ﬁve strains of Gram-positive and Gram-

negative bacteria [4]. Quaternary piperazinium salts were patented

as pro-drugs in connection with parent piperazine structural

motive contained in drugs [5]. A series of long-chain piperazine

derivatives, N-alkyl-N⁰-methyl piperazine and their amphiphilic

salts, N-alkyl-N⁰-ethyl-N⁰-methylpiperazinium bromide, and the

related N-alkyl-N, N⁰-dimethylpiperazinium bromide were synthe-

sized and tested for surface activity [6]. The differential behavior of

ﬁve different mono- and di-quaternary piperazine salts, among the

18 investigated, in modulating the electro-endo-osmotic ﬂow and

analyte separations in capillary zone electrophoresis was observed

and evaluated successfully [7]. The piperazines or cyclizines are

generally considered as ethylenediamine derivatives or cyclic

ethylenediamines and are a broad class of chemical compounds

with many important pharmacological properties. The piper-

azine-based research has attracted considerable attention in recent

years. Piperazine and substituted piperazine nuclei had constituted

an attractive pharmacological scaffold present in various potent

marketed drugs. The incorporation of piperazine is an important

synthetic strategy in drug discovery due to its easy modiﬁability,

proper alkalinity, water solubility, the capacity for the formation

of hydrogen bonds and adjustment of molecular physicochemical

properties [8–11]. Piperazines have the chemical similarity with

piperidine, a constituent of piperazine in the black pepper plant.

Piperazine is introduced into medicine for better solubility of uric

acid crystals [12,13]. Recently, piperazine derivatives containing

tetrazole nucleus have been reported as an antifungal agent [14].

In particular, structurally simple 1-(1-naphthylmethyl)-piperazine,

as the efﬂux pump inhibitor, could exert positive effect on

tetracyclines and ciproﬂoxacin against their resistant bacteria

[15,16]. Moreover, benzotriazole-based piperazine derivatives

and N,N⁰-bis(alkyloxymethyl) piperazines had moderate antibac-

terial and antifungal activities against pathogenic bacterial strains

and fungal strains [17,18]. These results once again highlighted

that piperazine core was an important backbone and prompted

us to design some active molecules with piperazine nucleus. A

broad range of biological active compounds displaying antibacter-

ial [19–22], antifungal [23], anticancer [24–26], anti-parasitic

[27,28], anti-histamin [29], psychotolytic [30] and anti-depressive

activities [31] have been also found to contain this versatile core. In

the present work we report the protocol of title AMPSs multistep

synthesis, their acid–base behavior in comparison with another

piperazine derivatives, XRD analysis, theoretical and experimental

(IR and Raman) spectra along with NBO analysis. Therefore, the

aim of this study is fully determine the molecular structure, vibra-

tional modes and wavenumbers by quantum chemical calcula-

tions. Detailed interpretations of the vibrational spectra have

been made based on the potential energy distribution.

4-carbmethoxy-piperazine-1-ium chloride were purchased from

Tau-Chem Ltd. (Slovakia) [32]. The samples of title AMPSs prepared

and puriﬁed by crystallization as presented below were dried for

further experimental use at laboratory temperature and pressure

in a drying box ﬁlled by anhydrous calcium dichloride to constant

weigh. Melting points were determined on Boetius microscope

with digital thermometer and are not corrected. Potentiometric

titrations were done by using instrument Titroline Alpha Plus

(SCHOTT, Fischer Scientiﬁc) and electrode SenTix 21 (WTW) in a

water solution. X-ray crystal data and structure reﬁnement of

AMPSs were collected with a KUMA KM-4 kappa four-circle

diffractometer. The structure was solved by direct methods using

SHELXS86 [33] and reﬁned on F2 for all reﬂections using

SHELX193 [34]. Single crystal of 1-benzyl-1-methyl-piperazine-

1,4-diium dichloride monohydrate (4a), 1-methyl-1-octade-

cylpiperazine-1,4-diium dichloride monohydrate (4b), and

1,1-dimethylpiperazine-1,4-diium chloride iodide (4c) suitable

for XRD-analysis was obtained in the form of white prisms, 4a by

crystallization from isopropyl alcohol at room temperature, 4b

by diffusion of diethyl ether into the solution of 4b in DMF, 4c by

crystallization from ethanol at room temperature. The AMPSs crys-

tallographic data have been deposited with the Cambridge

Crystallographic Data Center as supplementary publications num-

ber CCDC 831892 (4a), 831894 (4b), and 831893 (4c), respectively.

The NMR spectra, both ¹H- and ¹³C NMR, were acquired on a

Bruker Avance 500/100 MHz spectrometer. Chemical shifts (d)

are reported in ppm. Gas chromatography was acquired at

Shimadzu GC-17A. MALDI TOF mass spectra were measured on

an AXIMA CFR mass spectrometer from Kratos Analytical Ltd.

(Manchester, United Kingdom) equipped with a nitrogen laser

wavelength of 337 nm from Laser Science Inc. of Franklin

(Franklin, MA, USA). 2,5-Dihydroxybenzoic acid (DHB) matrices

were tried for MALDI TOF measurement. Red phosphorus was used

for external calibration [35].

The FT-IR spectra (Figs. 1–3) of AMPSs 4a–4c were recorded

using Genesis (Unicam Mattson) spectrometer, measurement of

samples in potassium bromide pellets. The FT-Raman spectrum

(Figs. 4–6) was obtained on a Bruker, Equinox 55/s spectrometer

with FRA Raman socket, 106/s. For a excitation of the spectrum

the emission of the Nd:YAG laser was used, excitation wavelength

1064 nm, maximal power 500 mV, measurement of solid samples.

All the expanded experimental spectra are given in Figs. S1–S6 as

supporting materials.

Synthesis

4-Carbmethoxypiperazine-1-ium chloride (1)

Compound was prepared by the described procedure [36], i.e.

by reaction of methyl chloroformate with piperazine in acetic acid

solution at room temperature under catalysis by Cu(II) cation sup-

ported on weak acidic cation-exchanger of polyacrylic type, pre-

paration of catalyst in [37]. Yield, m.p. and other characteristics

agreed on described ones.

1-Benzyl-4-carbmethoxypiperazine (2a)

The mixture containing 1 (9.0 g, 50 mmol), benzyl chloride

(7.0 g, 55 mmol), 10 mol% of sodium iodide as catalyst, potassium

carbonate (13.8 g, 100 mmol) in 50 mL of DMF was heated at

80 °C over a period of 8 h. Reaction course was monitored by

TLC. Thereafter the mixture was cooled to room temperature,

solids were ﬁltered off by suction and DMF evaporated in vacuum.

The residuum was mixed with 20 mL of dry diethyl ether and solu-

tion was ﬁltered with 100 mg of silica gel. It was obtained 10.8 g

(92%) of 1-benzyl-4-carbmethoxypiperazine as yellowish syrup

liquid, Purity by GC 96.8%.

Experimental

General

All used chemicals for syntheses were purchased from Sigma–

Aldrich (Germany) in ACS reagent grade or ReagentPlus^Òand were

used without further puriﬁcation, catalyst, i.e. Cu(II) cation sup-

ported on weak acidic cation-exchanger of polyacrylic type, and

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

212

Fig. 1. FT-IR spectrum of 1-benzyl-1-methylpiperazine-1,4-diium dichloride

monohydrate (4a).

Fig. 3. FT-IR spectrum of 1,1-dimethylpiperazine-1,4-diium chloride iodide (4c).

¹H NMR (d⁶-acetone, TMS) d/ppm: 7.24–7.45 (5H, m, ArAH),

3.64 (3H, s, OCH₃), 3.54 (2H, s, CH₂of Bn), 3.43–3.46 (4H, m, CH₂

of piperazine), 2.38–2.42 (4H, m, CH₂of piperazine). ¹³C NMR

(d⁶-acetone, TMS) d/ppm: 157.72 (C@O), 138.48 (C_Ar), 126.97,

128.10, 130.77 (CH_Ar), 62.87 (CH₂of Bn), 53.00 (OACH₃), 46.45

(CH₂of piperazine), 44.06 (CH₂of piperazine). MS–M⁺

C₁₃H₁₈N₂O₂(Da, calc./found) 234.294/234.293.

2.33–2.41 (6H, m, CH₂of piperazine, CH₂C₁₇H₃₅), 1.23–1.28 (32H,

m, (CH₂)₁₆), 0.90 (3H, t, J = 6.58 Hz, CH₃). ¹³C NMR (CDCl₃, TMS)

d/ppm: 156.27 (C@O), 59.17 (CH₂C₁₇H₃₅), 53.32 (OACH₃), 52.89

(CH₂of piperazine), 44.11 (CH₂of piperazine), 32.31, 30.07,

29.74, 29.90, 23.07 ((CH₂)₁₆), 14.47 (CH₃). MS–M⁺C₂₄H₄₈N₂O₂

(Da, calc./found) 396.650/396.649.

1-Benzyl-4-carbmethoxy-1-methylpiperazine-1-ium iodide (3a)

The reaction mixture containing 2a (11.7 g, 50 mmol), methyl

iodide (14.2 g, 100 mmol) in 50 mL of nitromethane was heated

at 50 °C over a period of 4 h. Reaction course was monitored by

TLC. Thereafter the ½ of nitromethane volume was evaporated,

the mixture was cooled to room temperature and 20 mL of diethyl

ether was added. Yellowish solid was crystalized from isopropyl

alcohol. 1-Benzyl-4-carbmethoxy-1-methylpiperazinium iodide

(14.3 g, 76%) was obtained in the form of yellowish prisms. M.p.

196.6–198.3 °C. ¹H NMR (D₂O, TMS) d/ppm: 7.48–7.51 (5H, m,

ArAH), 4.61 (2H, s, CH₂of Bn), 3.45–4.09 (11H, m, CH₂of

1-Carbmethoxy-4-octadecylpiperazine (2b)

Compound 2b was synthetized according to above procedure

for 2a. Octadecyl bromide (18.3 g, 55 mmol) was used in lieu of

benzyl chloride and nitromethane (80 mL) as solvent. Reaction

temperature was 50 °C and time 10 h. Product crystalizing after

cooling of reaction mixture was separated by suction and puriﬁed

by crystallization from methanol (charcoal). It was prepared 15.7 g

(79%) of 1-carbmethoxy-4-octadecylpiperazine as a yellowish wax

solid. M.p. 41.3–43.9 °C, purity by GC 96.2%. ¹H NMR (CDCl₃, TMS)

d/ppm: 3.71 (3H, s, OCH₃), 3.48–3.54 (6H, m, CH₂of piperazine),

Fig. 2. FT-IR spectrum of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride

monohydrate (4b).

Fig. 4. FT-Raman spectrum of 1-benzyl-1-methylpiperazine-1,4-diium dichloride

monohydrate (4a).

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

213

(CDCl₃, TMS) d/ppm: 155.54 (C@O), 65.34 (CH₂C₁₇H₃₅), 59.99

(CH₂of piperazine), 59.17 (OACH₃), 53.86 (CH₂of piperazine),

48.09 (N⁺ACH₃), 38.45, 32.27, 30.07, 26.63, 23.04, 22.51

((CH₂)₁₆), 14.45 (CH₃). MS–M⁺C₂₅H₅₁N₂O₂(Da, calc./found)

411.685/411.684.

4-Carbmethoxy-1,1-dimethylpiperazine-1-ium iodide (3c)

The mixture containing 1 (9.0 g, 50 mmol), methyl iodide

(28.4 g, 200 mmol), and potassium carbonate (13.8 g, 100 mmol)

in 25 mL of nitromethane was heated at 50 °C over a period of

24 h. Reaction course was monitored by TLC. Thereafter the 1/3

of liquid volume was evaporated, the mixture was cooled to room

temperature and 20 mL of acetone was added. Yellowish solid was

crystalized

from

isopropyl

alcohol.

4-Carbmethoxy-1,1-

dimethylpiperazine-1-ium iodide (7.8 g, 52%) was obtained in the

form of yellowish prisms. M.p. 196.1–198.9 °C (decomp.). ¹H

NMR (D₂O, TMS) d/ppm: 3.65–3.92 (4H, m, CH₂of piperazine),

3.74 (3H, s, OACH₃), 3.47–3.60 (4H, m, CH₂of piperazine), 3.19

(6H, s, CH₃). ¹³C NMR (D₂O, TMS) d/ppm: 155.00 (C@O), 61.36

(CH₂of piperazine), 54.35 (OACH₃), 52.80 (CH₃), 38.49 (CH₂of

piperazine). MS–M⁺C₈H₇N₂O₂(Da, calc./found) 173.233/173.232.

Fig. 5. FT-Raman spectrum of 1-methyl-1-octadecylpiperazine-1,4-diium dichlo-

ride monohydrate (4b).

1-Benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a)

1-Benzyl-4-carbmethoxy-1-methylpiperazinium iodide (3.8 g,

10 mmol) was dissolved in 15 mL of water, next 15 mL of ethanol

and barium hydroxide octahydrate (3.3 g, 20 mmol) were added

and mixture was stirred at 80 °C for the duration of 30 h. The hot

reaction mixture was ﬁltered with a charcoal and solvents were

evaporated in vacuum. Solid residuum was mixed with 20 mL of

4 M methanol solution of hydrogen chloride and evaporated in

vacuum. The white rest was recrystallized from isopropyl alcohol.

1-Benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate

(2.3 g, 88%) was obtained in the form of white prisms. M.p.

172.1–173.9 °C (decomp.). Purity by potentiometric titration was

min. 98.2%. ¹H NMR (D₂O, TMS) d/ppm: 7.30–7.48 (5H, m, ArAH),

4.50 (2H, s, CH₂of Bn), 3.53–3.64 (8H, m, CH₂of piperazine),

2.95 (3H, s, CH₃). ¹³C NMR (D₂O, TMS) d/ppm: 133.48 (C_Ar),

125.52, 128.36, 131.62 (CH_Ar), 62.82 (CH₂of Bn), 55.97 (CH₂of

piperazine), 46.39 (CH₃), 38.05 (CH₂of piperazine). MS–M⁺

C₁₂H₁₉N₂(Da, calc./found) 191.293/191.292.

piperazine, OACH₃), 3.08 (3H, s, CH₃). ¹³C NMR (D₂O, TMS) d/ppm:

157.26 (C@O), 133.63 (C_Ar), 126.46, 129.23, 131.47 (CH_Ar), 69.36

(CH₂of Bn), 59.09 (CH₂of piperazine), 54.13 (OACH₃), 45.92

(CH₃), 38.08 (CH₂of piperazine). MS–M⁺C₁₄H₂₁N₂O₂(Da, calc./

found) 249.329/249.328.

4-Carbmethoxy-1-methyl-1-octadecylpiperazine-1-ium iodide (3b)

The compound was synthetized from 2b (19.8 g, 50 mmol)

according to above procedure for 3a. Reaction lasted for 3.5 h.

The hot reaction mixture was ﬁltered with a charcoal, a product

crystalizing after cooling to 5 °C was ﬁltered by suction. The

product was puriﬁed by the recrystallization from dioxane. It

was prepared 19.9 g (74%) of 4-carbmethoxy-1-methyl-1-octade-

cylpiperazine-1-ium iodide as yellowish prism. M.p. 148.7–

151.7 °C (decomp.). ¹H NMR (CDCl₃, TMS) d/ppm: 3.60–4.01

(13H, m, CH₂of piperazine + CH₂C₁₇H₃₅+ OCH₃), 3.48 (3H, s,

N⁺ACH₃), 2.33–2.41 (6H, m, CH₂of piperazine, CH₂C₁₇H₃₅), 1.23–

1.28 (32H, m, (CH₂)₁₆), 0.86 (3H, t, J = 6.58 Hz, CH₃). ¹³C NMR

1-Methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate

(4b)

This compound was synthetized from 4-carbmethoxy-1-

methyl-1-octadecylpiperazine-1-ium iodide (5.4 g, 10 mmol) by

procedure above described for preparation of 1-benzyl-1-methyl-

piperazine-1,4-diium dichloride monohydrate. Reaction time was

32 h. The hot reaction mixture was ﬁltered with a charcoal and ﬁl-

trate evaporated to dryness. The white solid was boiled with 20 mL

of 4 M methanol solution of hydrogen chloride, a product crys-

talizing after cooling to 5 °C was ﬁltered by suction and washed

by acetone. 1-Methyl-1-octadecyl piperazine-1,4-diium dichloride

monohydrate (3.4 g, 80%) was obtained in the form of yellowish

prisms. M.p. 78.8–83.5 °C (decomp.). Purity by potentiometric

titration was min. 97.6%. ¹H NMR (D₂O, TMS) d/ppm: 3.65–3.90

(10H, m, CH₂of piperazine + CH₂C₁₇H₃₅), 3.35 (3H, s, N⁺ACH₃),

1.29–1.38 (32H, m, (CH₂)₁₆), 0.87 (3H, t, J = 6.58 Hz, CH₃). ¹³C

NMR (CDCl₃, TMS) d/ppm: 61.39 (CH₂C₁₇H₃₅), 57.90 (CH₂of piper-

azine), 48.28 (N⁺ACH₃), 41.80 (CH₂of piperazine), 33.15, 32.17,

29.27, 25.85, 23.04, 20.15 ((CH₂)₁₆), 14.06 (CH₃). MS–M⁺

C₂₃H₄₉N₂(Da, calc./found) 353.649/353.648.

1,1-Dimethylpiperazine-1,4-diium chloride iodide (4c)

4-Carbmethoxy-1,1-dimethylpiperazine-1-ium iodide (3.0 g,

10 mmol) was dissolved in 15 mL of water, next 15 mL of ethanol

and barium hydroxide octahydrate (3.3 g, 20 mmol) were added

Fig. 6. FT-Raman spectrum of 1,1-dimethylpiperazine-1,4-diium chloride iodide

(4c).

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

214

and mixture was stirred at 80 °C for the duration of 30 h. The hot

reaction mixture was ﬁltered with a charcoal and solvents were

evaporated in vacuum. Solid residuum was mixed with 20 mL of

4 M methanol solution of hydrogen chloride and evaporated in

vacuum. The white rest was recrystallized from isopropyl alcohol.

1,1-Dimethylpiperazine-1,4-diium chloride iodide (1.7 g, 61%) was

obtained in the form of yellowish prisms. M.p. 196.9–202.0 °C

(decomp.). 1,1-Dimethylpiperazine-1,4-diium dichloride [38].

M.p. 216 °C (decomp., ethanol). Purity by potentiometric titration

was min. 98.4%. ¹H NMR (D₂O, TMS) d/ppm: 3.75–3.80 (8H, m,

CH₂of piperazine), 3.36 (6H, s, CH₃). ¹³C NMR (D₂O, TMS) d/ppm:

58.55 (CH₂of piperazine), 52.62 (CH₃), 38.38 (CH₂of piperazine).

MS–M⁺C₆H₁₅N₂(Da, calc./found) 115.197/115.196.

the anharmonicity and of the general tendency of the quantum

chemical methods to overestimate the force constants at the exact

equilibrium geometry. The optimized geometrical parameters with

XRD data are given in Tables 2–4. The potential energy distribution

(PED) is calculated with the help of GAR2PED software package

[45]. The assignments of the calculated wavenumbers are aided

by the animation option of GaussView program, which gives a

visual presentation of the vibrational modes [46].

Results and discussion

The goal of our work was a synthesis of suitable AMPSs for their

collective acid–base, XRD, FT-IR, FT-Raman spectral and quantum

chemical study. We expected that short methyl-, benzene-ring

containing benzyl- and long lipophilic octadecyl-substituent could

show different properties within the frame of collective study.

Acid–base properties

Acid–base constants of AMPSs 4a–4c were determined by using

of potentiometric titrations. Titrations of AMPSs (concentration

0.01 M) in protonated form and their re-titrations in a conjugated

deprotonated free bases, i.e. 1-alkyl-1-methylpiperazine-1-ium

salts (concentration 0.01 M), were done. All potentiometric titra-

tions were realized in aqueous environment under temperature

control (295 K) and potentiometric titration were repeated for

twelve times. Obtained data were statistically evaluated by

software Origin 8.1 and acid–base constants were graphically

determined from titration curves after their ﬁtting and differentiat-

ing. Scheme 1 presents deprotonation/protonation equilibria of

AMPSs, found acid–base constants for all tree AMPSs and for

comparison also for piperazine-, 1-(pyrid-4-yl)piperazine [39],

Synthesis

The title AMPSs 4a–4c were synthesized from piperazine as the

starting compound. In view of the impossibility of direct mono-

quaternization of piperazine molecule, whereas an excess of an

alkylating agent yields either 1,4-dialkylpiperazine or its mixture

with mono- or di-quaternary piperazine salt, we use the synthetic

strategy via mono-protected piperazine. The introduction of benzyl

or similar protective group on N¹, i.e. 1-benzylpiperazine applica-

tion, is for the following synthetic steps the same problem as above

– formation of mono- and di-quaternized product mixtures on both

piperazine nitrogen atoms. On the other hand, mono-acylation or

similar protection such as a carbalkoxylation of piperazine mole-

cule at nitrogen N¹by electron-withdrawing substituent of an acyl

type followed by selective alkylation of N⁴and next by its

quaternization using methylating agent in the last alkylation step

could be suitable method for AMPSs synthesis. The ﬁnal step of syn-

thesis is a deprotection of acylated N¹in the molecule of an inter-

mediary product by simple cleavage method. N¹-mono-protection

of piperazine by an acylation or similar reaction, preparation of car-

bamates is for many reasons favorable, can be connected very often

with a formation of product mixtures, which contain 1-substituted

and 1,4-disubstituted piperazines. This fact, expensiveness of di-

tert-butyl dicarbonate and next a possibility for a cleavage of tert-

butoxycarbonyl (Boc) protective group in the course of piperazine

alkylation/quaternization by action of in situ formed acid such as

hydrogen halogenide, exclude an application of Boc as the protec-

tive group. However, we found the reaction condition for a direct

effective introduction of carbmethoxy group by simple method,

i.e. by reaction of methyl chloroformate with piperazine-1-ium

cation formed in situ in an acetic acid solution [47]. Because a

reactivity of piperazine-1-ium cation in comparison with piper-

azine is lower, the synthesis was catalyzed by Cu(II) cation sup-

ported on weak acidic cation-exchanger of a polyacrylic resin.

The second step of the synthesis, see Scheme 2, includes an

alkylation reaction of 4-carbmethoxypiperazine-1-ium chloride in

the presence of potassium carbonate as a base with benzyl chloride

in DMF, with octadecyl bromide or methyl iodide in nitromethane

and corresponding 1-alkyl-4-carbmethoxypiperazines (alkyl is

benzyl and octadecyl) were obtained. In the case of a methylation

reaction the all synthetic process was performed with an excess of

methyl iodide as a quaternization agent and 4-carbmethoxy-

1,1-dimethylpiperazine-1-ium iodide was prepared and identiﬁed.

Both 1-alkyl-4-carbmethoxypiperazines were quaternized in

the third synthetic step by action of methyl iodide in

nitromethane solution and corresponding 1-alkyl-4-carb-

methoxy-1-methylpiperazinium iodides were isolated. The last

step, i.e. cleavage of protective carbmethoxy-group, was realized

by barium hydroxide octahydrate according to described idea

4-methylpiperazine-,

4-ethylpiperazine-1-ium

salts

[40],

4-acetylpiperazine-, 4-benzoylpiperazine, and 4-tosylpiperazine-

1-ium cation [41] are presented as pK_A/pK_Bvalues in Table 1.

Values of logP were calculated using ACD/logP DB software [42].

Computational details

Calculations of the title compounds (4a–4c) were carried out

using Gaussian 09 software [43] by utilizing Becke’s three parame-

ter hybrid model with the Lee–Yang–Parr correlation functional

(B3LYP) method. The 6-311++G(d,p) (5D, 7F) basis set was

employed to predict the molecular structure and vibrational

wavenumbers. Molecular geometries were fully optimized by

Berny’s optimization algorithm using redundant internal coordi-

nates. Harmonic vibrational wavenumbers were calculated using

analytic second derivatives to conﬁrm the convergence to minima

on the potential surface. Then frequency calculations were

employed to conﬁrm the structure as minimum points in energy.

At the optimized structures (Figs. 7–9) of the examined species,

no imaginary wavenumber modes were obtained, proving that a

true minimum on the potential surface was found. The DFT method

tends to over-estimate the fundamental modes; therefore scaling

factor (0.9613) has to be used for obtaining a considerably better

agreement with experimental data [44]. The observed disagree-

ment between theory and experiment could be a consequence of

Scheme 1. Deprotonation/protonation equilibria of AMPSs 4a–4c.

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

215

Table 1

Values of pK_A/pK_Band partition coefﬁcient logP as a lipophilicity demonstration criterion for AMPSs 4a–4c and any of the other 1-substituted piperazines.

Piperazine-4-ium cation

4a

4b

4c

1-H

1-Me

1-Et

9.21

1-Py-4

1-Ac

1-Benzoyl

1-Tos^a

pK_A

4.99

0.04

4.02

0.04

4.89

0.04

9.61

0.04

9.14

0.03

8.99

0.03

7.94

–

7.78

–

7.39

–

0.02

pK_B

9.01

9.98

9.11

4.39

4.86

4.79

5.01

6.06

6.22

6.61

logP

ꢁ16.9

+3.17

0.50

ꢁ2.98

ꢁ1.7

ꢁ0.18

+0.35

0.32

+0.21

0.48

ꢁ0.77

ꢁ0.14

+1.57

0.38

0.51

0.50

0.29

0.32

0.43

0.47

a

Me – methyl; Et – ethyl; Py – 4-pyrid-4-yl; Ac – acetyl; Tos – 4-toluenesulfonyl.

Fig. 7. Optimized geometry (B3LYP/6-311++G(d,p) (5D, 7F)) of 1-benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a).

Fig. 8. Optimized geometry (B3LYP/6-311++G(d,p) (5D, 7F)) of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

[48] in ethanol and after a processing of reaction mixture the ﬁnal

AMPSs 4a–4c were isolated in good yield and identiﬁed as

described in the experimental part Section Synthesis. The prepared

AMPSs 4a–4c and their synthetized precursors 2a, 2b and 3a–3c, as

are described and identiﬁed in this work, are not described till

now.

1-ium salts in the water solution depends as on an electronegativ-

ity/partial charge of substituted atom N⁴as that on a lipophilicity

of substituent(s) presented on this nitrogen. The calculated/esti-

mated values of partition coefﬁcient logP as an auxiliary lipophilic-

ity demonstration criterion for AMPSs 4a–4c is presented in

Table 1, as well.

Electronegativity of N⁴affects electron density and namely

positive charge on N¹and herewith its acidity, i.e. an ability of pro-

ton coordination/de-coordination. Non-substituted piperazine-1-

ium cation is the less acidic of all presented those according to

its pK_Avalue (Table 1). Ethyl and methyl substituents are elec-

tron-donors and appropriate piperazine-1-ium cations should be

Acid–base properties

The pK_Avalues of AMPSs 4a–4c in the context with the next

1-mono-protonated 4-substituted piperazines demonstrated in

Table 1 shows that acidity of presented 4-substituted piperazine-

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

216

short contact with hydrogen in N⁺H₂piperazine (strong ion–dipole

interaction) or with hydrogen of both piperazine methylene CH₂.

On the other hand, the iodide anions ensure selectively short con-

tacts with hydrogens of piperazine methylenes or hydrogens of

methyl groups, as well. Further parameters characterizing the

individual molecules of AMPSs 4a–4c such as bond lengths, bond

angles, and dihedral angles are discussed in comparison with com-

puted those below.

IR and Raman spectra

The calculated (scaled) wavenumbers, observed IR, Raman

bands and assignments of compounds 4a, 4b and 4c, respectively,

are given in Tables 5–7.

Fig. 9. Optimized geometry (B3LYP/6-311++G(d,p) (5D, 7F)) of 1,1-dimethylpiper-

azine-1,4-diium chloride iodide (4c).

1-Benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a)

In the following discussion, phenyl and piperazine rings are

designated as Ph and Pz respectively. The stretching vibrations of

the CH₃group are expected in the range of 2900–3050 cm^ꢁ1

[51,52]. The antisymmetric stretching modes of the methyl group

are calculated to be at 3053, 3047 cm^ꢁ1and the symmetric modes

at 2961 cm^ꢁ1. The antisymmetric and symmetric bending vibra-

tions of the methyl group normally appear in the region of 1400–

1485 cm^ꢁ1and 1380–1420 cm^ꢁ1[51,53]. The band observed at

1438 cm^ꢁ1in the Raman spectrum is assigned as CH₃bending

mode. The B3LYP calculations give these modes at 1447, 1435,

1403 cm^ꢁ1. In the present case, the rocking modes of methyl group

were calculated to be at 1122, 1117 cm^ꢁ1and observed at

1096 cm^ꢁ1in the IR spectrum. The torsion vibrations of methyl

groups were often assigned within the region 185 65 cm^ꢁ1[51].

The CC modes are also identiﬁed and assigned (Table 5).

less acidic than single piperazine-1-ium cation, which is not true.

This discrepancy is evoked by a worse solvation of these alkylated

cations than single piperazine-1-ium cation, probably. On the other

hand, acyl-, benzoyl- and 4-toluenesulfonyl-substituents are elec-

tron-withdrawing groups which by the mentioned way increase

acidity of corresponding substituted piperazine-1-ium, 4-

toluenesulfonyl mostly, because strong electron-withdrawing and

lipophilic group, acetyl group at the least. Within this context,

the AMPSs 4a–4c are the strongest acids and the highest acidity

of octadecyl salt is given by presence of high lipophilic octadecyl

substituent which is very bad solvated in water environment.

XRD analysis

The methylene vibrations are expected in the regions 2900–

3000 cm^ꢁ1(stretching modes), 1100–1450 cm^ꢁ1(scissoring, wag-

ging and twisting modes) [51,52]. The stretching modes of the

CH₂are assigned at 3015, 2957 cm^ꢁ1(theoretically). The deforma-

tion modes of the CH₂group are assigned at 1421, 1318, 1241 cm^ꢁ1

theoretically and at 1321 cm^ꢁ1in the IR spectrum. The rocking

modes of the CH₂group appear in the region [51] 875 25 cm^ꢁ1

and for the title compound the band at 891 (IR), 888 (Raman)

and 886 cm^ꢁ1(DFT) are assigned as rocking mode theoretically.

The NH₂antisymmetric stretching vibrations [51] give rise to a

strong band in the region 3390 60 cm^ꢁ1and the symmetric NH₂

stretching in the region 3210 60 cm^ꢁ1with a somewhat weaker

intensity. The DFT calculations give these modes at 3303 and

3266 cm^ꢁ1as antisymmetric and symmetric NH₂stretching

modes. The bands observed at 3343 and 3181 cm^ꢁ1in the IR spec-

trum are assigned as NH₂stretching mode for the title compound.

The NH₂deformation band [51] d(NH₂) is expected in the region

1610 30 cm^ꢁ1. For the title compound, d(NH₂) band is observed

at 1590 cm^ꢁ1in the IR spectrum and at 1594 cm^ꢁ1theoretically.

Compounds 4a and 4b were analyzed in the form of dichloride

monohydrate, compound 3 as chloride iodide. XRD-analysis all tree

molecules shown that piperazine skeleton is in stable chair con-

formation, its four carbon atom are in plain and both nitrogen atom

are in apexes of molecule. In the cases 4a and 4b occupy the bulki-

est substituents on nitrogen atom, i.e. benzyl and octadecyl, the

equatorial position. These observations are in accord with

fundamental knowledge about conformation of substituted cyclo-

hexane and hetero-cyclohexane rings [49,50].

The molecular packing diagrams of compounds 4a–4c are

shown in Figs. 10–12. A molecular packing in a cell of AMPSs 4a–

4c shows that chloride/iodide anion in connection with water

molecule, if this is presented, ensures binding between two and

more molecules of AMPS. This binding is realized in molecular

net of 4a by short contacts between both water hydrogen atoms

and the chloride anion and next by short contact between this

anion and both nitrogen and hydrogen atoms of N⁺H₂. Oxygen

atom of water molecule is in contact with hydrogen atoms of the

presented phenyl ring, CH₂in piperazine and CH₃in methyl,

respectively. Short contacts between oxygen of water and speciﬁed

hydrogen atom above, as well as between carbon and hydrogen

atom neighboring molecules, realize molecular net, as well. On

the other hand, geometry of phenyl ring in benzyl groups, which

are not in crystal parallel, allows not stacking through these rings.

A molecular net in the crystal of 4b, with the exception of par-

ticipation of absent benzyl, is realized analogous to 4a. However,

the molecular packing shows further that rigid linear octadecyl

chain is on an all its size bonded with chain of next molecule in

a way head–tail conﬁguration by intermolecular short contact

CAH, i.e. by the weak lipophilic interactions between two long

parafﬁnic chains. The linearity of octadecyl chains is energy-pre-

ferred over its globular ordering.

The in-plane NH₂rock absorbs in the region [51] 1250 45 cm^ꢁ1

.

The band at 1378 (IR), 1377 (DFT) are assigned to rocking mode

of NH₂for the title compound. The amide band, absorbing in the

region 775 45 cm^ꢁ1is assigned to NH₂out-of-plane twist and

wagging mode of NH₂is expected in the region 670 60 cm^ꢁ1

[51]. The NH₂wag is usually clearly separated from the twist and

is easy to recognize by its broad band structure. The out-of-plane

NH₂twist is observed at 842 cm^ꢁ1in the Raman spectrum and at

845 cm^ꢁ1theoretically. The wagging mode of NH₂is observed at

718 cm^ꢁ1in the IR spectrum and at 721 cm^ꢁ1theoretically for

the title compound.

El-Emam et al. [54] reported the antisymmetric stretching CH₂

vibrations in the piperazine ring in the range 3033–2966 cm^ꢁ1

,

while the symmetric vibrations lying in the range 2874–

2834 cm^ꢁ1. For the title compound the bands at 3024, 3022,

3012, 3007 and 2972, 2970, 2954, 2951 cm^ꢁ1(DFT) are assigned

A molecular stacking in the crystal of 4c demonstrate that chlo-

ride anions bond the second and next molecules of 4c by their

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D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

217

Table 2

Optimized (DFT) geometrical parameters (DFT/XRD) of 1-Benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a).

Label

DFT(XRD)

Label

DFT(XRD)

Bond lengths (Å)

N1AC3

N1AC15

N2AC6

N2AH33

C3AH4

C3AC6

1.5084(1.5016)

1.5503(1.5310)

1.4880(1.4930)

1.0189(1.0160)

1.0891(0.9900)

1.5250(1.5140)

1.0913(0.9900)

1.0910(0.9900)

1.0940(0.9900)

1.0907(0.9900)

1.5041(1.5080)

1.4015(1.3930)

1.3931(1.3930)

1.3941(1.3800)

1.3943(1.3840)

1.3927(1.3880)

1.0855(0.9800)

1.0878(0.9800)

N1AC12

N1AC29

N2AC9

N2AH34

C3AH5

1.5264(1.5130)

1.5093(1.5010)

1.4955(1.4880)

1.1639(0.9420)

1.0916(0.9900)

1.0911(0.9900)

1.0908(0.9900)

1.5176(1.5100)

1.0908(0.9900)

1.0930(0.9900)

1.4009(1.3890)

1.0854(0.9500)

1.0840(0.9500)

1.0841(0.9500)

1.0839(0.9500)

1.0855(0.9500)

1.0921(0.9800)

C6AH7

C6AH8

C9AH10

C9AC12

C12AH14

C15AH17

C18AC19

C19AH20

C21AH22

C23AH24

C25AH26

C27AH28

C29AH31

C9AH11

C12AH13

C15AH16

C15AC18

C18AC27

C19AC21

C21AC23

C23AC25

C25AC27

C29AH30

C29AH32

Bond angles (°)

C3AN1AC12

C3AN1AC29

C12AN1AC29

C6AN2AC9

C6AN2AH34

C9AN2AH34

N1AC3AH4

108.4(108.5)

111.0

111.7(110.3)

112.6(110.2)

106.3

C3AN1AC15

110.7

105.3

109.6(109.4)

110.4

C12AN1AC15

C15AN1AC29

C6AN2AH33

C9AN2AH33

H33AN2AH34

N1AC3AH5

109.6

108.1

107.3

107.5

N1AC3AC6

H4AC3AC6

112.4(112.6)

110.2

H4AC3AH5

H5AC3AC6

109.7

108.9

N2AC6AC3

N2AC6AH8

109.6(110.5)

109.9

N2AC6AH7

C3AC6AH7

107.8

108.1

C3AC6AH8

112.5

H7AC6AH8

108.9

N2AC9AH10

N2AC9AC12

H10AC9AC12

N1AC12AC9

N1AC12AH14

C9AC12AH14

N1AC15AH16

N1AC15AC18

H16AC15AC18

C15AC18AC19

C19AC18AC27

C18AC19AC21

C19AC21AH22

H22AC21AC23

C21AC23AC25

C23AC25AH26

H26AC25AC27

C18AC27AH28

N1AC29AH30

N1AC29AH32

H30AC29AH32

111.2

110.1

112.0

113.0(112.9)

105.9

110.0

104.9

114.4115.5

111.5

121.3

119.1(118.8)

120.5(120.7)

119.9

120.2

119.9(119.9)

120.1

119.7

119.4

110.1

108.1

N2AC9AH11

H10AC9AH11

H11AC9AC12

N1AC12AH13

C9AC12AH13

H13AC12AH14

N1AC15AH17

H16AC15AH17

H17AC15AC18

C15AC18AC27

C18AC19AH20

H20AC19AC21

C19AC21AC23

C21AC23AH24

H24AC23AC25

C23AC25AC27

C18AC27AC25

C25AC27AH28

N1AC29AH31

H30AC29AH31

H31AC29AH32

107.6

108.0

107.7

106.6

110.9

110.3

103.7

109.9

111.0

119.5

120.0

119.4

119.9(119.9)

120.0

120.1

120.2(120.3)

120.3

107.5

108.6

111.7

110.8

Dihedral angles (°)

C12AN1AC3AC6

C29AN1AC3AC6

C15AN1AC12AC9

C3AN1AC15AC18

C29AN1AC15AC18

C6AN2AC9AC12

N2AC9AC12AN1

N1AC15AC18AC27

C27AC18AC19AC21

C19AC18AC27AC25

C19AC21AC23AC25

ꢁ55.9(ꢁ53.8)

67.2(68.0)

173.3(173.4)

ꢁ68.1(ꢁ62.9)

54.7(60.3)

C15AN1AC3AC6

C3AN1AC12AC9

C29AN1AC12AC9

C12AN1AC15AC18

C9AN2AC6AC3

ꢁ170.9(ꢁ170.2)

54.7(54.2)

ꢁ67.9(ꢁ68.0)

174.9(179.4)

ꢁ56.9(ꢁ63.0)

57.7(57.1)

55.7(58.2)

N1AC3AC6AN2

ꢁ54.8(ꢁ65.8)

ꢁ94.8(ꢁ95.0)

1.6(1.1)

N1AC15AC18AC19

C15AC18AC19AC21

C15AC18AC27AC25

C18AC19AC21AC23

C21AC23AC25AC27

88.8(95.0)

178.0(177.3)

ꢁ177.9(ꢁ177.3)

ꢁ0.5(ꢁ0.8)

ꢁ1.5(ꢁ0.8)

ꢁ0.6(ꢁ0.7)

0.7(ꢁ0.8)

as CH₂antisymmetric and symmetric stretching modes. The bands

observed at 3020, 2994, 2920 in the IR spectrum and at 2972,

2930 cm^ꢁ1in the Raman spectrum are assigned as CH₂stretching

modes of the piperazine ring. The CH₂deformation modes of the

title compound are observed at 1452, 1425 cm^ꢁ1in the IR

spectrum and the scissoring and wagging modes are assigned in

the region 1433–1456 and 1366–1427 cm^ꢁ1theoretically. El-

Emam et al. [54] reported the vibrations of CH₂groups in the piper-

azine ring (the scissoring vibration and wagging vibration) in the

range 1457–1422 and 1379–1344 cm^ꢁ1respectively. In a study

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

218

Table 3

Optimized geometrical parameters of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

Label

DFT(XRD)

Label

DFT(XRD)

Bond lengths (Å)

N1AC3

N1AC15

1.5163(1.5062)

1.5129(1.5042)

1.5165(1.4872)

1.0272

1.089

1.5243(1.5042)

1.0901

N1AC12

N1AC19

N2AC9

N2AH75

C34AH36

C67AH68

C9AH10

1.5186(1.5042)

1.5648(1.4656)

1.5163(1.4772)

1.0269

1.0928

1.0911

1.0899

1.5248(1.5013)

1.0906

N2AC6

N2AH74

C34AH35

C3AC6

C67AH69

C9AH11

1.0912

1.0924

C9AC12

C12AH13

C15AH16

C15AH18

C19AH21

C22AH23

C22AC25

C25AH27

C28AH29

C28AC31

C31AH33

C34AH35

C34AC37

C37AH39

C40AH41

C40AC43

C43AH45

C46AH47

C46AC49

C49AH51

C52AH53

C52AC55

C55AH57

C58AH59

C58AC61

C61AH63

C64AH65

C64AC67

C67AH69

C70AH71

C70AH73

C12AH14

C15AH17

C19AH20

C19AC22

C22AH24

C25AH26

C25AC28

C28AH30

C31AH32

C31AC34

C34AH36

C37AH38

C37AC40

C40AH42

C43AH44

C43AC46

C46AH48

C49AH50

C49AC52

C52AH54

C55AH56

C55AC58

C58AH60

C61AH62

C61AC64

C64AH66

C67AH68

C67AC70

C70AH72

1.0874

1.0867

1.0921

1.0946

1.5457(1.5285)

1.096

1.0969

1.5339(1.5204)

1.0971

1.0974

1.5333(1.5224)

1.0973

1.0975

1.5331(1.5354)

1.0975

1.0976

1.5330(1.5314)

1.0976

1.5330(1.5254)

1.0976

1.0977

1.089

1.0918

1.5218(1.5348)

1.0933

1.0962

1.5351(1.5275)

1.097

1.5337(1.5245)

1.0973

1.0974

1.5332(1.5205)

1.0976

1.5330(1.5214)

1.0977

1.5330(1.5184)

1.0977

1.53290(1.5195)

1.0978

1.5330(1.5194)

1.0977

1.0979

1.5330(1.5204)

1.0969

1.0933

1.53270(1.5214)

1.0978

1.0968

1.53140(1.5265)

1.0946

Bond angles (°)

C3AN1AC12

C3AN1AC19

C12AN1AC19

C6AN2AC9

C6AN2AH75

C9AN2AH75

N1AC3AH4

108.3(107.2)

109.4(117.1

107.0(98.2)

111.4(110.6)

109.7

C3AN1AC15

111.9(111.5)

111.1(111.9)

109.1(110.3)

110.1

110.2

105.6

C12AN1AC15

C15AN1AC19

C6AN2AH74

C9AN2AH74

H74AN2AH75

N1AC3AH5

109.7

108.5

106.8

N1AC3AC6

H4AC3AC6

113.9(113.4)

108.8

H4AC3AH5

H5AC3AC6

107.7

111.0

N2AC6AC3

N2AC6AH8

110.7(110.5)

106.8

N2AC6AH7

N3AC6AH7

108.2

109.5

N3AC6AH8

113.2

H7AC6AH8

108.2

N2AC9AH10

N2AC9AC12

H10AC9AC12

N1AC12AC9

N1AC12AH14

C9AC12AH14

N1AC15AH16

N1AC15AH18

H16AC15AH18

N1AC19AH20

N1AC19AC22

H20AC19AC22

C19AC22AH23

C19AC22AC25

H23AC22AC25

C22AC25AH26

C22AC25AC28

H26AC25AC28

C25AC28AH29

C25AC28AC31

H29AC28AC31

106.8

110.6(110.8)

113.4

114.3(112.9)

108.2

108.9

110.8

108.9

109.5

104.4

116.4(121.7)

111.2

111.3

109.4(111.1)

108.5

109.5

112.2(112.3)

109.5

109.3

112.8(114.6)

109.3

N2AC9AH11

H10AC9AH11

H11AC9AC12

N1AC12AH13

C9AC12AH13

H13AC12AH14

N1AC15AH17

H16AC15AH17

H17AC15AH18

N1AC19AH21

H20AC19AH21

H21AC19AC22

C19AC22AH24

H23AC22AH24

H24AC22AC25

C22AC25AH27

H26AC25AH27

H27AC25AC28

C25AC28AH30

H29AC28AH30

H30AC28AC31

108.3

108.1

109.5

106.8

110.7

107.6

108.3

109.6

109.7

105.0

108.4

110.9

111.3

107.9

108.5

109.3

106.8

109.5

109.3

106.5

109.4

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

219

Table 3 (continued)

Label

DFT(XRD)

Label

DFT(XRD)

C28AC31AH32

C28AC31AC34

H32AC31AC34

C31AC34AH35

C31AC34AC37

H35AC34AC37

C34AC37AH38

C34AC37AC40

H38AC37AC40

C37AC40AH41

C37AC40AC43

H41AC40AC43

C40AC43AH44

C40AC43AC46

H44AC43AC46

C43AC46AH47

C43AC46AC49

H47AC46AC49

C46AC49AH50

C46AC49AC52

H50AC49AC52

C49AC52AH53

C49AC52AC55

H53AC52AC55

C52AC55AH56

C52AC55AC58

H56AC55AC58

C55AC58AH59

C55AC58AC61

H59AC58AC61

C58AC61AH62

C58AC61AC64

H62AC61AC64

C61AC64AH65

C61AC64AC67

H65AC64AC67

C64AC67AH68

C64AC67AC70

H68AC67AC70

C67AC70AH71

C67AC70AH73

H71AC70AH73

109.2

113.1(113.2)

109.3

113.3(114.5)

109.2

109.3

113.4(113.80

109.3

113.5(114.4)

109.3

113.5(113.8)

109.3

113.5(113.8)

109.3

113.6(114.1)

109.2

109.3

113.6(114.1)

109.2

113.6(114.3)

109.2

113.6(114.2)

109.2

113.6(114.0)

109.2

109.3

113.7(114.5)

109.1

109.2

113.3(113.3)

109.5

111.4

111.2

C28AC31AH33

H32AC31AH33

H33AC31AC34

C31AC34AH36

H35AC34AH36

H36AC34AC37

C34AC37AH39

H38AC37AH39

H39AC37AC40

C37AC40AH42

H41AC40AH42

H42AC40AC43

C40AC43AH45

H44AC43AH45

H45AC43AC46

C43AC46AH48

H47AC46AH48

H48AC46AC49

C46AC49AH51

H50AC49AH51

H51AC49AC52

C49AC52AH54

H53AC52AH54

H54AC52AC55

C52AC55AH57

H56AC55AH57

H57AC55AC58

C55AC58AH60

H59AC58AH60

H60AC58AC61

C58AC61AH63

H62AC61AH63

H63AC61AC64

C61AC64AH66

H65AC64AH66

H66AC64AC67

C64AC67AH69

H68AC67AH69

H69AC67AC70

C67AC70AH72

H71AC70AH72

H72AC70AH73

109.3

106.3

109.3

106.2

109.3

109.2

106.1

109.3

109.2

106.1

109.2

106.1

109.2

106.1

109.2

106.1

109.2

106.0

109.2

106.0

109.2

106.0

109.2

106.0

109.2

109.3

106.0

109.1

109.2

106.1

109.4

111.2

107.6

107.5

107.6

Dihedral angles (°)

C12AN1AC3AC6

C19AN1AC3AC6

C15AN1AC12AC9

C3AN1AC19AC22

C15AN1AC19AC22

C6AN2AC9AC12

ꢁ53.8(ꢁ55.2)

ꢁ170.1(ꢁ164.1)

ꢁ69.6(ꢁ67.0)

ꢁ62.0(ꢁ65.6)

60.6(51.5)

C15AN1AC3AC6

C3AN1AC12AC9

C19AN1AC12AC9

C12AN1AC19AC22

C9AN2AC6AC3

69.0(67.6)

53.7(55.4)

171.5(177.1)

ꢁ179.1(ꢁ178.6)

ꢁ54.7(ꢁ56.0)

55.8(56.9)

54.3(56.8)

N1AC3AC6AN2

N2AC9AC12AN1

ꢁ55.2(ꢁ58.1)

ꢁ179.5(ꢁ169.1)

ꢁ179.5(ꢁ168.3)

ꢁ179.8(ꢁ178.9)

ꢁ179.8(ꢁ179.4)

ꢁ179.9(ꢁ179.8)

ꢁ180.0(ꢁ179.9)

ꢁ179.9(ꢁ179.6)

N1AC19AC22AC25

C22AC25AC28AC31

C28AC31AC34AC37

C34AC37AC40AC43

C40AC43AC46AC49

C46AC49AC52AC55

C52AC55AC58AC61

C58AC61AC64AC67

ꢁ179.8(167.4)

ꢁ179.1(177.6)

ꢁ179.2(178.7)

ꢁ179.3(171.3)

ꢁ179.4(ꢁ179.8)

ꢁ179.6(ꢁ179.9)

ꢁ179.7(ꢁ179.8)

ꢁ179.9(ꢁ179.9)

C19AC22AC25AC28

C25AC28AC31AC34

C31AC34AC37AC40

C37AC40AC43AC46

C43AC46AC49AC52

C49AC52AC55AC58

C55AC58AC61AC64

C61AC64AC67AC70

on the determination of piperazine rings in ethyleneamines,

poly(ethyleneamine) and polyethylenimine by infrared spectrome-

try, Spell reported that the piperazine ring was found to be asso-

compound the twisting vibrations are observed at 1289 cm^ꢁ1in

the Raman spectrum and at 1342, 1292, 1284, 1180 cm^ꢁ1theoreti-

cally. The rocking deformations are observed at 982 cm^ꢁ1in the

Raman spectrum and at 1153, 985, 977, 777 cm^ꢁ1theoretically

and these modes are not pure, but contain signiﬁcant contributions

from other modes also. El-Emam et al. [54] reported the CAN

stretching vibrations in the region 1154–756 cm^ꢁ1. For the title

compound CAN stretching vibrations are found at 1011,

884 cm^ꢁ1in the IR spectrum and at 1184, 1013, 848, 777 cm^ꢁ1

theoretically. Two absorptions characteristic for the piperazine

ring, at 1130 and 1168 cm^ꢁ1and assigned for the CAN stretching

vibrational modes were observed by da Silva et al. [56]. The shift

ciated with sharp, well-deﬁned absorptions at 1300–1345 cm^ꢁ1

,

1125–1170 cm^ꢁ1, 1010–1025 cm^ꢁ1and 915–940 cm^ꢁ1regions of

the IR spectrum [55]. A very sharp and intense band was observed

at 1037 cm^ꢁ1by da Silva et al. and was assigned to the ring CH₂

rocking motions [56]. As stated by Spell [55] this is one of the most

useful bands for detecting the presence of di-substituted piper-

azines. The twisting and rocking vibrations of the CH₂group

appear in the region [51] of 1200–1280 and 740–900 cm^ꢁ1, respec-

tively. These modes are also assigned (Table 5). For the title

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

220

compound these vibrations are observed at 1007, 773 cm^ꢁ1

theoretically.

Table 4

Optimized geometrical parameters of 1,1-dimethylpiperazine-1,4-diium chloride

iodide (4c).

Aromatic compounds commonly exhibit multiple weak bands

in the region 3100–3000 cm^ꢁ1, due to aromatic CH stretching

vibrations [51]. However, these bands are rarely useful because

they overlap with one another resulting in stronger absorption in

this region. The DFT calculations give the CH stretching modes of

the phenyl rings in the range 3033–3083 cm^ꢁ1for PhI(mono).

The band observed at 3029 cm^ꢁ1in the Raman spectrum is

assigned as CH stretching mode of the phenyl ring. For the title

compound, the bands at 1304, 1163, 1096, 1078 (IR), 1165, 1060

(Raman) and 1309, 1164, 1152, 1117, 1074 cm^ꢁ1(DFT) are

assigned as the CH in-plane bending modes of the phenyl ring.

The CH out-of-plane deformations are expected below 1000 cm^ꢁ1

[51] and for the title compound, the DFT calculations give bands

Label

DFT(XRD)

Label

DFT(XRD)

Bond lengths (Å)

N3AC5

N3AC17

N4AC8

N4AH25

C5AH6

C5AC8

C8AH10

C11AH13

C14AH15

C17AH18

C17AH20

C21AH23

1.5271(1.512) N3AC14

1.5092(1.495) N3AC21

1.4747(1.463) N4AC11

1.7099(1.104) N4AH26

1.0991(0.99)

1.5229(1.531) C8AH9

1.0927(0.99)

1.0919(0.99)

1.0924(0.99)

1.0894(0.98)

1.0899(0.98)

1.0861(0.98)

1.518(1.5124)

1.5122(1.507)

1.4678(1.459)

0.788(1.0172)

1.0928(0.99)

1.0913(0.99)

1.093(0.99)

C5AH7

C11AH12

C11AC14

C14AH16

C17AH19

C21AH22

C21AH24

1.53(1.527)

1.0916(0.99)

1.0958(0.98)

1.0959(0.98)

1.0896(0.98)

at 992, 966, 916, 826, 753 as c(CH) modes. Experimentally bands

Bond angles (°)

C5AN3AC14

C5AN3AC21

C14AN3AC21

C8AN4AC11

C8AN4AH26

C11AN4AH26

N3AC5AH6

are observed at 971, 908 cm^ꢁ1in the IR spectrum.

109.1(108.7)

111.0(107.5)

111.4

112.0(112.0)

110.3

110.5

106.4

112.2(112.5)

112.8

113.5

108.3

111.3

108.1

113.5(109.6)

111.0

112.7(112.2)

107.5

111.3

108.6

108.4

C5AN3AC17

C14AN3AC17

C17AN3AC21

C8AN4AH25

C11AN4AH25

H25AN4AH26

N3AC5AH7

H6AC5AH7

H7AC5AC8

N4AC8AH9

C5AC8AH9

H9AC8AH10

N4AC11AH13

H12AC11AH13

H13AC11AC14

N3AC14AH15

C11AC14AH15

H15AC14AH16

N3AC17AH19

H18AC17AH19

H19AC17AH20

N3AC21AH23

H22AC21AH23

H23AC21AH24

108.2

The benzene ring possesses six ring stretching modes of which

the four with the highest wavenumbers occurring near 1600,

1580, 1490 and 1440 cm^ꢁ1are good group vibrations [51]. The

bands at 1567, 1556, 1465, 1428 1297 cm^ꢁ1(DFT), 1470 cm^ꢁ1(IR)

and 1463 cm^ꢁ1(Raman) are assigned as phenyl ring stretching

modes of PhI. These modes are expected in the region 1250–

1620 cm^ꢁ1[51]. The ﬁfth ring stretching vibration is active near

1315 65 cm^ꢁ1, a region that overlaps strongly with that of the

CH in-plane deformation. The sixth ring stretching vibration, or

the ring breathing mode, appears as a weak band near 1000 cm^ꢁ1

in mono-, 1,3-di-, and 1,3,5-trisubstituted benzenes [51]. In the

otherwise substituted benzenes, however, this vibration is sub-

stituent sensitive and difﬁcult to distinguish from the ring in-plane

deformation [51]. The ring breathing mode of the mono substituted

benzene ring is assigned at 1006 cm^ꢁ1theoretically as expected.

109.5(107.8)

107.6(107.9)

111.2

105.6

107.0

105.7

108.8

110.7

109.0

108.2

106.3

109.1

106.4

108.4

106.3

110.4

108.4

N3AC5AC8

H6AC5AC8

N4AC8AC5

N4AC8AH10

C5AC8AH10

N4AC11AH12

N4AC11AC14

H12AC11AC14

N3AC14AC11

N3AC14AH16

C11AC14AH16

N3AC17AH18

N3AC17AH20

H18AC17AH20

N3AC21AH22

N3AC21AH24

H22AC21AH24

107.6

110.8

111.0

110.1

110.5

110.0

110.3

107.4

107.9

110.9

1-Methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate

(4b)

The stretching modes of the methyl group are calculated to be

in the range 2880–2966 cm^ꢁ1and 2964–3062 cm^ꢁ1for the methyl

groups attached with the CH₂chain and the piperazine ring.

Experimentally bands are observed at 3062 and 3054 cm^ꢁ1in the

Raman spectrum. The band observed at 1442, 1366 cm^ꢁ1in the

IR spectrum and 1440, 1358 cm^ꢁ1in the Raman spectrum ares

assigned as CH₃bending modes. The B3LYP calculations give these

modes in the ranges 1329–1452 cm^ꢁ1. In the present case, the

rocking modes of methyl group were calculated to be at 1159,

1100, 1098, 1075 cm^ꢁ1and observed at 1094 cm^ꢁ1in the IR spec-

trum and 1161, 1080 cm^ꢁ1in the Raman spectrum. The torsion

vibrations of methyl groups were often assigned within the region

Dihedral angles (°)

C14AN3AC5AC8

C21AN3AC5AC8

C17AN3AC14AC11 171.0(170.1)

C11AN4AC8AC5

N3AC5AC8AN4

ꢁ53.1(ꢁ54.5)

C17AN3AC5AC8

C5AN3AC14AC11

ꢁ172.3(ꢁ172.2)

70.0(69.3)

52.7(53.3)

C21AN3AC14AC11 ꢁ70.1(ꢁ71.0)

ꢁ52.0(ꢁ59.2)

C8AN4AC11AC14

N4AC11AC14AN3

51.3(58.5)

ꢁ53.2(ꢁ55.8)

54.0(57.6)

in the wavenumber may be attributed to the bulky groups attached

to the piperazine ring. The CAC stretching vibrations in the piper-

azine ring were reported at 972, 903 cm^ꢁ1[54]. For the title

Scheme 2. Synthetic pathway of title compounds 4a–4c.

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

221

444–1029 (rocking) cm^ꢁ1and observed at 1427, 1318, 1274,

1212, 1155, 1032, 830, 801, 721, 705, 441 in the IR spectrum and

at 1440, 1317, 1297, 1274, 1250, 1213, 1196, 1178, 1034, 828,

805, 719, 706, 441 cm^ꢁ1in the Raman spectrum. For the CH₂

groups, attached with the piperazine ring, deformation modes

are assigned in the ranges, 1428–1455, 1346–1399, 1181–1329

and 775–989 cm^ꢁ1theoretically. Experimentally bands are

observed at 1400, 775 cm^ꢁ1in the IR spectrum and 844 cm^ꢁ1in

the Raman spectrum for CH₂modes associated with the rings.

The DFT calculations give NH₂stretching modes at 3300 and

3258 cm^ꢁ1. The bands observed at 3454, 3382, 3185 cm^ꢁ1in the

IR spectrum and at 3316 cm^ꢁ1in the Raman spectrum are assigned

as NH₂stretching mode for the title compound. Here the NH₂

stretching mode splits into a doublet in the IR spectrum with a dif-

ference of 72 cm^ꢁ1and a shift of 82 cm^ꢁ1from the theoretical

value, which is due to the hydrogen bond with the neighboring

units. For the title compound, d(NH₂) band is observed at

1597 cm^ꢁ1in the IR spectrum, 1606 cm^ꢁ1in the Raman spectrum

and at 1595 cm^ꢁ1theoretically. The band at 1378 (IR), 1380

(Raman) and 1374 (DFT) is assigned to rocking mode of NH₂for

the title compound. The amide band, absorbing in the region

775 45 cm^ꢁ1is assigned to NH₂out-of-plane twist and wagging

mode of NH₂is expected in the region 670 60 cm^ꢁ1[51]. The

NH₂wag is usually clearly separated from the twist and is easy

to recognize by its broad band structure. The out-of-plane NH₂

twist is observed at 844 cm^ꢁ1in the Raman spectrum and at

847 cm^ꢁ1theoretically. The wagging mode of NH₂is assigned at

704 cm^ꢁ1theoretically for the title compound.

Fig. 10. Molecular packing of 1-benzyl-1-methylpiperazine-1,4-diium dichloride

monohydrate (4a) in a schematic view port. Carbon atoms, black, hydrogen atoms

gray, nitrogen blue, chloride anion green color. (For interpretation of the references

to color in this ﬁgure legend, the reader is referred to the web version of this

article.)

For the title compound, the piperazine ring stretching modes

are observed 1020, 1000, 801, 670 cm^ꢁ1in the IR spectrum,

1000, 673 cm^ꢁ1in the Raman spectrum and in the 673–

1019 cm^ꢁ1theoretically. The shift in the wavenumber may be

attributed to the bulky groups attached to the piperazine ring.

The CAN stretching vibrations are found at 917, 893 cm^ꢁ1in the

IR spectrum, 906, 890 cm^ꢁ1in the Raman spectrum and at 920,

900 cm^ꢁ1theoretically. For the title compound the CC stretching

vibrations of the CH₂chains are observed at 1051, 1020, 951,

935 cm^ꢁ1in the IR spectrum, 1080, 1050, 1023, 952, 930 cm^ꢁ1in

the Raman spectrum and in the range 935–1075 cm^ꢁ1theoreti-

cally. Most of the modes are not pure but contains signiﬁcant

contributions from other modes.

185 65 cm^ꢁ1[51]. The CC modes are also identiﬁed and assigned

(Table 6).

The stretching modes of the CH₂chains are assigned in the

range 2875–3002 cm^ꢁ1(theoretically) and bands are observed at

2997, 2916 cm^ꢁ1in the IR spectrum and at 3011, 2938 cm^ꢁ1in

the Raman spectrum whereas the CH₂modes attached with the

piperazine ring are assigned at 3021, 3012, 2980 cm^ꢁ1in the IR

spectrum, 3030, 2982, 2957 cm^ꢁ1in the Raman spectrum and in

the range 2952–3025 cm^ꢁ1theoretically. The deformation modes

of the CH₂groups (in the chain) are assigned in the ranges 1351–

1457 (scissoring), 1284–1347 (wagging), 1154–1279 (twisting),

Fig. 11. Molecular packing of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b) – a schematic viewport.

ˇ

222

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ

l

¼

ð

l_x²

þ

l_y²

þ

l_z²

a_zz

Þ

a_xx

þ

a_yy

þ

a₀

¼

3

The dipole moment

l, the mean polarizability a₀are calculated

using Gaussian 09 software and are found to be 3.878, 6.270,

5.612 Debye and 2.48 ꢂ 10^ꢁ23esu, 9.844 ꢂ 10^ꢁ23, 1.564 ꢂ 10^ꢁ23

,

for compounds 1, 2, 3, respectively. The ﬁrst order hyperpolarizabil-

ity b was also calculated using the ﬁnite ﬁeld approach theory. The

components of ﬁrst hyperpolarizability can be calculated using the

following equation:

X

1

3

b_i¼ b_ijk

þ

ðb_ijjþ b_jijþ b_jjiÞ; ði – jÞ

Using the x, y and z components, the magnitude of the ﬁrst

hyperpolarizability tensor can be calculated using

qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ

b_total

¼

ðb²_xþ b²_yþ b²_zÞ

Fig. 12. Molecular packing in 1,1-dimethylpiperazine-1,4-diium chloride iodide

(4c) – a schematic viewport. Iodide anions are in violet color. (For interpretation of

the references to color in this ﬁgure legend, the reader is referred to the web version

of this article.)

The complete equation for calculating the magnitude of the ﬁrst

hyperpolarizability from Gaussian 09 output is as follows.

b_x¼ b_xxxþ b_xyyþ b_xzz

b_y¼ b_yyyþ b_xxyþ b_yzz

b_z¼ b_zzzþ b_xxzþ b_yyz

1,1-Dimethylpiperazine-1,4-diium chloride iodide (4c)

The CH₃stretching modes are assigned at 2930 in the IR spec-

trum, 2910 cm^ꢁ1in the Raman spectrum and in the range 2954–

3054 cm^ꢁ1theoretically. The deformation and rocking modes of

the CH₃groups are observed at 1460, 1422, 1384, 1185, 1144,

1085 cm^ꢁ1in the IR spectrum and in the ranges 1383–1456 and

1071–1188 cm^ꢁ1theoretically. The CH₂stretching modes are

observed at 3002, 2980, 2959 cm^ꢁ1in the IR spectrum and 3004,

2961 cm^ꢁ1in the Raman spectrum and in the range 2951–

3022 cm^ꢁ1theoretically. The deformation modes of the CH₂groups

are assigned in the ranges, 1395–1455 (scissoring), 1294–1361

(wagging), 1144–1293 (twisting), 767–972 cm^ꢁ1(rocking) theo-

retically. These modes are observed at 1346, 1314, 1296, 1144,

971, 942, 839 cm^ꢁ1in the IR spectrum.

The ﬁrst order hyperpolarizability of the compounds 4a, 4b, 4c

are calculated and is found to be 6.284 ꢂ 10^ꢁ30, 7.510 ꢂ 10^ꢁ30, and

16.043 ꢂ 10^ꢁ30esu. The calculated hyperpolarizability of the title

compounds (1, 2, 3) are 48.34, 57.77 and 123.41 times that of

the standard NLO material urea (0.13 ꢂ 10^ꢁ30esu), respectively

[60]. The average second hyperpolarizability is h

c

i = (c_xxxx

+ c_yyyy+

c

_zzzz+ 2 _xxyy+ 2 _xxzz+ 2

c

c_yyzz)/5 [61–63]. The theoretical second

order hyperpolarizability was calculated using the Gaussian 09

software and is equal to ꢁ62.149 ꢂ 10^ꢁ40esu, ꢁ112.279 ꢂ 10^ꢁ40

esu, and ꢁ24.003 ꢂ 10^ꢁ40esu for compounds 4a, 4b, 4c. We con-

clude that the title compounds and its derivatives are an attractive

object for future studies of nonlinear optical properties.

The NH₂modes are assigned at 3295, 3254 (stretching), 1595,

1374, 841, 661 (deformations) theoretically and observed at

3441, 3322, 3236, 1589, 1371, 667 cm^ꢁ1in the Raman spectrum.

Here also there is a splitting for the NH₂stretching mode in the

IR spectrum which is due to the hydrogen bond with the neighbor-

ing units. The CN stretching modes are assigned at 906, 859 theo-

Molecular electrostatic potential

The molecular electrostatic potential is a useful method for

studying the interaction of a molecular system with its surround-

ings and is used for predicting sites and relative reactivity towards

electrophilic attack and in studies of biological recognition. The

MEP surface which is a method of mapping electrostatic potential

on to the isoelectron density surface and it provides a visual method

to understand the relative polarity [64]. To predict reactive sites of

electrophilic and nucleophilic attacks for the investigated molecule,

MEP at the B3LYP level optimized geometry was calculated. The dif-

ferent values of the electrostatic potential at the MEP surface are

represented by different colors; red,¹blue and green represent the

regions of most negative, most positive and zero electrostatic poten-

tial respectively. The MEP plots of the title compounds 4a, 4b, 4c are

shown in Figs. 13–15 and it provides a visual representation of the

chemically active sites and comparative reactivity of atoms. The

negative electrostatic potential corresponds to an attraction of proton

by the aggregate electron density in the molecule (shades of red and

yellow) and the positive electrostatic potential corresponds to the

repulsion of proton by the nuclei (shades of blue).

retically and a band is observed in the IR spectrum at 910 cm^ꢁ1

.

The piperazine ring stretching modes are observed at 1025, 1003,

942, 818, 790, 667 cm^ꢁ1in the IR spectrum and assigned in the

range 1012–661 cm^ꢁ1theoretically. Here also most of the modes

are not pure, but contains signiﬁcant contributions from other

modes. The FT-IR spectrum of 4c contains a lot of strong bands

in the region 2300–2800 cm^ꢁ1, which are overtones or combina-

tion bands and due to strong hydrogen bonding.

Nonlinear optical properties

Quantum chemical evaluation of the polarizability (

ﬁrst and second order hyperpolarizabilities (b and ) is a ﬁeld of

a), and the

c

intense research because it is related to the design of new com-

pounds for nonlinear optical applications and to understand the

interaction between electromagnetic ﬁeld and matter [57,58].

The hyperpolarizability and related properties have been calcu-

lated at DFT level by ﬁnite ﬁeld approach [59] which is currently

one of the methods for obtaining numerically accurate NLO

responses. The components of ﬁrst order hyperpolarizability are

deﬁned as the coefﬁcients in the Taylor series expansion of energy

in the external electric ﬁeld. The total static dipole moment, mean

polarizability and ﬁrst and second order hyperpolarizabilities can

be deduced using the x, y and z components as:

As can be seen from the Figs. 13–15, the negative electrostatic

potential regions are mainly localized over the chlorine and oxygen

atoms for compounds 4a and 4b and chlorine and iodine atoms of

compound 4c, and are possible sites for electrophilic attack. The

1

For interpretation of color in Figs. 13–15, the reader is referred to the web version

of this article.

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

223

Table 5

Calculated (scaled) wavenumbers, IR, Raman bands and assignments of 1-benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a).

B3LYP/6-311++G(d,p) (5D, 7F)

(cm^ꢁ1

IR_I

99

IR

Raman

Assignments^a

–

t

)

R_A

49

t

(cm^ꢁ1

)

t

(cm^ꢁ1

)

3303

3266

3083

3076

3067

3053

3047

3042

3033

3024

3022

3015

3012

3007

2972

2970

2961

2957

2954

2951

1594

1567

1556

1465

1456

1455

1447

1435

1433

1428

1427

1421

1403

1396

1390

1372

1366

1342

1327

1318

1309

1297

1292

1284

1241

1205

1184

1180

1164

1153

1152

1122

1117

1074

1013

1007

1006

997

3343

3181

–

3020

–

2994

–

2920

1590

–

1470

–

1452

–

3029

–

2977

–

2930

–

1463

–

1438

–

1289

–

1212

–

1165

–

1135

–

1060

–

t

NH₂(99)

NH₂(100)

CH(98)

CH(96)

CH(95)

CH₃(96)

CH₃(93)

CH(90)

107

1

0

1

4

5

7

3

1

5

3

4

19

1

2

93

270

69

72

22

50

40

49

14

52

60

32

160

84

256

33

8

5

6

91

5

2

7

1

0

2.75

1

6

12

2

6

2

0

2

0

3

1

7

1

4

11

10

3

49

3

4

23

3

1

3

1

4

20

0

6

5

34

1

0

7

0

4

2

CH(96)

CH₂(94)

CH₂(91)

CH2X(85)

CH₂(89)

CH₂(91)

CH₂(90)

CH₂(97)

CH₂(35),

CH₃(41),

CH₂(53),

CH₂(73),

t

CH₃(43),

t

CH₂X(16)

CH₂(10)

t

CH₂X(41),

CH₂X(32)

CH₂X(20)

t

4

83

20

3

dNH₂(98)

dCH(17),

dCH(11),

dCH(32),

t

Ph(72)

Ph(67)

Ph(59)

1

15

79

2

15

24

19

1

dCH₂(65), dCH₃(15)

dCH₃(38), dCH₂(50)

dCH₃(42), dCH₂(42)

dCH₃(35), dCH₂X(20), dCH₂(25)

dCH₂(64)

dCH₃(12), dCH(15), dCH₂(12), n

dCH₂(63), dCH₃(17)

dCH₂X(56), dCH₂(21)

dCH₃(55), dCH₂(19)

dCH₂(52), dCH₃(12)

dNH₂(37), dCH₂(41)

dNH₂(56), dCH₂(25)

dCH₂(66), dCH₃(15)

dCH₂(78)

tPh(44)

1425

–

1

11

17

36

2

1

6

33

10

5

1

12

7

1

36

7

3

7

0

4

–

1378

–

1321

1304

–

1210

–

dCH₂X(16), dCH₂(29)

dCH₂X(43), dCH₂(25)

dCH(53),

Ph(72)

dCH₂(72)

tPh(12)

t

dCH₂X(15), dCH₂(57), dNH₂(17)

dCH₂X(48), dCH₂(15), dNH₂(11)

dCH₂(11), dCH₂X(15)

tCC(37), tPz(46)

dCH₂(49), dNH₂(11)

dCH(69)

dCH₃(16), dCH₂(29), dPz(20)

tPh(15), dCH(74)

dCH₃(28), dCH₂(23), dNH₂(10)

dCH₃(35), dCH(44)

–

1163

–

5

6

4

8

3

0

1096

1078

1011

–

982

–

961

–

908

891

854

–

t

c

t

Ph(44), dCH(31)

Pz(70)

Ph(15),

Ph(42),

CH(81)

t

Pz(31)

Pz(11)

986

985

977

20

10

7

Pz(42), dCH₃(14), dCH₂(11)

dPz(21),

dPh(64), t

t

Pz(13), dCH₂(44)

Ph(23)

Pz(15)

971

7

dCH₂(58),

CH(92)

dCH₂X(22),

t

966

0

c

947

6

t

CN(16)

CH(77)

CN(16), tPz(12), dCH₂X(49)

916

1

–

888

–

842

–

c

t

886

5

848

845

826

12

18

0

dNH₂(16),

dNH₂(39),

t

Pz(24), dCH₂X(10)

CN(13), Pz(18), dCH₂(15)

3

0

6

5

16

3

t

c

t

CH(98)

797

1

CC(14), tPz(10), dPh(13), tPh(22)

Pz(37), dCH₂(43)

Pz(58), dCH₂(14)

777

1

773

753

23

25

s

Ph(22),

c

CH(46),

c

CC(11)

(continued on next page)

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

224

Table 5 (continued)

B3LYP/6-311++G(d,p) (5D, 7F)

IR

Raman

(cm^ꢁ1

)

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

15

2

32

5

0

19

3

2

1

2

0

5

0

1

10

1

t

(cm^ꢁ1

)

t

721

686

654

607

596

541

487

464

429

418

398

391

361

321

275

260

237

201

199

148

81

132

42

32

0

7

56

0

1

2

1

0

2

3

1

2

1

718

690

–

607

–

455

–

715

694

–

dNH₂(28),

t

Pz(31)

CH(27)

Ph(19), dPz(40)

s

Ph(55), c

dPh(86)

Ph(18), dPh(17), dCH₂X(16)

dPh(27), dCN(20), dPz(16)

s

dPz(41).

dPz(72)

sPh(10)

s

Ph(28), dCN(15), dPz(20), cCC(10)

Ph(39). dPz(32), sPz(19)

Ph(81)

dPz(51),

dCC(29),

s

Ph(10)

CH₂X(13), sCN(18), dPz(21)

s

Pz(60), dPz(30)

Pz(43), dCC(20),

CH₃(33), Pz(40), dCC(15)

Ph(13), dPz(22)

sCH₃(10)

s

CN(22),

CH₃(15),

CH₃(32),

–

79

–

s

Pz(62)

Pz(33)

–

1

CN(11),

CN(64),

s

Pz(61)

3

4

sPz(12), sCH₂X(10)

74

2

c

CC(37), CH₂X(34)

s

38

1

2

–

s

CH₂(52), sCN(30)

a

t

– stretching; d – in-plane deformation;

c

– out-of-plane deformation; s – torsion; Ph – phenyl ring; Pz – piperazine ring; X – C₁₅position; potential energy distribution

(%) is given in brackets in the assignment column. IR_I– IR intensity; R_A– Raman activity.

Table 6

Calculated (scaled) wavenumbers, IR, Raman bands and assignments of 1-Methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

B3LYP/6-311++G(d,p) (5D, 7F)

IR

Raman

(cm^ꢁ1

)

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

t

(cm^ꢁ1

)

t

3300

–

104

–

107

1

3

1

3

2

7

46

–

3454

3322

3185

–

3021

–

3012

2997

2980

–

2916

–

3316

–

3062

3054

3030

–

3011

2982

–

2957

–

2938

–

t

–

t

_asNH₂(99)

3258

3062

3050

3025

3022

3019

3009

3002

2972

2971

2966

2964

2960

2956

2952

2945

2944

2940

2936

2932

2928

2923

2918

2917

2912

2908

2903

2901

2900

2897

2896

2895

2894

2893

2892

97

26

42

18

49

51

54

4

222

51

113

24

90

32

133

3

13

15

2

9

1

19

1

35

38

2

_sNH₂(99)

_asCH₃(98)ring

_asCH₃(93)ring

_asCH₂Ring(95)

_asCH₂Ring(86)

_asCH₂Ring(95)

_asCH₂Ring(85)

_asCH₂(81)

_sCH₂Ring(77)

_sCH₂Ring(98)

_asCH₃(98)

4

5

42

11

22

72

1

_asCH₃Ring(26),

t

_sCH₂Ring(50)

_sCH₃Ring(53),

_asCH₃(88)

_sCH₂Ring(83)

_sCH₂Ring(95)

_asCH₂(71)

_asCH₂(67)

_asCH₂(61)

_asCH₂(57)

_asCH₂(63)

_asCH₂(62)

_asCH₂(58)

_asCH₂(64)

_asCH₂(65)

_asCH₂(67)

_asCH₂(65)

_asCH₂(58)

_sCH₃(98)

t_sCH₂Ring(25)

1

64

85

195

36

8

3

2

20

6

0

2

50

84

2

215

1

104

0

1

54

9

184

44

82

25

5

136

61

55

14

_asCH₂(74)

_asCH₂(61)

_asCH₂(57)

_sCH₂(65)

_sCH₂(88)

_sCH₂(65)

–

_sCH₂(74)

_sCH₂(60)

–

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

225

Table 6 (continued)

B3LYP/6-311++G(d,p) (5D, 7F)

IR

Raman

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

t

(cm^ꢁ1

)

t

(cm^ꢁ1

)

2892

2889

2887

2885

2883

2881

2880

2879

2877

2876

2875

1595

1461

1457

1456

1455

1454

1452

1450

1447

1444

1443

1440

1437

11436

1433

1431

1429

1428

1427

1426

1420

1406

1399

1392

1374

1370

1361

1352

1351

1348

1347

1346

1345

1340

1333

1329

1325

1320

1306

1295

1294

1293

1292

1290

1289

1288

1285

1284

1279

1278

1274

1273

1270

1263

1252

1249

0

1

3

1

0

854

35

19

1

56

1

2

7

3

5

8

1

21

2

9

10

3

1

2

3

1

0

280

77

13

260

45

434

173

171

25

24

2

14

5

2

0

8

0

1

0

8

3

13

0

10

27

150

7

1

10

7

0

1

5

1

2

1

0

2

4

1

0

1

3

2

1

0

5

7

3

2

1

4

3

2

73

1

–

2855

1597

1460

–

1442

–

1427

–

1400

–

1378

–

1360

–

2850

1606

–

1440

–

1410

–

1380

–

1358

–

t

_sCH₂(87)

_sCH₂(63)

_sCH₂(67)

_sCH₂(65)

_sCH₂(71)

_sCH₃(76)

_sCH₂(78)

_sCH₂(67)

_sCH₂(85)

_sCH₂(79)

_sCH₂(76)

dNH₂(98)

dCH₃Ring(21), dCH₂(38), dCH₂Ring(16)

dCH₂(76)

dCH₂(74)

dCH₃Ring(21), dCH₂Ring(69)

dCH₂(57)

dCH₃(40), dCH₂(14), dCH₂Ring(12)

dCH₃Ring(37), dCH₂(14), dCH₂Ring(12)

dCH₃(10), dCH₂(56)

dCH₃(14), dCH₂(54)

d_asCH₃(97)

dCH₃(13), dCH₂(55)

dCH₃(12), dCH₂(30), dCH₂Ring(35)

dCH₃(10), dCH₂(64)

dCH₃Ring(11), dCH₂(29), dCH₂Ring(23)

dCH₃Ring(41), dCH₂Ring(42)

dCH₂(84)

dCH₂(76)

dCH₂(68)

dCH₂(74)

dCH₃Ring(18), dCH₂Ring(50)

dCH₂(62), dCH₂Ring(10)

dCH₂(75)

dCH₂(90)

dCH₂(70)

0

3

dCH₂(35), dCH₂Ring(37)

dCH₃Ring(69)

11

4

13

39

1

2

0

1

2

0

1

0

6

11

3

2

1

3

2

3

2

1

2

1

0

dCH₂(13), dCH₂Ring(48)

dNH₂(33), dCH₂Ring(45)

dNH₂(59), dCH₂Ring(25)

dCH₂(10), dCH₂Ring(57), dCH₃(10)

d_sCH₃(85)

dCH₂(60)

dCH₂(69)

dCH₂(66)

dCH₂(48), dCH₂Ring(10)

dCH₂(27), dCH₂Ring(49)

dCH₂(69)

–

dCH₂(63)

–

dCH₂(55), dCH₂Ring(10)

dCH₃(37), dCH₂Ring(44)

dCH₂(41), dCH₂Ring(43)

dCH₂(88)

dCH₂(70)

dCH₂(62)

–

1318

–

1274

–

1317

–

1297

–

dCH₂(75)

dCH₂Ring(60)

dCH₂(58), dCH₂Ring(11)

dCH₂(50), dCH₂Ring(11)

dCH₂(64)

dCH₂(44), dCH₂Ring(10)

dCH₂(69)

dCH₂(75)

dCH₂(64)

dCH₂(70)

dCH₂(76)

dCH₂(40), dCH₂Ring(10)

dCH₂(86)

dCH₂(52)

dCH₂(67)

dCH₂(58)

–

1276

–

1250

3

0

–

(continued on next page)

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

226

Table 6 (continued)

B3LYP/6-311++G(d,p) (5D, 7F)

IR

Raman

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

t

(cm^ꢁ1

)

t

(cm^ꢁ1

)

1236

1232

1223

1213

1208

1193

1190

1181

1176

1172

1163

1159

1154

1123

1100

1098

1075

1048

1029

1027

1026

1024

1022

1019

1017

1010

1007

1003

996

989

982

979

978

973

969

958

951

946

939

935

920

900

869

863

847

841

831

800

798

775

771

767

748

731

719

711

707

705

704

673

581

505

501

486

469

464

444

430

417

398

376

355

1

0

1

0

1

0

2

1

2

1

10

2

1

0

1

0

1

0

3

1

6

4

6

3

1

7

10

3

5

10

2

7

4

0

4

9

7

2

1

35

1

2

6

7

0

1

17

0

1

0

2

1

6

3

2

1

6

3

1

2

0

1

0

1

0

4

1

2

5

3

7

–

1212

–

1170

–

1155

–

1094

–

1051

1032

–

1020

–

1000

–

951

–

1213

–

1196

–

1176

–

1161

–

1080

1050

1034

–

1023

–

1000

–

952

–

dCH₂(57)

dCH₂(66)

dNH₂(52)

dCH₂(46)

dCH₂(72)

dCH₂(60)

dCH₂(58)

dCH₂Ring(53), dNH₂(11)

dCH₂(66)

dCH₂(57)

sRing(36), dCH₃(34)

dCH₃(54)

dCH₂(65)

dCH₃(21), dCH₂Ring(24), dNH₂(11)

dCH₃(41), dCH₂(10)

dCH₃(53)

dCH₃(46),

dCH₃(10),

dCH₂(67)

58

60

5

0

2

t

CC(40)

CC(44)

t

CC(75)

CC(84)

CC(76)

CC(86)

Ring(27),

CC(71)

Ring(20),

Ring(40),

Ring(10),

Ring(49),

CC(77)

0

11

6

11

2

0

1

2

3

1

3

16

3

8

2

9

5

0

5

7

4

1

7

3

0

3

31

3

1

5

0

19

1

4

1

4

1

2

1

4

19

1

0

t

CC(34)

t

CC(37)

CC(18)

CC(39)

CC(22)

dRing(24), dCH₂Ring(43),

dCH₂Ring(17), Ring(48)

CC(42), dCH₂(14)

CC(54), dCH₂(20)

tRing(13)

t

dCH₂Ring(53)

t

Ring(46), dCH₃(10)

CC(80)

CC(44), dCH₂(20)

dCH₂(68)

–

t

CC(67)

CC(70)

CN(39),

CN(43),

935

917

893

–

933

916

890

–

844

–

828

805

–

719

–

706

–

t

CC(15)

CC(21)

dCH₂(35), dCH₃(13),

dCH₃(33), CC(43)

dNH₂(30), dCH₂Ring(41),

tRing(38), dCH₂(18)

dCH₂(38),

dCH₂(46),

tCC(15)

t

tRing(12)

–

830

801

775

–

721

–

t

Ring(20)

t

CN(30),

Ring(29), dCH₂Ring(34)

Ring(21)

Ring(45)

tRing(27)

dCH₂(48),

t

CN(17), t

dCH₂(67)

dCH₂(61)

dCH₂(58)

dCH₂(63)

dCH₂(71)

dCH₂(65)

dCH₂(70)

dNH₂(57)

–

705

–

670

590

511

–

483

–

460

444

–

420

392

375

–

673

591

515

–

490

–

463

441

–

421

–

tCN(34), tRing(35)

dRing(25), dCH₂(16), dCH₂Ring(15)

dRing(12), dCH₂(57)

dCH₂(57)

dRing(29), dCH₂(18)

dCH₂(48)

dRing(61), dCN(16)

dCH₂(49)

dCN(25), dCH₂(29)

dCN(46),

dCN(26), dCH₂(27)

dCH₂(44),

sRing(25)

–

360

s

Ring(19)

Ring(10)

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

227

Table 6 (continued)

B3LYP/6-311++G(d,p) (5D, 7F)

IR

Raman

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

t

(cm^ꢁ1

)

t

(cm^ꢁ1

)

331

318

303

283

273

244

235

204

199

185

170

166

156

152

142

136

133

114

113

100

93

90

86

67

63

61

44

39

34

27

22

15

11

1

2

0

1

0

2

0

1

0

4

2

4

0

1

0

1

0

1

4

5

0

1

0

7

0

3

1

0

1

0

–

297

–

272

–

232

208

–

118

–

104

–

dCN(23),

dCN(33),

dCN(13), dCH₂(43)

dRing(28), dCH₂(26)

s

Ring(33)

sRing(29), dRing(22)

sCH₃(33),

sRing(24)

dCN(15), dCH₂(43)

s

CH₃(91)

Ring(21), dCN(14), dCH₂(32)

CH₃(30), sRing(38)

CH₃(30), dCH₂(35)

CH₂(64)

CH₂(29),

CH₂(70)

CH₂(76)

CH₂(81)

s

Ring(23)

Ring(10)

dCH₂(37),

s

sCH₂(64)

sCH₂(75)

sCH₂(81)

sCH₂(73)

dCH₂(71)

s

CH₂(48)

CH₂(71)

CH₂(44)

CH₂(70)

83

–

CH₂(21), dCH₂(38)

CH₂(35),

CH₂(79)

CH₂(65)

sCH₃(15)

dCH₂(79)

sCH₂(78)

sCH₂(51)

sCH₂(65)

sCH₂(50)

–

a

t

– stretching; d – in-plane deformation;

c

– out of-plane deformation;

s

– torsion; as – asymmetric; s – symmetric; Ring-piperazine ring; potential energy distribution

(%) is given in the brackets of the assignment column; IR_I– IR intensity; R_A– Raman activity.

positive regions are localized on the piperazine ring for all com-

pounds indicating possible sites for nucleophilic attack. A region

of zero potential covers the benzene ring, leaving a more elec-

trophilic region in the plane of hydrogen atoms. A zero region of

potential covers the phenyl ring for 4a, CH₂chains for 4b and

hydrogen atoms for 4c leaving a more electrophilic region.

methyl group attached with the ring and the immediate CH₂groups

attached with the piperazine ring. While for the compound 4c,

HOMO is over the iodine, CH₃group attached with the nitrogen

and LUMO is localized over the entire molecule.

By using the HOMO and LUMO energy values, the global chemi-

cal reactivity descriptors such as hardness, chemical potential,

electronegativity and electrophilicity index as well as local reactiv-

ity have been deﬁned [69]. Pauling introduced the concept of elec-

tronegativity as the power of an atom in a molecule to attract

Frontier molecular orbitals

electrons to it. Hardness (

tronegativity are deﬁned using Koopman’s theorem as

= (I ꢁ A)/2, = ꢁ(I + A)/2 and = (I + A)/2, where I = ꢁE_HOMOand

g), chemical potential (l) and elec-

Both the highest occupied molecular orbital (HOMO) and lowest

unoccupied molecular orbital (LUMO) and their properties such as

energy are very useful for chemical reaction. The energy of HOMO

is directly related to the ionization potential and LUMO energy is

directly related to the electron afﬁnity [65,66] and this is also used

by the frontier electron density for predicting the most reactive posi-

(v)

g

l

v

A = ꢁE_LUMOare the ionization potential and electron afﬁnity of

the molecule. Considering the chemical hardness, large HOMO–

LUMO energy gap means a hard molecule and small gap means a

soft molecule. One can also relate the stability of the molecule to

hardness, which means that the molecule with least energy gap

means, it is more reactive. Parr et al. [69] have deﬁned a descriptor

to quantify the global electrophilic power of the molecule as elec-

tion in p-electron systems and also explains several types of reaction

in conjugated system [67]. The conjugated molecules are character-

ized by a small HOMO–LUMO separation, which is the result of a sig-

niﬁcant degree of intra-molecular charge transfer from the end-

capping electron-donor groups to the efﬁcient electron-acceptor

trophilicity index,

x = l g. The usefulness of this new reactivity

²/2

quantity has been recently demonstrated in understanding the

toxicity of various pollutants in terms of their reactivity and site

selectivity [70–76]. The global parameters of compounds, 4a, 4b,

4c are given in Table 8.

group through p-conjugated path [68]. The HOMO and LUMO plots

of the title compounds 4a, 4b and 4c are shown in Figs. 16–18. The

energy gap between the HOMO and LUMO orbital is a critical

parameter in determining molecular electrical transport properties

because it is a measure of electron conductivity. For compound 4a,

HOMO is localized over the chlorine atoms and piperazine ring,

while the LUMO is localized over the phenyl ring, N1 atom of the

piperazine ring the methylene group between the two rings. For

compound 4b, HOMO is over the piperazine ring and chlorine atoms

and the LUMO is over the piperazine ring, chlorine atoms, oxygen,

Natural bond orbital analysis

The natural bond orbital (NBO) calculations were performed

using NBO 3.1 program [77] as implemented in the Gaussian 09

package at the DFT/B3LYP level in order to understand various

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

228

Table 7

Calculated (scaled) wavenumbers, IR, Raman bands and assignments of 1,1-Dimethylpiperazine-1,4-diium chloride iodide (4c).

B3LYP/6-311++g(d,p) (5D, 7F)

IR

Raman

Assignments^a

–

t

(cm^ꢁ1

)

IR_I

R_A

t

(cm^ꢁ1

)

t

(cm^ꢁ1

)

3295

–

105

–

104

1

3

0

5

1

0

7

4

6

8

0

3

1

81

32

3

77

36

33

47

5

1

0

3

13

2

39

0

4

2

11

2

3

1

37

–

3441

3322

3236

–

3002

2980

–

2959

–

3004

–

2961

–

2910

–

t

–

t

_asNH₂(99)

3254

3054

3049

3045

3043

3022

3021

3009

3007

2970

2969

2959

2954

2951

2949

1595

1456

1455

1450

1442

1435

1426

1420

1418

1399

1395

1383

1374

1361

1344

1311

1294

1293

1249

1188

1182

1170

1144

1079

1071

1012

998

77

34

70

32

6

16

40

85

5

174

34

288

18

4

24

5

1

8

2

3

0

1

18

2

1

0

2

0

1

3

9

3

1

3

2

1

0

2

4

0

5

4

3

1

0

6

4

17

3

2

1

_sNH₂(99)

_asCH₃(96)

_asCH₃(99)

_asCH₃(98)

_asCH₃(99)

_asCH₂(85)

_asCH₂(91)

_asCH₂(87)

_asCH₂(92)

_sCH₂(95)

_sCH₂(97)

_sCH₂(46),

_sCH₂(41),

_sCH₂(99)

_sCH₃(97)

t

_sCH₃(40)

_sCH₃(54)

–

2930

1589

1460

–

1422

–

dNH₂(98)

d_asCH₃(82)

dCH₂(59), d_asCH₃(23)

dCH₂(52), d_asCH₃(33)

dCH₂(30), d_asCH₃(60)

dCH₂(72), d_asCH₃(14)

d_asCH₃(62)

dCH₂(68), d_asCH₃(24)

dCH₂(36), d_asCH₃(48)

dCH₂(36), d_asCH₃(43)

dCH₂(25), d_asCH₃(48)

dNH₂(37), dCH₂(44)

dCH₂(22), d_asCH₃(54)

dNH₂(58), dCH₂(26)

dCH₂(76)

dCH₂(85)

dCH₂(56)

dCH₂(71)

dNH₂(22), dCH₂(58)

dNH₂(37), dCH₂(18), dCH₃(14),

dCH₃(60)

dCH₂(54), dNH₂(12)

dCH₃(25), dCH₂(34), tCN(23)

dCH₃(35), dCH₂(37), dNH₂(14)

dCH₃(72)

dCH₃(44), dCH₂(14)

t

–

1384

1371

–

1346

1314

–

1296

1251

1185

–

tCN(19)

–

1

0

7

11

7

1144

1085

–

1025

1003

–

971

942

910

–

839

818

790

–

Ring(80)

Ring(46), dCH₂(20), dRing(11)

Ring(42), dCH₂(20), dRing(12)

Ring(12), dCH₂(64)

989

972

954

906

859

841

829

771

767

661

550

461

448

424

6

12

15

21

34

9

4

0

1

6

0

1

Ring(42), dCH₂(40)

CN(45),

CN(43),

t

Ring(24)

Ring(23)

dNH₂(44), dCH₂(38)

t

Ring(70)

Ring(63)

Ring(26), dCH₂(54)

Ring(44), dNH₂(38)

667

–

454

438

–

dRing(42), dCH₂(18)

dRing(66), dCN(10)

dRing(41), dCN(40)

–

sRing(22), dCN(47)

413

343

311

305

0

3

0

1

0

400

–

dCN(72)

sRing(39), dCN(27), dRing(17)

sRing(42), dCN(25), dRing(24)

sRing(15), dCN(47), dRing(10), sCH₃(17)

–

260

0

–

dCN(27),

sCH₃(65)

233

177

150

0

2

0

–

228

–

147

s

Ring(49), dCN(11), sCH₃(35)

Ring(29),

Ring(89)

sCH₃(68)

a

t

– stretching; d – in-plane-deformation;

c – out-of-plane deformation; s – torsion; as – asymmetric; s – symmetric; potential energy distribution (%) is given in brackets

in the assignment column; IR_I– IR intensity; R_A– Raman activity.

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

229

Fig. 15. MEP plot of 1,1-dimethylpiperazine-1,4-diium chloride iodide (4c).

Fig. 13. MEP plot of 1-benzyl-1-methylpiperazine-1,4-diium dichloride monohy-

drate (4a).

In NBO analysis large E(2) value shows the intensive interaction

between electron-donors and electron-acceptors, and greater the

extent of conjugation of the whole system, the possible intensive

interaction for compounds 4a, 4b, 4c are given in Tables 9–11.

second-order interactions between the ﬁlled orbital of one subsys-

tem and vacant orbital of another subsystem, which is a measure of

the intermolecular delocalization or hyper conjugation. NBO analy-

sis provides the most accurate possible ‘natural Lewis structure’

picture of ‘j’ because all orbital details are mathematically chosen

to include the highest possible percentage of the electron density.

A useful aspect of the NBO method is that it gives information

about interactions of both ﬁlled and virtual orbital spaces that

could enhance the analysis of intra and inter molecular interac-

tions. The second-order Fock-matrix was carried out to evaluate

the donor–acceptor interactions in the NBO basis. The interactions

result in a loss of occupancy from the localized NBO of the idea-

lized Lewis structure into an empty non-Lewis orbital. For each

donor (i) and acceptor (j) the stabilization energy (E2) associated

with the delocalization i ? j is determined as

Compound 4a

The second-order perturbation theory analysis of Fock-matrix

in NBO basis shows strong intermolecular hyper conjugative inter-

actions are formed by orbital overlap between n(Cl), n(O) and

r^⁄(NAH), r^⁄(CAN) bond orbital which result in intra-molecular

charge transfer (ICT) causing stabilization of the system. There

occurs an inter-molecular hyper-conjugative interaction N₂AH₃₃

from Cl₃₆of n₃(Cl₃₆) ? r^⁄(N₂AH₃₃

)

which increases ED

(0.01437e) that weakens the respective bonds N₂AH₃₃leading to

stabilization of 0.57 kJ/mol. Another hyper-conjugative interaction

of N₂AC₉from O₃₇of n₃(O₃₇) ? r^⁄(N₂AC₉) which increases ED

(0.02250e) that weakens the respective bonds N₂AC₉leading to

stabilization of 0.82 kJ/mol. These interactions are observed as an

increase in electron density (ED) in CN, NH orbital that weakens

the respective bonds. The hyper-conjugative interaction energy

was deduced from the second-order perturbation approach.

Delocalization of electron density between occupied Lewis-type

(bond or lone pair) NBO orbital and formally unoccupied (anti-

2

ðF_i;jÞ

Eð2Þ ¼ E_ij¼ q_i

D

ðE_jꢁ E_iÞ

q_i? donor orbital occupancy,

E_i, E_j? diagonal elements,

F_ij? the off diagonal NBO Fock matrix element.

bond or Rydberg) non-Lewis NBO orbital corresponds to a

Fig. 14. MEP plot of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

Table 8

Chemical parameters of 4a, 4b and 4c.

Compound

HOMO

LUMO

I

A

E_gap

g

l

v

x

4a

4b

4c

ꢁ8.342

ꢁ8.243

ꢁ5.869

ꢁ4.711

ꢁ1.741

ꢁ1.607

8.342

8.243

5.869

4.711

1.741

1.607

3.631

6.502

4.262

1.816

3.251

0.804

ꢁ6.527

ꢁ4.992

ꢁ3.738

6.527

4.992

3.738

11.730

3.833

8.689

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

230

Fig. 16. HOMO and LUMO plots of 1-benzyl-1-methylpiperazine-1,4-diium dichlo-

ride monohydrate (4a).

Fig. 18. HOMO and LUMO plots of 1,1-dimethylpiperazine-1,4-diium chloride

iodide (4c).

stabilizing donor–acceptor interaction. The NBO analysis also

describes the bonding in terms of the natural hybrid orbital

n₂(Cl₃₅), which occupy a higher energy orbital (ꢁ0.220733 a.u.)

with considerable p-character (100.0%) and low occupation num-

ber (1.97878) and the other n₁(Cl₃₅) occupy a lower energy orbital

(ꢁ0.66361 a.u.) with p-character (12.21%) and high occupation

number (1.99901). The NBO analysis also describes the bonding

in terms of the natural hybrid orbital n₂(Cl₃₆), which occupy a

higher energy orbital (ꢁ0.26321 a.u.) with considerable p-charac-

ter (99.73%) and low occupation number (1.99211) and the other

n₁(Cl₃₆) occupy a lower energy orbital (ꢁ0.80033 a.u.) with p-char-

acter (17.56%) and high occupation number (1.99843). The NBO

analysis also describes the bonding in terms of the natural hybrid

occupation number (1.99048) and the other n₁(O₃₇) occupy a lower

energy orbital (ꢁ0.34315 a.u.) with p-character (93.71%) and high

occupation number (1.99537). Thus, a very close to pure p-type

lone pair orbital participates in the electron donation to the

n₃(Cl₃₆) ? r^⁄(N₂AH₃₃), n₃(O₃₇) ? r^⁄(N₂AC₉) interactions in the

compound. The results are tabulated in Table 12.

Compound 4b

The second-order perturbation theory analysis of Fock-matrix

in NBO basis shows strong intermolecular hyper conjugative inter-

actions are formed by orbital overlap between n(O),n(Cl) and

r^⁄(NAC), r^⁄(CAC) bond orbitals which result in ICT causing

orbital n₂(O₃₇), which occupy

a

higher energy orbital

(ꢁ0.585551 a.u.) with considerable p-character (57.17%) and low

Fig. 17. HOMO and LUMO plots of 1-methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

231

Table 9

Second-order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra molecular bonds of 1-Benzyl-1-methylpiperazine-1,4-diium dichloride

monohydrate (4a).

c

Donor(i)

Type

ED/e

Acceptor(j)

Type

ED/e

E(2)^a

E(j) ꢁ E(i)^b

F(i,j)

N1AC3

–

r

–

1.98436

–

N1AC12

N1AC15

N1AC29

r^⁄

0.03522

0.05467

0.02430

0.77

0.67

0.60

0.96

0.95

0.98

0.025

0.023

0.022

N1AC12

r

–

1.98036

N1AC3

r^⁄

0.03630

0.05467

0.02430

0.02154

0.76

0.87

0.63

1.32

0.95

0.92

0.95

1.13

0.024

0.025

0.022

0.035

–

N1AC15

N1AC29

C15AC18

N1AC15

r

–

1.97609

N1AC3

N1AC12

N1AC29

C3AC6

r^⁄

0.03630

0.03522

0.02430

0.01271

0.01155

0.79

0.77

0.75

1.59

1.46

0.93

0.92

0.94

1.03

1.06

0.024

0.036

0.035

–

C9AC12

N1AC29

–

r

–

1.98467

–

N1AC3

N1AC12

N1AC15

r^⁄

0.03630

0.03522

0.05467

0.68

0.76

0.96

0.95

0.93

0.023

0.024

N2AH33

–

r

–

1.98273

–

C3AC6

C9AC12

r^⁄

0.01271

0.01155

2.02

1.82

1.02

1.05

0.041

0.039

r^⁄

C3AC6

–

r

–

1.98387

–

N1AC15

N2AH33

r^⁄

0.05467

0.01437

2.29

1.80

0.88

1.01

0.040

0.038

C9AC12

–

r

–

1.98458

–

N1AC15

N2AH33

r^⁄

0.05467

0.01437

1.83

1.79

0.86

0.99

0.036

0.038

r^⁄

C15AC18

r

–

1.97882

N1AC12

C18AC19

C18AC27

C19AC21

C25AC27

r^⁄

0.03522

0.02578

0.02479

0.32509

0.01498

1.51

2.03

1.92

2.27

2.23

0.87

1.22

1.23

1.24

0.033

0.044

0.043

0.047

–

C18AC19

–

r

–

1.97410

–

C15AC18

C18AC27

r^⁄

0.02154

0.02479

1.89

3.63

1.11

1.27

0.041

0.061

r^⁄

C19AC21

–

r

–

1.97795

–

C15AC18

C18AC19

C21AC23

r^⁄

0.02154

0.02578

0.01609

4.01

3.49

2.68

1.11

1.27

1.28

0.060

0.059

0.052

C21AC23

–

r

–

1.97968

–

C19AC21

C23AC25

r^⁄

0.01544

0.01609

2.77

2.56

1.28

0.053

0.051

r^⁄

C23AC25

–

r

–

1.98012

–

C21AC23

C25AC27

r^⁄

0.01609

0.30196

2.58

2.67

1.27

1.28

0.051

0.052

C25AC27

–

r

–

1.97822

–

C15AC18

C18AC27

C23AC25

r^⁄

0.02154

0.02479

0.01609

3.94

3.23

2.65

1.11

1.26

1.28

0.059

0.057

0.052

LPCl36

–

n

–

p

1.98668

1.71326

–

N2AH33

N2AC6

N2AC9

r^⁄

0.01437

0.02000

0.02250

0.06

0.25

0.57

0.56

0.57

0.82

0.005

0.006

0.013

LPO37

1.99048

a

b

c

E(2) means energy of hyper-conjugative interactions (stabilization energy in kJ/mol).

Energy difference between donor and acceptor i and j NBO orbitals in a.u.

F(i,j) is the Fock matrix elements between i and j NBO orbitals in a.u.

Table 10

Second-order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra molecular bonds of 1-Methyl-1-octadecylpiperazine-1,4-diium dichloride

monohydrate (4b).

Donor(i)

Type

ED/e

Acceptor(j)

Type

ED/e

E(2)^a

E(j) ꢁ E(i)^b

F(i,j)^c

N2AC6

N2AC9

C3AC6

C9AC12

LP O76

LP Cl79

–

LP Cl80

–

r

–

p

n

d

1.98874

1.98740

1.98618

1.98641

1.99430

1.90892

–

1.99506

1.97052

1.82691

–

N2AC9

N2AC6

N1AC19

C9AC12

N2AC6

N2AC9

C9AC12

C3AC6

N2AC6

N2AC9

C3AC6

C9AC12

r^⁄

0.02024

0.01991

0.03667

0.01445

0.01991

0.02024

0.01445

0.01381

0.01991

0.02024

0.01381

0.01445

0.51

2.16

1.96

0.39

0.06

0.14

0.19

0.16

0.19

0.08

1.02

1.01

0.87

0.73

0.56

0.57

0.56

0.57

0.64

0.63

0.64

0.020

0.039

0.037

0.015

0.005

0.008

0.009

0.010

0.007

–

d

–

a

b

c

E(2) means energy of hyper-conjugative interactions (stabilization energy in kJ/mol).

Energy difference between donor and acceptor i and j NBO orbitals in a.u.

F(i,j) is the Fock matrix elements between i and j NBO orbitals in a.u.

ˇ ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

232

Table 11

Second-order perturbation theory analysis of Fock matrix in NBO basis corresponding to the intra molecular bonds of 1,1-Dimethylpiperazine-1,4-diium chloride iodide (4c).

Donor(i)

Type

ED/e

Acceptor(j)

Type

ED/e

E(2)^a

E(i) ꢁ E(j)^b

F(i,j)^c

C5AC8

C11AC14

Cl2AH25

–

LP I1

LP Cl2

LP N 4

–

r

–

r

n

r

–

1.98628

1.98645

1.99608

–

1.99964

1.99996

1.83532

–

N3AC17

N4AC8

N4AC11

N4AH26

C5AC8

C11AC14

C5AC8

C11AC14

Cl2AH25

C5AC8

r^⁄

0.02261

0.02716

0.02170

0.01967

0.01981

0.02451

0.02716

0.02451

0.02716

0.11209

0.02451

0.02716

3.02

3.15

0.37

0.27

0.06

0.18

0.24

0.14

39.48

6.88

7.44

0.85

0.87

0.90

1.04

0.96

0.93

0.50

0.58

0.51

0.67

0.64

0.045

0.047

0.016

0.014

0.007

0.012

0.010

0.008

0.128

0.063

0.064

–

C11AC14

a

b

c

E(2) means energy of hyper-conjugative interactions (stabilization energy in kJ/mol).

Energy difference between donor and acceptor i and j NBO orbitals in a.u.

F(i,j) is the Fock matrix elements between i and j NBO orbitals in a.u.

Table 12

NBO results showing the formation of Lewis and non-Lewis orbitals of 1-Benzyl-1-methylpiperazine-1,4-diium dichloride monohydrate (4a).

Bond (AAB)

ED/e^a

EDA%

EDB%

NBO

s%

p%

r

–

r

–

r

–

r

–

r

–

r

–

r

–

r

–

r

–

r

–

r

–

r

–

N1AC3

1.98436

65.29

–

66.89

–

67.62

–

67.23

–

63.24

–

64.44

–

49.78

–

50.32

–

50.30

–

50.82

–

51.15

–

50.45

–

50.08

–

50.17

–

50.01

–

49.74

–

50.91

–

34.71

–

33.11

–

32.38

–

32.77

–

36.76

–

35.56

–

50.22

–

49.68

–

49.70

–

49.18

–

48.85

–

49.55

–

49.92

–

49.83

–

49.99

–

50.26

–

49.09

–

0.8080(sp^3.00)N

+0.5891(sp^3.74)C

0.8178(sp^3.04)N

+0.5754(sp^4.13)C

0.8223(sp^3.06)N

+0.5691(sp^4.33)C

0.8200(sp^2.90)N

+0.5724(sp^3.90)C

0.7952(sp^2.41)N

+0.6063(sp^3.61)C

0.8027(sp^2.32)N

+0.5963(sp^3.81)C

0.7055(sp^2.50)C

+0.7087(sp^2.40)C

0.7094(sp^2.41)C

+0.7048(sp^2.48)C

0.7092(sp^2.15)C

+0.7050(sp^2.26)C

0.7129(sp^1.89)C

+0.7013(sp^1.78)C

0.7152(sp^1.89)C

+0.6990(sp^1.83)C

0.7103(sp^1.79)C

+0.7039(sp^1.80)C

0.7077(sp^1.00)C

+0.7065(sp^1.00)C

0.7083(sp^1.80)C

+0.7059(sp^1.81)C

0.7072(sp^1.80)C

+0.7071(sp^1.81)C

0.7052(sp^1.80)C

+0.7090(sp^1.81)C

0.7135(sp^1.00)C

0.7006(sp^1.00)C

sp^4.79

25.0

75.00

78.92

75.23

80.52

75.41

81.28

74.36

ꢁ0.77319

1.98036

ꢁ0.74836

1.97609

ꢁ0.72896

1.98467

ꢁ0.75829

1.98948

ꢁ0.798459

1.98959

ꢁ0.78698

1.98387

ꢁ0.70363

1.98458

ꢁ0.68808

1.97882

ꢁ0.68142

1.97410

ꢁ0.72594

1.97280

ꢁꢁ0.71948

1.97795

ꢁ0.72601

1.66328

ꢁ0.28015

1.97968

ꢁ0.72342

1.98012

ꢁ0.72193

1.97822

ꢁ0.72090

1.64051

ꢁ0.27334

1.66029

ꢁ0.42986

1.99901

ꢁ0.66361

1.97878

ꢁ0.22073

1.95733

ꢁ0.23413

1.92617

ꢁ0.27516

1.99843

ꢁ0.80033

1.99211

ꢁ0.26321

1.98668

ꢁ0.26913

1.71326

ꢁ

21.08

24.77

19.48

24.59

18.72

25.64

20.3579.65

29.33

21.66

30.07

20.75

28.57

29.38

29.28

28.72

31.75

30.62

34.65

35.95

34.64

35.3

35.87

35.69

0.01

N1AC12

N1AC15

N1AC29

N2AC6

70.67

78.34

69.93

79.25

71.43

70.62

70.72

71.28

68.25

69.38

65.35

64.22

65.36

64.70

64.13

64.31

99.99

100.0

64.27

64.37

64.28

64.39

64.25

64.43

100.0

99.99

82.73

–

12.21

–

100.0

–

2.10

–

89.85

–

17.56

–

99.73

–

99.04

–

N2AC9

C3AC6

C9AC12

C15AC18

C18AC19

C18AC27

C19AC21

pC19AC21

–

r

–

r

–

r

–

0.00

C21AC23

C23AC25

C25AC27

35.73

35.63

35.72

35.61

35.75

35.57

0.00

0.01

17.27

–

pC25AC27

–

n1 N2

–

n1 Cl35

–

n2 Cl35

–

n3 Cl35

–

n4 Cl35

–

n1 Cl36

–

n2 Cl36

–

n3 Cl36

–

n4 Cl36

–0.33593

–

sp^0.14

87.79

–

0.00

–

sp^1.00

–

sp^47.07

97.90

–

10.15

–

82.44

–

0.27

–

0.96

–

16.32

–

sp^8.85

–

sp^0.21

–

sp^99.99

–

sp^99.99

–

sp^5.12

83.68

–

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

233

Table 12 (continued)

Bond (AAB)

ED/e^a

1.99537

EDA%

EDB%

NBO

s%

p%

n1 O37

–

n2 O37

–

sp^14.90

29.0

–

42.83

–

93.71

–

57.17

–

ꢁ0.34315

–

1.99048

sp^1.33

–

ꢁ0.58555

–

a

ED/e in a.u.

Table 13

NBO results showing the formation of Lewis and non-Lewis orbitals of 1-Methyl-1-octadecylpiperazine-1,4-diium dichloride monohydrate (4b).

Bond (AAB)

ED/e^a

EDA%

EDB%

NBO

s%

p%

r

–

r

–

r

–

r

–

N2AC6

N2AC9

C3AC6

C9AC12

1.98874

ꢁ0.76520

1.98740

62.42

–

63.06

–

51.03

–

48.65

–

37.58

–

36.94

–

48.97

–

51.35

–

0.7901(sp^2.88)N

25.76

22.86

26.01

21.90

29.46

29.16

29.13

30.01

35.01

–

12.50

–

0.32

–

1.28

–

15.28

–

74.24

77.14

73.99

78.10

70.54

70.85

70.87

69.99

64.90

–

87.50

–

99.68

–

98.72

–

84.73

–

+0.6130(sp^3.37)C

0.7941(sp^2.84)N

ꢁ0.75629

+0.6078(sp^3.56)C

1.98618

0.7144(sp^2.39)C

ꢁ0.69526

1.98641

+0.6998(sp^2.43)C

0.6975(sp^2.43)C

ꢁ0.69427

+0.7166(sp^2.33)C

n1 O76

–

n4 Cl79

–

n2 Cl80

–

n3 Cl80

–

1.99430

sp^1.85

–

ꢁ0.50777

1.90892

sp^7.00

–

ꢁ0.30301

1.99506

sp^99.99

–

ꢁ0.23305

1.97052

sp^77.25

–

ꢁ0.24093

n4 Cl80

–

1.82691

sp^5.54

–

ꢁ0.31155

a

ED/e in a.u.

Table 14

NBO results showing the formation of Lewis and non-Lewis orbitals of 1,1-Dimethylpiperazine-1,4-diium chloride iodide (4c).

Bond (AAB)

ED/e^a

EDA%

EDB%

NBO

s%

p%

r

–

r

–

r

–

n1 I1

C5AC8

1.98628

50.85

–

48.44

–

49.15

–

51.56

–

0.7131(sp^2.43)C

+0.7011(sp^2.46)C

0.6960(sp^2.53)C

+0.7181(sp^2.41)C

0.8240(sp^4.77)Cl

29.19

28.90

28.30

29.31

17.33

100.00

95.06

–

0.17

–

16.56

–

70.81

71.10

71.70

70.69

82.67

0.00

4.94

–

99.83

–

83.44

–

ꢁ0.68709

1.98645

ꢁ0.57563

0.11209

0.14464

1.99964

ꢁ0.53656

1.99521

ꢁ0.30588

1.83532

ꢁ0.36617

C11AC14

Cl2AH25

67.90

32.10

–

+0.5666(sp^0.00

)

sp^0.05

–

n3 Cl2

–

n1 N4

–

sp^99.99

–

sp^5.04

–

a

ED/e in a.u.

stabilization of the system. These interactions are observed as an

increase in electron density (ED) in NAC and CAC orbital that

weakens the respective bonds. There occurs a strong inter molecu-

lar hyper conjugative interaction of C₉AC₁₂from O₇₆of

n₁(O₇₆) ? r^⁄(C₉AC₁₂) which increases ED (0.01445e) that weakens

the respective bonds C₉AC₁₂leading to stabilization of 0.39 kJ/mol.

There occurs an inter-molecular hyper-conjugative interaction of

N₂AC₆from Cl₇₉of n₄(Cl₇₉) ? r^⁄(N₂AC₆) which increases ED

(0.01991e) that weakens the respective bonds N₂AC₆leading to

stabilization of 0.06 kJ/mol and also the hyper-conjugative interac-

tion of C₉AC₁₂from O₂₁of n₂(Cl₈₀) ? r^⁄(C₉AC₁₂) which increases

ED (0.01445e) that weakens the respective bonds C₉AC₁₂leading

to stabilization of 0.14 kJ/mol. Again a hyper-conjugative interac-

tion of N₂AC₉from Cl₈₀of n₂(Cl₈₀) ? r^⁄(N₂AC₉) which increases

ED (0.02024e) that weakens the respective bonds N₂AC₉leading

to stabilization of 0.19 kJ/mol. These interactions are observed as

an increase in electron density (ED) in CAC and CAO orbitals that

weakens the respective bonds.

The NBO analysis also describes the bonding in terms of the

natural hybrid orbital n₃(Cl₈₀), which occupy a higher energy orbi-

tal (ꢁ0.24093 a.u.) with considerable p-character (98.72%) and low

occupation number (1.97052) and the other n₂(Cl₈₀) occupy a

lower energy orbital (ꢁ0.23305 a.u.) with p-character (99.68%)

and high occupation number (1.99506). Thus, a very close to pure

p-type lone pair orbital participates in the electron donation to the

n₁(O₇₆) ? r^⁄(C₉AO₁₂), n₄(Cl₇₉) ? r^⁄(N₂AC₆), n₂(Cl₈₀) ? r^⁄(C₉AC₁₂),

n₂(Cl₈₀) ? r^⁄(N₂AC₉) interaction in the compound. The results

are tabulated in Table 13.

ˇ

234

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

Table 15

Table 16

The charge distribution calculated by the Mulliken and natural bond orbital (NBO)

methods of compound 4a.

methods of compound 4b.

Atoms

Natural charge

Atomic charges (Mulliken)

Atoms

Natural charge

Atomic charges (Mulliken)

1 Cl

2 Cl

3 O

4 H

5 H

6 N

7 N

8 C

ꢁ0.82300

ꢁ0.72892

ꢁ1.01984

0.47765

0.49436

ꢁ0.29955

ꢁ0.65802

ꢁ0.28967

0.26926

0.29099

ꢁ0.28059

0.28059

0.24997

ꢁ0.29891

0.28821

0.28046

ꢁ0.29773

0.31014

0.27564

ꢁ0.26673

0.26160

0.30011

ꢁ0.10393

ꢁ0.22691

0.24028

ꢁ0.22868

0.24391

ꢁ0.21718

0.24314

ꢁ0.22443

0.24710

ꢁ0.20844

0.26588

ꢁ0.49063

0.25085

0.28996

0.23964

0.45190

0.41154

ꢁ0.724708

ꢁ0.636036

ꢁ0.839498

0.388750

0.413893

ꢁ0.385339

ꢁ0.606925

ꢁ0.168862

0.199696

0.243499

ꢁ0.179377

0.217729

0.197044

ꢁ0.214870

0.255317

0.214625

ꢁ0.181984

0.259786

0.225901

ꢁ0.270293

0.204389

0.256594

0.123098

ꢁ0.185491

0.146263

ꢁ0.132479

0.144748

ꢁ0.121668

0.144768

ꢁ0.132232

0.151163

ꢁ0.181490

0.195258

ꢁ0.363219

0.205280

0.254822

0.180144

0.382004

0.319698

1 N

2 N

3 C

4 H

5 H

6 C

7 H

8 H

ꢁ0.31942

ꢁ0.65124

ꢁ0.21008

0.21279

0.27521

ꢁ0.19478

0.24252

0.21719

ꢁ0.22001

0.21090

0.28764

ꢁ0.20076

0.27179

0.21259

ꢁ0.35327

0.22039

0.21212

0.21430

ꢁ0.15733

0.20240

0.24386

ꢁ0.39910

0.20360

0.19255

ꢁ0.36253

0.19937

0.18820

ꢁ0.36538

0.18387

0.18791

ꢁ0.36563

0.18462

0.18812

ꢁ0.36502

0.18286

0.18457

ꢁ0.36496

0.18470

0.18330

ꢁ0.36476

0.18332

0.18250

ꢁ0.36476

0.18344

0.18278

ꢁ0.36465

0.18280

0.18236

ꢁ0.36466

0.18291

0.18255

ꢁ0.36459

0.18256

0.18231

ꢁ0.36461

0.18263

0.18241

ꢁ0.36459

0.18246

0.18229

ꢁ0.36572

0.18204

0.18191

ꢁ0.36946

0.18147

0.18160

ꢁ0.36273

0.18267

0.18279

ꢁ0.56172

0.19413

0.18709

0.18697

ꢁ0.371920

ꢁ0.299981

ꢁ0.144628

0.157181

0.213420

ꢁ0.085066

0.180511

0.167564

ꢁ0.113458

0.157695

0.202655

ꢁ0.143271

0.213928

0.155453

ꢁ0.177303

0.168117

0.151984

0.156659

ꢁ0.118559

0.147610

0.209721

ꢁ0.223321

0.138125

0.120181

ꢁ0.218802

0.133546

0.112447

ꢁ0.206943

0.104648

0.112089

ꢁ0.204902

0.104892

0.111713

ꢁ0.203907

0.101980

0.105322

ꢁ0.201928

0.105197

0.102259

ꢁ0.202499

0.102731

0.101016

ꢁ0.201039

0.102755

0.101274

ꢁ0.201888

0.101645

0.100661

ꢁ0.200777

0.101699

0.100854

ꢁ0.201587

0.101147

0.100533

ꢁ0.200863

0.101194

0.100670

ꢁ0.201277

0.100908

0.100502

ꢁ0.199907

0.100552

0.100198

ꢁ0.202680

0.099914

0.100193

ꢁ0.221957

0.103068

0.103349

ꢁ0.289218

0.105901

0.101349

0.101102

9 H

9 C

10 H

11 H

12 H

13 H

14 C

15 H

16 H

17 C

18 H

19 H

20 C

21 H

22 H

23 C

24 C

25 H

26 C

27 H

28 C

29 H

30 C

31 H

32 C

33 H

34 C

35 H

36 H

37 H

38 H

39 H

10 H

11 H

12 C

13 H

14 H

15 C

16 H

17 H

18 H

19 C

20 H

21 H

22 C

23 H

24 H

25 C

26 H

27 H

28 C

29 H

30 H

31 C

32 H

33 H

34 C

35H

36 H

37 C

38 H

39 H

40 C

41 H

42 H

43 C

44 H

45 H

46 C

47 H

48 H

49 C

50 H

51 H

52 C

53 H

54 H

55 C

56 H

57 H

58 C

59 H

60 H

61 C

62 H

63 H

64 C

65 H

66 H

67 C

68 H

69 H

70 C

71 H

72 H

73 H

Compound 4c

The second-order perturbation theory analysis of Fock-matrix

in NBO basis shows strong intermolecular hyper conjugative inter-

actions are formed by orbital overlap between n(N), n(Cl), n(I) and

r^⁄(ClAH), r^⁄(CAC) bond orbitals which result in ICT causing

stabilization of the system. These interactions are observed as an

increase in electron density (ED) in ClAH and CAC orbital that

weakens the respective bonds. There occurs a strong inter molecu-

lar hyper conjugative interaction of C₅AC₈from I₁of

n₁(I₁) ? r^⁄(C₅AC₈) which increases ED (0.02451e) that weakens

the respective bonds C₅AC₈leading to stabilization of 0.24 kJ/mol

and also the hyper-conjugative interaction of C₁₁AC₁₄from Cl₂of

n₃(Cl₂) ? r^⁄(C₁₁AC₁₄) which increases ED (0.02716e) that weak-

ens the respective bonds C11AC14 leading to stabilization of

0.14 kJ/mol. Again a hyper-conjugative interaction of Cl₂AH₂₅from

N₄of n₁(N₄) ? r^⁄(Cl₂AH₂₅) which increases ED (0.112090e) that

weakens the respective bonds Cl₂AH₂₅leading to stabilization of

39.48 kJ/mol. The increased electron density at the oxygen atoms

leads to the elongation of respective bond length and a lowering

of the corresponding stretching wave number. The electron density

(ED) is transferred from the n(Cl) to the r^⁄orbital of the CAH bond,

explaining both the elongation and the red shift [78]. The hyper

conjugative interaction energy was deduced from the second-order

perturbation approach. Thus, a very close to pure p-type lone pair

orbital participates in the electron donation to the

n₁(I₁) ? r^⁄(C₅AC₈), n₃(Cl₂) ? r^⁄(C₁₁AC₁₄), n₁(N₄) ? r^⁄(Cl₂AH₂₅

interaction in the compound. The results are tabulated in Table 14.

)

ˇ

D. Nemecková et al. / Journal of Molecular Structure 1094 (2015) 210–236

235

1.5062 (XRD) for compound 4b and 1.4678–1.5241 (DFT),

1.4590–1.5134 (XRD) for compound 4c. The CC bond lengths of

the piperazine rings are 1.5176, 1.5250 (DFT), 1.5100, 1.5400

(XRD) for compound 4a, 1.5243m 1.5248 (DFT), 1.5042, 1.5013

(XRD) for compound 4b and 1.5229, 1.5300 (DFT), 1.5310, 1.5270

(XRD) for compound 4c. The discrepancies between the calculated

values and the experimental results are due to the fact that com-

parison made between the experimental data, obtained from single

crystal and calculated results and for isolated molecule in the gas-

eous phase.

Table 16 (continued)

Atoms

Natural charge

Atomic charges (Mulliken)

74 H

75 H

76 O

77 H

78 H

79 Cl

80 Cl

0.45694

0.44113

0.264997

0.246009

ꢁ0.94607

ꢁ0.493894

0.48413

0.278458

0.45230

0.246508

ꢁ0.85943

ꢁ0.745905

ꢁ0.79261

ꢁ0.726596

Conclusions

Table 17

The charge distribution calculated by the Mulliken and natural bond orbital (NBO)

methods of compound 4c.

Synthetic protocol of multiple synthesis for three 1-alkyl-1-

methylpiperazine-1,4-diium salts (AMPSs), where alkyl is benzyl

4a, n-octadecyl 4b, and methyl 4c, respectively, was evaluated

and described. The acid–base behavior of title AMPSs 4a–4c was

carried out, corresponding acid–base constants were obtained

and compared with data for similar piperazine derivatives. Single

crystals of AMPSs 4a–4c suitable for XRD-analysis were obtained,

analyzed and found results including molecular packing were dis-

cussed, as well. Results of vibrational spectral analysis, which were

obtained using both FT-IR and FT-Raman spectroscopy for 4a–4c,

are demonstrated. The complete vibrational assignments of

wavenumbers were made on the basis of a potential energy dis-

tribution. The complete vibrational assignments of wavenumbers

were made on the basis of potential energy distribution. The

HOMO and LUMO analysis was used to determine the charge trans-

fer within the molecules. The calculated ﬁrst hyperpolarizabilities

of AMPSs 4a–4c are 48.34, 57.77 and 123.41 times that of urea. The

molecular electrostatic potential map, second hyperpolarizability

studies are also reported. Further, the computed molecular electro-

static potential maps and the obtained values of Mulliken charges

as well as the results of HOMO and LUMO analysis contributed to

the explanation of the molecular packing in cells of AMPSs 4a–4c

found in their XRD analysis.

Atoms

Natural charge

Atomic charges (Mulliken)

1 I

2 Cl

3 N

4 N

5 C

6 H

7 H

8 C

9 H

10 H

11 C

12 H

13 H

14 C

15 H

16 H

17 C

18 H

19 H

20 H

21 C

22 H

23 H

24 H

25 H

26 H

ꢁ0.88553

ꢁ0.38245

ꢁ0.35096

ꢁ0.71225

ꢁ0.22430

0.27867

0.22014

ꢁ0.23297

0.25770

0.22918

ꢁ0.23207

0.22692

0.25123

ꢁ0.21904

0.22779

0.24283

ꢁ0.40454

0.22292

0.27224

0.22646

ꢁ0.41248

0.27164

0.22196

0.22638

0.28062

0.39992

ꢁ0.815655

ꢁ0.303691

ꢁ0.092515

ꢁ0.344350

ꢁ0.265066

0.276648

0.215783

ꢁ0.420873

0.260592

0.251592

ꢁ0.414709

0.244388

0.250797

ꢁ0.278377

0.231132

0.238476

ꢁ0.480381

0.216155

0.280938

0.218397

ꢁ0.501319

0.279483

0.232446

0.217417

0.214424

0.288270

Acknowledgements

The authors are thankful to the University of Antwerp, Belgium

and King Fahd University for Petroleum and Minerals, Saudi Arabia

for providing the computational facility to support this work, Dr.

Mulliken’s charges

The calculation of atomic charges plays an important role in the

application of quantum chemical calculations to molecular sys-

tems. Mulliken charges are calculated by determining the electron

population of each atom as deﬁned in the basis functions. The

charge distributions calculated by the Mulliken [79] and NBO

methods for the equilibrium geometry of title compounds are

given in Tables 15–17. The charge distribution of the molecules

have an important inﬂuence on the vibrational spectra. An

increased electron density (negative charge) can be found at Cl1,

Cl2, O3, N7 for 4a, at N1, N2 for 4b and at I1, C8, Cl2 for 4c.

Therefore it can be concluded that electrophilic substitution is

more preferred than nucleophilic substitution. Reactions based

on the attack of an electrophile are favoured especially at these

positions of the atoms of 4a, 4b and 4c.

ˇ

Richard Ševcík for FT-IR, FT-Raman spectra, Prof. Dr. Marek Necas

for XRD data, both the Department of Chemistry, Masaryk

Univerzity, and The Ministry of the Industry and Trade of the

Czech Republic for ﬁnancial support by Grant No. 2A-1TP/09.

Appendix A. Supplementary material

Supplementary data associated with this article can be found, in

the online version, at http://dx.doi.org/10.1016/j.molstruc.2015.03.

051.

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Article Doi

1-Alkyl-1-methylpiperazine-1,4-diium salts: Synthetic, acid-base, XRD-analytical, FT-IR, FT-Raman spectral and quantum chemical study

DOI: 10.1016/j.molstruc.2015.03.051

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