Synthesis, spectral characterization, thermal behaviour, antibacterial activity and DFT calculation on N'-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide and N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester

Article abstract of DOI:10.1016/j.saa.2015.02.055

Two new compounds N'-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide {Hbmshb (1)} and N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester {H₂mbhce (2)} have been synthesized and characterized with the aid of elemental analyses, IR, NMR and single crystal X-ray diffraction data. Compounds 1 and 2 crystallize in orthorhombic and monoclinic systems with space group Pna21 and P21/n, respectively. Inter and intra molecular hydrogen bonding link two molecules and provide linear chain structure. In addition to this, compound 2 is stabilized by CH...π and NH...π interactions. Molecular geometry from X-ray analysis, geometry optimization, charge distribution, bond analysis, frontier molecular orbital (FMO) analysis and non-linear optical (NLO) effects have been performed using the density functional theory (DFT) with the B3LYP functional. The bioefficacy of compounds has been examined against the growth of bacteria to evaluate their anti-microbial potential. Compounds 1 and 2 are thermally stable and show NLO behaviour better than the urea crystal.

Full text of DOI:10.1016/j.saa.2015.02.055

Accepted Manuscript
Synthesis, spectral characterization, thermal behavior, antibacterial activity and
DFT calculation on N’-[bis(methylsulfanyl) methylene]-2-hydroxybenzohy-
drazide and N’-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester
M.K. Bharty, R.K. Dani, S.K. Kushawaha, Om Prakash, Ranjan K. Singh, V.K.
Sharma, R.N. Kharwar, N.K. Singh
PII:
S1386-1425(15)00219-X
http://dx.doi.org/10.1016/j.saa.2015.02.055
SAA 13357
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
Received Date:
Revised Date:
Accepted Date:
21 October 2014
15 February 2015
16 February 2015
Please cite this article as: M.K. Bharty, R.K. Dani, S.K. Kushawaha, O. Prakash, R.K. Singh, V.K. Sharma, R.N.
Kharwar, N.K. Singh, Synthesis, spectral characterization, thermal behavior, antibacterial activity and DFT
calculation on N’-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide and N’-(4-methoxy benzoyl)-
hydrazinecarbodithioic acid ethyl ester, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
(2015), doi: http://dx.doi.org/10.1016/j.saa.2015.02.055
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REVISED MANUSCRIPT
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Synthesis, spectral characterization, thermal behavior, antibacterial
activity and DFT calculation on N'-[bis(methylsulfanyl) methylene]-2-
hydroxybenzohydrazide and N'-(4-methoxy benzoyl)-
hydrazinecarbodithioic acid ethyl ester
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M.K. Bhartya*, R.K. Dania, S.K. Kushawahaa, Om Prakashb, Ranjan K. Singhb, V. K. Sharmac, R.N. Kharwarc, N.K. Singha*
aDepartment of Chemistry, bDepartment of Physics, cDepartment of Botany, Banaras Hindu University, Varanasi, 221005, India.
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Abstract
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Two new compounds N'-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide
{Hbmshb (1)} and N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester
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{H2mbhce (2)} have been synthesized and characterized with the aid of elemental analyses,
IR, NMR and single crystal X-ray diffraction data. Compounds 1 and 2 crystallize in
orthorhombic and monoclinic systems with space group P n a 21 and P21/n, respectively.
Inter and intra molecular hydrogen bonding link two molecules and provide linear chain
structure. In addition to this, compound 2 is stabilized by CH∙∙∙π and NH∙∙∙π interactions.
Molecular geometry from X-ray analysis, geometry optimization, charge distribution, bond
analysis, frontier molecular orbital (FMO) analysis and non-linear optical (NLO) effects
have been performed using the density functional theory (DFT) with the B3LYP functional.
The bioefficacy of compounds have been examined against the growth of bacteria to
evaluate their anti-microbial potential. Compounds 1 and 2 are thermally stable and show
NLO behavior better than the urea crystal.
Keywords: Crystal structure, Hydrogen bonding, Antibacterial property, Thermal stability,
DFT calculation, NLO property.
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*Corresponding author. Tel.: +91 542 6702447, E-mail: mkbharty@bhu.ac.in (M.K. Bharty),
singhnk_bhu@yahoo.com (N.K. Singh).

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1. Introduction
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The chemistry of nitrogen-sulfur containing compounds is very interesting from the
viewpoint of their electrical conductivity, molecular magnetism, electrochemical, biological
and optoelectronic properties [1-5]. Metal complexes derived from N-aroyl
hydrazinecarbodiothioic alkyl esters or dithiocarbazic acid esters have been studied [6-10]
not only because of their intriguing coordination chemistry, but also because of their
pronounced biological activities against microbes, viruses and cancer cells [11-13]. The
potassium salt of N-(aroyl)-hydrazine carbodithioates are not very stable since they undergo
intramolecular cyclization with elimination of H2S forming 1,3,4-oxadiazole-2-thiones in the
presence of acid or base [14] or on complexation [15, 16]. The main interest in the synthesis
of esters is that they are much stable than the potassium salt and do not undergo cyclization
to form oxadiazole derivatives. These S-alkyl/aryl hydrazine carbodithioic acid esters form
complexes with a wide number of metal cations and show promising biological activity. A
survey of literature shows that several papers are available on the syntheses and spectral
characterization of substituted dithiocarbazates but there is very little work reported on the
dithioester of N-acyl hydrazide, RC(O)NH-NH-C(S)SR which contain a similar -NH-C(=S)
moiety as the S- alkyl esters of dithiocarbazic acid [11-13,17,18]. Following our interest in
the synthesis and structural studies of compounds containing the H-N-C=S moiety
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responsible for biological activity, we report herein the preparation of N'-
[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide (Hbmshb) and N'-(4-methoxy
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benzoyl)-hydrazine carbodithioic acid ethyl ester (H2mbhce) and their structural
characterization, microbicidal properties and DFT calculation.

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2. Experimental Section
2.1. Materials, Physical Measurements and method
Commercial reagents were used without further purification and all experiments were
carried out in open atmosphere. Methyl salicylate and methyl 4-methoxybenzoate (Sigma
Aldrich), CS2 (S D Fine chemicals, India) and KOH (Qualigens) were used as received.
Salicylic acid hydrazide was prepared by the reported method [19]. All the solvents were
dried and distilled before use following the standard procedure. Carbon, hydrogen, nitrogen
and sulfur contents were estimated on a CHN Model CE-440 Analyser and on an Elementar
Vario EL III Carlo Erba 1108. IR spectra were recorded in the 4000–400 cm-1 region as KBr
pellets on a Varian Excalibur 3100 FT-IR spectrophotometer. 1H and 13C NMR spectra were
recorded in DMSO-d6 on a JEOL AL300 FT NMR spectrometer using TMS as an internal
reference. Five human bacterial pathogens Salmonella typhi (MTCC 3216), Shigella flexneri
(ATCC 12022), Staphylococcus aureus (ATCC 25323), Aeromonas hydrophila (ATCC
7966) and Enterococcus faecalis were used to test the antibacterial activity of compounds 1
and 2. Commercial antibacterial drugs, streptomycin sulphate and neomycin sulphate
(Himedia) at the same concentrations (5-50 µg/disc) were used to compare effectiveness of
the test compounds.
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2.2.1 Synthesis of N2-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide (Hbmshb, 1)
Potassium N'-(2-hydroxy benzoyl)-hydrazine carbodithioate [K+(H2L)-] was prepared
by adding CS2 (1.5 mL, 20 mmol) dropwise to a suspension of salicylic acid hydrazide
(3.042 g, 20 mmol) in methanol (30 mL) in the presence of potassium hydroxide (1.12 g, 20
mmol) and the reaction mixture was stirred continuously for 30 min. A white solid

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[K+(H2L)-] which separated was filtered, washed with EtOH and dried. Methyl iodide (1.2
mL, 20 mmol) was added dropwise to the methanol suspension of the above freshly
prepared [K+(H2L)-] (2.660 g, 10 mmol) and stirred continuously for 2 h at room
temperature. The resulting yellow solution was concentrated and acidified with dilute
CH3COOH (20 % v/v) which yielded yellow precipitate of N2-[bis(methylsulfanyl)
methylene]-2-hydroxybenzohydrazide. This was filtered, washed with water and dried in
vacuo. The precipitate was dissolved in methanol filtered and kept for crystallization which
formed yellow crystals of compound 1. Yield: 60 %. M.p. 185 ºC. Anal. Calc. for
C10H12O2N2S2 (256.36): C, 46.83; H, 4.68; N, 10.91; S, 24.98. Found: C, 46.84; H, 4.70; N,
10.86; S, 25.02 %. IR (cm-1, KBr): ν(OH) 3301m, ν(NH) 3169m; ν(C=O) 1634s; ν(N–N)
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1069; ν(C=S) 828. H NMR (DMSO-d6; δ ppm): 11.80 (s, 1H, OH), 9.70 (s, 1H, NH), 7.5-
6.8 (m, 4H aromatic ring), 1.65 (s, 3H, -CH3). 13C NMR (DMSO-d6; δ ppm): 203.12 (>C-S),
163.98 (>C=O), 158.97 (C1), 134.41 (C3), 128.58 (C5), 119.69 (C6), 117.32 (C4), 115.27
(C2), 16.85 (C9, C10).
O
O
NH2
N
N2H4.H2O
H
OCH3
°C
Reflux 4 h,
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OH
OH
CS2
KOH
O
O
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2
N
SCH3
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5
H
8
CH3I
N
S
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4
3
N
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4
H
N
H
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8
1
SCH3
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3
OH
SK
1
OH
2
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Scheme 1: Synthesis of N2-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide

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2.2.2. Synthesis of N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester
(H2mbhce, 2)
[K+(H2L')-] was prepared as described above for the synthesis of potassium N'-(2-
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hydroxybenzoyl)-hydrazine
carbodithioate
[K+(H2L)-].
N'-(4-methoxy benzoyl)-
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hydrazinecarbodithioic acid ethyl ester (H2mbhce) was synthesized by adding ethyl iodide (1
mL, 10 mmol) dropwise to a methanol suspension of freshly prepared potassium [N'-(4-
methoxy benzoyl) hydrazine] carbodithioate [K+(H2L')-] (2.804 g, 10 mmol) and stirring the
reaction mixture for 2 h at room temperature. The resulting solution was filtered off and kept
for crystallization which yielded colorless crystals of compound 2 suitable for X-ray
analyses after 10 days. Yield: 50 %. M.p. 235 ºC. Anal. Calc. for C11H14N2S2O2 (270.36): C,
48.82; H, 5.18; N, 10.36; S 23.67. Found: C, 48.90; H, 5.22; N, 10.35; S, 23.59 %. IR (ν,
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cm-1, KBr): (NH) 3240m, (C=O) 1698s; (N-N) 1051; (C=S) 982. H NMR (DMSO-d6; δ
ppm): 11.75, 11.43 (s, 2H, NH), 7.96-6.98 (m, 4H aromatic ring), 3.34 (-OCH3), 2.58 (q,
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2H). 2.47 (t, 3H). C NMR (DMSO-d6; δ ppm): 187.81 (C9=S), 163.85 (C8=O), 162.42
(C2-O), 128.41 (C6, C4), 125.05 (C5), 114.42 (C3, C7), 55.40 (-OCH3), 39.26 (C10), 36.68
(C11).
O
O
NH2
CH3
N
H
N2H4.H2O
O
°
H3CO
Reflux 4h, 65 C
H3CO
KOH
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CS2
O
O
H
H
6
N
S
N
S
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5
8
N
H
8
N
H
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9
9
C2H5I
4
4
SCH2CH3
SK
H3CO
1
2
2
H3CO
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3
1
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Scheme 2: Synthesis of N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester

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3. Antibacterial assay
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The antibacterial assay was done according to the reported method with slight
modifications [20, 21]. The test compounds were dissolved in DMSO to a final
concentration of 5mg/mL. Sterilized Whatman no. 1 filter paper discs (5 mm) were
impregnated with different volume (1, 2, 4, 6, 8 and 10 µL) of compounds to get a final
concentration of 5, 10, 20, 30, 40 and 50 µg per disc. Sterilized paper disc loaded with the
10 µL of DMSO was taken as a control. The bacterial test pathogens were spread on fresh
Mueller Hinton Agar (MHA) plates with the help of cotton swabs to form an even lawn of
the test bacteria. The filter paper disc impregnated with the test compounds were placed on
the surface of the MHA plates seeded with test bacteria and the plates were incubated in a B.
O. D. incubator (Caltan-152, Narang Scientific Works, New Delhi, India) for 24 h at 37±2
ºC. The inhibition zone around each disc was measured after 24 h of incubation. Inhibitory
concentrations (IC50) of compounds 1 and 2 were determined using broth dilution method by
MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The test
compounds were dissolved in DMSO to a final concentration of 2 mg/ml. The test
compounds were diluted to various concentrations (2, 4, 8, 16, 32, 64, 100 µg/mL) in 5 mL
culture tube containing 2 mL Mueller-Hinton broth. One drop of exponentially growing
culture of test bacterium was inoculated in each concentration of compounds and incubated
at 37±2 ºC for 24 hours. A control was prepared using test bacterium and equal volume of
the DMSO (100 µL) in Mueller-hinton broth without test compound. After incubation
period, 200 µL MTT solution (5mg/ml) prepared in phosphate saline buffer (PBS) was
added to each vial and incubated at 37±2 ºC for one hour. Culture was centrifuged at 10,000

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rpm for 10 minutes and absorbance was observed at 570 nm. Minimum concentration of
compounds which were able to inhibit 50 % activity of bacteria is considered as IC50.
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4. Crystal structure determination
Crystals suitable for X-ray analyses of the compounds were grown at room
temperature. The crystal data were collected on an Oxford Gemini diffractometer equipped
with a CrysAlis CCD software using a graphite mono-chromated Mo Kα (λ= 0.71073 Å)
radiation source at 293 and 150 K for compounds 1 and 2, respectively. Multi scan
absorption correction was applied to the X-ray data collection for all the compounds. The
structure was solved by direct methods (SHELXS-08) and refined against all data by full
matrix least-square on F2 using anisotropic displacement parameters for all non-hydrogen
atoms. All hydrogen atoms were included in the refinement at geometrically ideal position
and refined with a riding model [22]. The MERCURY package and ORTEP-3 for Windows
program were used for generating structures [23, 24].
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5. Results and discussion
Two new compounds N'-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide (1) and
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N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester (2) have been prepared by
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the reaction of methyl/ethyl iodide with potassium N-(aroyl) hydrazinecarbodithioate. The
compounds are stable towards air and moisture and are soluble in methanol and ethanol
from which they have been crystallized to get single crystals. Schemes 1 and 2 depict the
formation of these compounds. The X-ray diffraction studies of compound 1 indicate that
carbodithioate [-NHNHC(S)S−] moiety has undergone thioenolization and the dithiol form
reacted with methyl iodide to yield bis(methylsulfanyl) methylene group and both sulfur are

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bonded with methyl group. In the case of compound 2, only one ethyl group is attached to
carbodithioate moiety without undergoing thioenolization.
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5.1. IR spectra
The IR spectrum of N2-[bis(methylsulfanyl) methylene]-2-hydroxy benzohydrazide
(1) in KBr shows absorptions (cm-1) due to the stretching modes of OH (3301), NH (3169),
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CH (2905), C=O (1634), N-N (1069) and C-S (828). The IR spectrum of N'-(4-methoxy
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benzoyl)-hydrazinecarbodithioic acid ethyl ester (2) shows absorptions (cm-1) due to the
stretching modes of NH (3240m), C=O (1698s), N-N (1051) and C=S (982) indicating the
presence of –C(O)NH-NH-C(S)- group [25].
5.2. 1H and 13C NMR spectra
The 1H NMR spectrum of Hbmshb (1) in DMSO-d6 shows two signals at δ 11.80 and
9.70 ppm due the phenolic (OH) and hydrazinic (NH) protons, respectively. The aromatic
protons appear as multiplet in the region of δ 7.5-6.8 ppm. The methyl protons are observed
at 1.65 ppm. The 13C NMR spectrum of Hbmshb shows signals at δ 203.12, 163.98, 158.97
ppm due to the C=S, C=O and C-O (phenolic) carbons, respectively. The phenyl ring
carbons appear at δ 134.41 (C3), 128.58 (C5), 119.69 (C6), 117.32 (C4), 115.27 (C2) ppm
while both methyl carbons are observed at δ 16.85 ppm. The 1H NMR spectrum of H2mbhce
in DMSO-d6 shows signals at δ 11.75, 11.43 and 3.34 ppm for the amide, thioamide and -
OCH3 protons, respectively. Four protons of the phenyl ring appear as multiplet in the range
δ 7.96-6.98 ppm and methylene and methyl protons of ethyl group appear at δ 2.58 and 2.47
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ppm, respectively. The C NMR spectrum of H2mbhce shows signals at δ 187.81, 163.85
and 162.42 ppm due to the C=S, C=O and C-O (methoxy phenyl) carbons, respectively. The
methylene and methyl carbons appear at δ 39.26 and 36.68 ppm, respectively while other

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methoxy phenyl carbons appear at δ 128.41 (C6, C4), 125.05 (C5), 114.42 (C3, C7) ppm.
The methoxy -OCH3 carbon is observed at δ 55.40 ppm.
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5.3 Thermal behaviour
The thermal stability of compounds 1 and 2 were studied by TG and DTA in the temperature
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range 30-950 ºC under a nitrogen atmosphere by controlling heating rate of 10 ºC per minute
using Perkin-Elmer simultaneous thermal analyzer (STA 6000). The thermograms (TG and
DTA curves) reveal that the compounds are stable up to 180 ºC and indicate the absence of
water molecule in crystalline phase [26]. Compounds 1 and 2 decompose in the temperature
range 190-700 and 240-600 ºC, respectively (Fig. 1a) and the weight loss could be due to
loss of organic moieties in the form of gaseous products through breaking of bonds. The
later stage is slower and corresponds to the oxidation or vaporization of intermediate
products in the temperature range 350-550 ºC indicating that thermolysis is exothermic in
nature. Heating of samples above 700 ºC leaves no residue. The stability of these
compounds are decided by the hydrogen bonding which is one of the most important non-
covalent interactions and plays a vital role in building the supramolecular structures, making
a great contribution to thermal stabilities. The presence of more intermolecular hydrogen
bonding along with NH∙∙∙π and CH∙∙∙π interactions, compound 2 is more stable and this may
be a probable reason that compound 1 decomposes earlier than compound 2.
Compound 1 has a lower thermal stability due to low dimensionality since it melts between
184-196 ºC and absence of any thermal change before this temperature range indicates that
sample restructuring does not take place before the degradation processes begins.
Comparing the TG and DTA curves, it is observed that the major weight loss process starts
after the melting temperature of the compounds. The DTA curve shows endothermic peak

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(at 190 ºC) just after exothermic peak (at 180 ºC) in compound 1 which implies melting with
slow decomposition, leading to volatilization upon heating further [27]. The DTA curve
indicates that compound 2 undergoes an irreversible endothermic transition at 230 ºC, where
melting begins and the endothermic peak represents the temperature at which the melting
terminates at its melting point of 235 ºC. The sharpness of the peak in DTA curve of
compound 1 indicates its good degree of crystallinity, purity and indicates that no phase
transition occurs before melting. The DTA curves of compounds 1 and 2 show that after 350
and 450 ºC (Fig. 1b), respectively slow oxidation of the products takes place.
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5.4. Antibacterial activity
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Antibacterial activity of compounds 1, 2 and commercial antibacterial drugs streptomycin
sulphate and neomycin sulphate were tested against five human bacterial pathogens
Salmonella typhi (MTCC 3216), Shigella flexneri (ATCC 12022), Staphylococcus aureus
(ATCC 25323), Aeromonas hydrophila (ATCC 7966) and Enterococcus faecalis. A clear
zone around the disc indicates the inhibitory activity of the compound on the organism. The
results are given in Table 1 which indicates that the inhibitions by compounds are lower as
compared to the standard drugs. The activity increases with increasing concentration of the
compound and compound 2 is more active as compared to compound 1. The highest zone of
inhibition (2.3 cm) was recorded against S. typhi at 40 and 50µg/disc and minimum zone of
inhibition was recorded in all cases at 5-20 µg/disc. Both the compounds are active against
E. faecalis at all concentration range. It is clear that the zone of inhibition area is somewhat
larger for compound 2 than 1. The increased activity of compound 2 may be due to the
presence of free HNCS moiety which is absent in compound 1 (Fig. 2a). Furthermore, free
HNCS moiety increases the delocalization of π-electrons over the molecule of compound 2

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and enhances the lipophilicity which leads to the breakdown of the permeability barrier of
the cell and thus retards the normal cell processes. The possible reason for the antibacterial
action of compound 2 may be that it binds to the membranes of microorganisms through the
hydrogen bonding with sulfur, prolonging the lag phase of the growth cycle and increasing
the generation time of the organisms so that each organism takes more time to complete cell
division. Although antibacterial activities of the compounds are lower as compared to the
standard drugs streptomycin sulphate and neomycin sulphate but these compounds could be
potentially used against weak bacterial pathogens.
Compound 2 is most effective against Shigella flexneri with IC50 value of 15.07 µg/mL
followed by Salmonella typhi (30.64 µg/mL), Enterococcus faecalis (30.80 µg/ml),
Staphylococcus aureus (37.23 µg/mL) and least effective against Aeromonas hydrophila
(91.38 µg/ml). Similar trend (Table 2) is also observed for compound 1 with 32.38 µg/ml
IC50 value for Shigella flexneri, 49.26 µg/mL for Salmonella typhi, 37.26 µg/mL for
Enterococcus faecalis, 37.98 µg/mL for Staphylococcus aureus and 105.41 µg/ml for
Aeromonas hydrophila. Fig. 2b shows that compound 2 is required in less amounts to inhibit
the growth of bacteria as compared to compound 1. Compound 2 shows impressively good
activity against Shigella flexneri and Salmonella typhi with about 2.1 and 1.6 fold less IC50
values, respectively than compound 1.
5.5. Crystal structure description of compounds 1 and 2
The molecular structures of compounds Hbmshb (1) and H2mbhce (2) have been
determined by single crystal X-ray diffraction data. The details of data collection, structure
solution and refinement are listed in Table 3. Molecular structure diagrams for compounds 1
and 2 with atom numbering schemes are shown in Figs.3 and 4, respectively. Selected bond

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lengths and angles are given in Tables 4 and 5. Weak intermolecular interactions are listed
in Tables 6 and 7. In compound 2, the C-S bond distances of 1.704(4) and 1.707(4) Å agree
well with those in related compounds, being intermediate between 1.82 Å for a C-S single
bond and 1.56 Å for a C=S double bond [28, 29] whereas for compound 1 the C-S bond
distances of 1.758(9) and 1.774(14) Å indicate their single bond character. The distances
and angles for Hbmshb (1) and H2mbhce (2) are close to those reported earlier [30, 31]. In
the solid state, compound 1 is stabilized via intermolecular C-H···O interaction between
carbonyl oxygen and CH hydrogen atoms of aromatic ring and O-H···O interaction between
hydroxyl hydrogen and carbonyl oxygen of a nearby molecule leading to the formation of
linear chain (Fig. 5). The structure of compound 2 is stabilized via intermolecular N-H···O
and C-H···O interactions occurring between carbonyl oxygen and hydrogen atoms of
hydrazine (-NH), -OCH3 and phenyl ring of a nearby molecule which leads to the formation
of linear chains, whereas the C-H···S interaction between thione sulfur and hydrogen atoms
of phenyl ring also contribute to the linear chain structure (Fig.6). The crystal structure of
compound 2 is also stabilized via NH∙∙∙π and CH∙∙∙π interactions between the π electrons of
phenyl ring and the hydrogens of hydrazine and methyl group, respectively.
5.6 Quantum chemical calculations
5.6.1. Optimization of geometry
All calculations and the geometry optimization for N2-[bis(methylsulfanyl) methylene]-2-
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hydroxybenzohydrazide (1) and N'-(4-methoxy benzoyl)-hydrazine carbodithioic acid ethyl
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ester (2) have been performed with Gaussian 03 and Gauss View 4.1 [32] program packages
using DFT method with functional B3LYP and basis set DFT/B3LYP/6-311G(d, p) [33, 34].
The input geometries for the DFT calculations were generated from single crystal X-ray

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data. The optimized geometrical parameters are listed in Tables 4 and 5. The optimized
geometries with charge distribution on atoms of molecules are shown in Fig. 7 and 8. The
optimized energy for compounds 1 and 2 are -1444.819 and -1484.147 a.u. respectively
which indicate that both compounds are stable. A slight disagreement in the bond lengths
and angles are due to the fact that the experimental results have been collected for the solid
phase and the theoretical calculations are done for the gas phase. In the solid state, the
existence of crystal field along with the intermolecular interactions connect the molecules
together, which results in the differences in bond parameters between the calculated and
experimental values. The charges on the carbonyl oxygen of compounds 1 and 2 have
almost comparable values whereas the charges on oxygen atoms of -OH and -OCH3 are -
0.412 and -0.338, respectively. On hydrazine moiety, the charge distributions on nitrogen
are in the range -0.352 to -0.122 for compound 1 and -0.337 to 0.226 for compound 2.
Considering the method and basis set used in the atomic charge calculation, the oxygen and
nitrogen atoms exhibit a negative charge which are donor atoms while the hydrogen atom
exhibits a positive charge which is an acceptor atom for the formation of hydrogen bonding
in the crystalline phase (Fig 7 and 12). The charge on the sulfanyl sulfur atom of compound
1 has a positive value, whereas the charge on the thioamide sulfur of compound 2 has a
negative value (-0.176) which is responsible for N-H···S hydrogen bonding, whereas no
such hydrogen bonding is observed in compound 1.
5.6.2. Molecular electrostatic potential and Contour maps:
The molecular electrostatic potential (MEP) mapped surfaces illustrate the charge
distributions of molecules three dimensionally which allow us to visualize variably charged
regions of a molecule. The charge distributions of the molecules give clear signature of the

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interactions of the molecules. The MEP mapped surface of the molecules are calculated by
DFT/B3LYP/6-311G(d,p) method at the 0.02 isovalues and 0.004 density values. The
molecular electrostatic potential (MEP) is a useful feature to study reactivity given that an
approaching electrophile will be attracted to negative regions. In the majority of the MEP,
the maximum negative region which is the preferred site for electrophilic attack are
indicated as red color while the maximum positive region which is the preferred site for
nucleophilic attack are symbolized in blue color. The importance of MEP lies in the fact that
it simultaneously displays molecular size, shape as well as positive, negative and neutral
electrostatic potential regions in terms of color grading. 3D plots of MEP for compounds 1
and 2 are shown in Figs. 9 and 10. The different values of the electrostatic potential at the
surface are represented by different colors. Potential increases in the order red < orange <
yellow < green < blue. The color code of these maps is in the range between -0.07931 to
+0.07931 a.u. for compound 1 and -0.05576 to +0.05576 a.u. for compound 2 where blue
indicates the strongest attraction and red, the strongest repulsion. Regions of negative V(r)
are usually associated with the lone pair on electronegative atoms. As can be seen from the
MEP map of compounds 1 and 2, the regions having the negative potential are over the
electronegative atom (oxygen/nitrogen) and the regions having the positive potential are
over the hydrogen atoms. The green areas cover parts of the molecule where electrostatic
potentials close to zero are the C-C, C-N and C-S bonds. The oxygen atoms have larger
negative potential value than the nitrogen atoms. The positive regions are localized on the
hydrogen atoms of CH3 and C2H5 groups and on the ring. From this result, we can say that
the hydrogen atoms indicate the strongest attraction and oxygen atoms indicate the strongest
repulsion.

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A contour map is a two-dimensional XY plot of a three-dimensional XYZ surface
showing lines where the surface intersects planes of constant elevation (Z). The contour
maps are also used to show lines of constant density or brightness, such as electrostatic
potentials [35]. The contour maps are calculated by DFT/B3LYP/6-311G(d,p) method at the
0.02 isovalues and 0.004 density values at same level of calculations of the MEP mapped
surface of the molecules. The electron rich red lines are around oxygen and nitrogen
whereas electron deficient region are shown by greenish-yellow lines. Both have similar
patterns of contour map as shown in Figs. 11 and 12.
5.6.3. Frontier molecular orbital (FMO) analysis
The HOMO energy characterizes the ability of electron transfer while the LUMO
characterizes the ability of electron acceptance, and the gap between HOMO and LUMO
characterizes the molecular chemical stability [36]. The HOMO-LUMO energy and the
energy gap (∆E) for the compounds have been calculated at DFT/B3LYP/6-311G(d,p) level
and the results are given in Table 8. 3D plots of the HOMO and LUMO for compounds 1
and 2 are shown in Fig.13. It can be seen that the HOMO orbital is mainly located at the
HNCS moiety of the compound as a result of the electron withdrawing effect of the OH and
OCH3 group, which in turn causes an increase in the LUMO electronic density as located on
the aromatic ring. Methoxy phenyl and hydroxyl phenyl rings do not make any contribution
to electron density of HOMO, whereas in LUMO the entire molecule contributes to form
frontier molecular orbitals. The value of the energy separation between the HOMO and
LUMO are 4.400627 and 4.575876 eV for compounds 1 and 2, respectively. The small
HOMO-LUMO energy gap means low excitation energy, a good stability and a low
chemical hardness for the compound. The electronic transition from the ground state to the

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excited state due to transfer of electrons from the HOMO to LUMO level is mainly a π∙∙∙π
transition. The chemical hardness of a molecule is defined by the formula [37]
η = {-EHOMO + ELUMO}/2
where EHOMO and ELUMO are the energies of the HOMO and LUMO molecular orbitals. The
value of η for compounds 1 and 2 are 2.2003135 and 2.287938 eV, respectively which
indicate that they are hard materials and compound 2 is harder than compound 1. The above
results indicate that compound 2 has better chemical activity and may effectively undergo
intramolecular charge transfer upon excitation. The above results show that smaller the
HOMO-LUMO energy gap, the larger the hyperpolarizability (see below) and compound 1
which has a substituted imine group (C=N double bond) may have potential applications in
the development of NLO materials [38].
5.6.4. Global reactivity descriptors
The chemical reactivity and site selectivity of the molecular systems have been determined
by the conceptual density functional theory [39]. Electronegativity (χ), chemical potential
(μ), global hardness (η), global softness (S) and electrophilicity index (ω) are global
reactivity descriptors and are highly successful in predicting global reactivity trends. On the
basis of Koopman’s theorem [36], global reactivity descriptors are calculated using the
energies of
Frontier molecular orbitals EHOMO, ELUMO and given by Eqs. (a) – (e) [40-44].
χ = ─ (EHOMO + ELUMO)/2 = (I + A)/2
μ = ─ χ = (EHOMO + ELUMO)/2 = ─ (I + A)/2
η = (─ EHOMO + ELUMO)/2 = (I ─ A)/2
(a)
(b)
(c)

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Where A and I are the ionization potential and electron affinity of the compounds
respectively. Electron affinity refers to the capability of a ligand to accept precisely one
electron from a donor. However, in many kinds of bonding viz. covalent hydrogen bonding,
partial charge transfer takes place. Softness is a property of a compound that measures the
extent of chemical reactivity and is the reciprocal of hardness.
S = 1/η
(d)
Recently, Parr et al. [45] have defined a new descriptor to quantify the global electrophilic
power of the compound as electrophilicity index (ω), which defines a quantitative
classification of the global electrophilic nature of a compound. Parr et al. have proposed
electrophilicity index (ω x) as a measure of energy lowering due to maximal electron flow
between donor and acceptor. They have defined electrophilicity index (ω) as follows
ω = μ2 S = μ2/η
(e)
This is positive and definite quantity and measures the stabilization in energy when the
system acquires an additional electronic charge (∆N) from the environment. The direction of
the charge transfer is completely determined by the electronic chemical potential of the
molecule because an electrophile is a chemical species capable of accepting electrons from
the environments; its energy must decrease upon accepting electronic charge. Therefore its
electronic chemical potential must be negative. When two molecules react, which one will
act as an electrophile (nucleophile) will depend upon higher (lower) value of electrophilicity
index. The high value of electrophilicity index shows that the compound is a strong
electrophile. The usefulness of this new reactivity quantity has been recently demonstrated
in understanding the toxicity of various pollutants in terms of their reactivity and site
selectivity [46]. The calculated value of electrophilicity index describes the biological

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activity for compounds. The energies of frontier molecular orbitals (EHOMO, ELUMO), energy
band gap (EHOMO ─ ELUMO), electronegativity (χ), ionization potential (A), electron affinity
(I), chemical potential (μ), global hardness (η), global softness (S) and global electrophilicity
index (ω) for 1 and 2 are listed in Table 8.
5.6.5. Non-linear optical effect
Non-linear optical (NLO) effects arise from the interactions of electromagnetic fields in
various media to produce new fields altered in phase, frequency, amplitude or other
propagation characteristics from the incident fields [47]. NLO is at the forefront of current
research because of its importance in providing the key functions of frequency shifting,
optical modulation, optical switching, optical logic, and optical memory for the emerging
technologies in areas such as telecommunications, signal processing, and optical
interconnections [48, 49].
Second harmonic generation test was performed in order to find the NLO property of the
grown crystal by using Kurtz-Perry technique [50]. Samples were prepared by crushing
crystalline powder of compounds between two transparent glass plates and then exposed to
picoseconds laser radiation at a wavelength of 1.907 μm. The second harmonic wave of 632
and 542 nm generated from the samples 1 and 2, respectively was detected by
photomultiplier tube after eliminating the pump light with a color filter and converted into
electrical signal which was displayed on an oscilloscope and the signal amplitude in volts
indicates the SHG efficiency of the samples. Urea crystals were used as the reference
material and it was found that the SHG efficiency of compounds 1 and 2 are 8.3 and 7.1
times that of urea.

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To support experimentally observed NLO property we have performed DFT
calculation. The calculations of the mean linear polarizability (αtot) and the mean first
hyperpolarizability (βtot) from the Gaussian output have been explained in detail previously
[51], and DFT has been extensively used as an effective method to investigate the organic
NLO materials [52]. The calculated total molecular dipole moment (μtot), linear
polarizability (αtot) and first-order hyperpolarizability (βtot) are 5.0301 D, 25.469 Ǻ3 and
4.7653 x 10-30 cm5/esu and 7.2718 D, 23.842 Ǻ3 and 3.942 x 10-30 cm5/esu for compounds 1
and 2, respectivily. Urea is one of the prototypical compounds used in the study of the NLO
properties of molecular systems. Therefore it was used frequently as a threshold value for
comparative purposes [37]. The values of μtot, αtot and βtot for urea are 3.53 D, 4.1446 Ǻ3 and
0.5883 X 10-30 cm5/esu, obtained at the 6-311G (d,p). Theoretically, the first-order
hyperpolarizability for compounds 1 and 2 are 8.1 and 6.7 times magnitude of urea. These
results indicate that the compounds are good candidate as NLO material and may be used for
application as non-linear optical material. Theoretical and experimental values are in
agreement with each other.
The presence of various types of hydrogen bonding interaction in compounds makes
the electron delocalization easier and decreases the value of the energy gap, as a result of
which the absorption bands in the electronic spectrum may shift to the visible region and
consequently, increases the nonlinear optical properties. The O-H···O and C-H···O
interactions in compound 1 and N-H···O and C-H···O in compound 2 play an important role
in making the structural unit, which enhances the overall electron transfer between donor
and acceptor groups. The O-H∙∙∙O hydrogen bond is known to have specific effects upon
crystal packing and plays a very important role in NLO contributions to the total

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nonlinearity [53]. The O-H∙∙∙O hydrogen bond consists of two types of bonds: the shorter O–
H bond and the longer H∙∙∙O bond, which are dependent on each other. Due to the presence
of above hydrogen bonding interaction, compound 1 shows more non linear optical effects
than compound 2 and may be used as optoelectronic material. The presence of hydrogen
bonds on optical nonlinearities of organic crystals has important implications in the
structural design. Calculated and experimentally observed results show us, in the process of
the material designing, that if we can optimize geometry of hydrogen bonds in crystals to the
optimum space directions, excellent NLO crystals may be obtained and this gives us a useful
clue that the crystal engineering should construct or optimize the space geometrical
configures of hydrogen bonds with the optimum bond directions, and their potential NLO
characteristics can be displayed up to the maximum.
6. Conclusion
This paper reports the syntheses, spectral, structural investigations and DFT calculations of
438
N2-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide (1) and N'-(4-methoxy
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benzoyl)-hydrazinecarbodithioic acid ethyl ester (2). In the solid state, both compounds are
stabilized by various types of hydrogen bonding such as C-H···O, N-H···O and C-H···S. In
addition, compound 2 involves CH∙∙∙π and NH∙∙∙π interactions. Antibacterial activity of
compounds 1 and 2 were tested against five human bacterial pathogens which showed that
the activity increases with concentration of the compounds. Compound 2 has better activity
than compound 1 but lower than the standard drugs, streptomycin sulphate and neomycin
sulphate. Compound 2 shows impressively good activity against Shigella flexneri and
Salmonella typhi with about 2.1 and 1.6 fold less IC50 values respectively than compound 1.
The geometries of the compounds are optimized at B3LYP density functional theory level

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which corroborate with the experimental data. The second harmonic generation (SHG)
efficiency of the crystals was obtained by classical powder technique and it was found that
the SHG efficiency of compounds 1 and 2 are 8.3 and 7.1 times that of urea. The NLO
properties of the thermally stable compounds are much greater than that of urea which
indicates that these compounds are good candidates as second-order NLO material. Due to
the presence of O-H∙∙∙O hydrogen bonding interaction, compound 1 shows more non linear
optical effects than compound 2 and may be used as optoelectronic material.
7. Acknowledgement
One of the authors R.K. Dani thanks UGC, New Delhi for the award of RGNF (SRF). Dr.
S.K. Kushawaha is thankful to the Department of Science and Technology, New Delhi,
India for the award of a Young Scientist Project (No. SR/FT/CS-110/2011).
8. Supplementary material
CCDC 942774 and 960471 contain the supplementary crystallographic data for compounds. These
data can be obtained free of charge from the Cambridge Crystallographic Data Center via
www.ccdc.cam.ac.uk/data_request/cif.
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Fig.1(a) Thermograms of compounds 1 and 2
Fig.1(b) DTA curve of compounds 1 and 2

Fig.2(a) Mechanism of antibacterial activity for compounds 1 and 2
Fig.2 (b) Inhibitory concentration (IC50) for compounds 1 and 2

Fig.3. Molecular structure of N2-[bis(methylsulfanyl) methylene]-2-hydroxybenzohydrazide (1)
Fig.4. Molecular structure of N'-(4-methoxy benzoyl)-hydrazinecarbodithioic acid ethyl ester (2)
Fig.5. O-H∙∙∙O and C-H∙∙∙O interactions leading to linear structure in Hbmshb (1)

Fig.6. C-H···O, N-H···O and C-H···S hydrogen bonding and NH∙∙∙π and CH∙∙∙π interactions in H2mbhce (2)
Fig.7. Optimize structure along with charge distribution on Hbmshb (1)
Fig.8. Optimise structure along with charge distribution on H2mbhce (2)