Synthesis, characterization, DFT calculations and catalase-like enzymatic activities of novel hexadentate Schiff base and its manganese complexes

Article abstract of DOI:10.1016/j.molstruc.2019.03.027

We reported the synthesis of the manganese(II) and manganese(III) complexes of a novel hexadentate Schiff base ligand (HBME) (1) obtained from the condensation of triethylenetetramine and 2 equiv. of 1-(biphenyl)-2-hydroxyimino-2-(morpholino)-1-ethanone.

Full text of DOI:10.1016/j.molstruc.2019.03.027

Accepted Manuscript
Synthesis, characterization, DFT calculations and catalase-like enzymatic activities of
novel hexadentate schiff base and its manganese complexes
Murat Karakoç, Bülent Dede, Mukadder Erdem Tunçmen, Fatma Karipcin
PII:
S0022-2860(19)30294-7
DOI:
https://doi.org/10.1016/j.molstruc.2019.03.027
MOLSTR 26296
Reference:
To appear in: Journal of Molecular Structure
Received Date: 8 November 2018
Revised Date: 1 March 2019
Accepted Date: 8 March 2019
Please cite this article as: M. Karakoç, Bü. Dede, M. Erdem Tunçmen, F. Karipcin, Synthesis,
characterization, DFT calculations and catalase-like enzymatic activities of novel hexadentate schiff
base and its manganese complexes, Journal of Molecular Structure (2019), doi: https://doi.org/10.1016/
j.molstruc.2019.03.027.
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SYNTHESIS, CHARACTERIZATION, DFT CALCULATIONS AND
CATALASE-LIKE ENZYMATIC ACTIVITIES OF NOVEL
HEXADENTATE SCHIFF BASE AND ITS MANGANESE COMPLEXES
Murat KARAKOÇa, Bülent DEDEb , Mukadder ERDEM TUNÇMENc, Fatma
*
KARİPCİNa
aNevşehir Hacı Bektaş Veli University, Department of Chemistry, Nevşehir, Turkey
bSüleyman Demirel University, Department of Chemistry, Isparta, Turkey
cSüleyman Demirel University, Experimental and Observational Student Research and App.
Center, Isparta, Turkey
*e-mail: bulentdede@sdu.edu.tr
Tel: +90 246 2114153

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ABSTRACT
We reported the synthesis of the manganese(II) and manganese(III) complexes of a novel
hexadentate Schiff base ligand (HBME) (1) obtained from the condensation of
triethylenetetramine and 2 equiv. of 1-(biphenyl)-2-hydroxyimino-2-(morpholino)-1-
ethanone. Hexadentate Schiff base ligand reacted with manganese(II) perchlorate or
manganese(III) acetate and sodium azide, to give rise to a series of mono and dinuclear
complexes [Mn(BME)2tren)] (2), [Mn2(BME)2tren(N3)2] (3) and [Mn2(BME)2tren(N3)4] (4).
Synthesized molecules were characterized by elemental analyses, ICP-MS, spectroscopic
studies, thermal analyses, molar conductivity and magnetic susceptibility measurements. The
quantum chemical calculations of the HBME and complexes (2-4) were performed in the
ground state using the DFT of B3LYP level with 6-311G(d,p) and LanL2DZ basis sets,
1
respectively. H- and 13C-NMR chemical shifts were calculated by using the gauge
independent atomic orbital (GIAO) method and the electronic properties such as HOMO-
LUMO energies were determined by the time-dependent DFT approach. The calculated
spectroscopic values for the HBME were in very good agreement with experimental ones.
Furthermore, catalytic activity of the complexes for the disproportionation of hydrogen
peroxide was also investigated in the presence of 1-methylimidazole. All the complexes
displayed catalytic ability for the disproportionation of H2O2 significantly, but the activities of
the (3) and (4) were relatively higher than the other molecules.
Keywords: Schiff base, manganese, dinuclear complex, DFT, catalase-like activity

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1. INTRODUCTION
Manganese is known to be an essential element in many biological systems and a catalytic
component of several enzymes, including catalase. Its oxidation-reduction chemistry is
especially important for the electron-transfer reactions of mitochondrial superoxide
dismutase, bacterial catalases and photosystem II in green plant photosynthesis. Catalase, one
of the three major sensitive protective enzymes in living organisms, exists in almost all
aerobically respiring organisms. It protects biological systems against oxidative damage
caused by hydrogen peroxide generated during aerobic metabolism through bioelectronic
reduction of molecular oxygen, the latter being linked to a variety of pathological
consequences such as aging, diabetes and cancer [1, 2].
Recently, Schiff base manganese complexes have been of great interest because of the
remarkable structural variety and the potential applications of these compounds in
magnetochemistry, catalysis and bioinorganic chemistry [3-6]. In the area of bioinorganic
chemistry, these complexes are very well studied because these species may be used as
synthetic models of the active site of various proteins and enzymes such as catalases [1,2],
catechol oxidase [4], superoxide dismutase [7]. The behaviour of these manganese complexes
is mainly dependent on the structure and coordination mode of the ligands in addition to the
oxidation state of manganese [6].
In this work novel hexadentate Schiff base ligand and its neutral mononuclear and dinuclear
complexes containing bridging azide ligands were synthesized and structurally characterized.
1
Molecular geometry, vibrational frequency, H- and 13C-NMR chemical shifts, HOMO–
LUMO, molecular electrostatic potential (MEP) and potential energy surface (PES) studies

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were performed using Density Functional Theory (DFT). The disproportionation of hydrogen
peroxide by the complexes (2-4) was also discussed.
2. EXPERIMENTAL
2.1. Materials and Physical Measurements
All chemical reagents and solvents were purchased from Merck or Aldrich and used without
further purification. The elemental analyses and metal contents were performed by using on a
LECO 932 CHNS analyser and a Perkin Elmer NexION 300D ICP-Mass Spectrometer. The
room temperature attenuated total reflection Fourier transform infrared (FT-IR ATR)
spectrum of the compound was registered using a Perkin Elmer Spectrum 100 FT-IR
1
13
spectrometer (4000-650 cm−1). H-NMR and C-NMR spectra were recorded on a Bruker
AVANCE III 400 FT-NMR spectrometer, using CDCl3 as a solvent and TMS as an internal
standard. Melting points were determined using an EZ-Melt melting point apparatus.
Magnetic susceptibility measurements were carried out using an Alfa Magnetic Susceptibility
Balance at room temperature. The molar conductivities were obtained on a WTW COND
3110 conductivity meter. Thermogravimetric analyses were carried out on a Shimadzu TG
DTA 60 thermal analyzer. The experiments were performed in dynamic nitrogen atmosphere
(20 mLmin-1) with a heating rate of 10oCmin-1 in temperature range 20-1000oC
2.2. Synthesis of ligand, HBME (1)
1-(Biphenyl)-2-hydroxyimino-2-chloro-1-ethanone was prepared according to literature [8].
Firstly, 1-(Biphenyl)-2-hydroxyimino-2-chloro-1-ethanone (1.5 mmol; 0.389 g) was dissolved
in EtOH (40 mL) and the mixture was cooled to -5oC. Morpholine (3 mmol; 0.26 mL) was
dissolved in EtOH (5 mL) and added dropwise to the first solution with cooling. After that
period, the reaction mixture was stirred 2 h at the same temperature. Then it was allowed to

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stir at ambient temperature for 2 h and diluted 100 mL distilled water. The resulting
precipitate was filtered and then recrystallized from ethanol-water (1:4). The product was
filtered off, washed with aqueous sodium bicarbonate (1%), distilled water, ethanol and dried
on P2O5.
(1): Yellow powder; yield: 88%; m.p.: 125oC. Anal. Calc. for C18H18N2O3 : C, 69.67; H, 5.84;
N, 9.03. Found: C, 69.55; H, 5.84; N, 9.00; 1H-NMR (CDCl3, ppm): Theo. Calc. 3.44(m, 4H,
N-CH2); 3.79 (m, 4H, O-CH2); 7.60-8.69 (m, 9H, Ar); 12.04 (s, 1H, NOH). Found: 3.41(m,
4H, CH2); 3.71 (m, 4H, CH2); 7.45-8.03 (m, 9H, Ar); 8.49 (s, 1H, NOH); 13C-NMR (CDCl3,
ppm): Theo. Calc. 192.12 (CO); 155.67 (C=NOH); 130.97-154.97 C (Arom); 49.40-65.52
ppm C (Aliph). Found: 188.25 (CO); 147.36 (C=NOH); 127.12-146.58 C (Arom); 46.67-
48.94 ppm C (Aliph); FT-IR (cm-1): Theo. Calc. 3304 (OH) 3083 (CH arom), 2995, 2875 (CH
aliph), 1682 (C=O), 1574 (C=N), 1248 (C-O), 989 (NOH) Found: 3278 b (OH) 3047 w (CH
arom), 2959, 2858 w (CH aliph), 1661s (C=O), 1598 s (C=N), 1264 m (C-O), 981 s (NOH)
(b, broad; s, strong; m, medium; w, weak).
2.3. Synthesis of complexes, (2-4)
Caution: Although no problems were encountered in the present work, perchlorates are
potentially explosive and should be treated in small quantities with care.
Synthesis of [Mn(BME)2tren)] (2)
A methanolic solution (30 mL) of HBME (2 mmol, 620 mg) was added dropwise to a
methanolic solution (10 mL) of triethylenetetramine (1 mmol, 0.15 mL). The yellowish
mixture was stirred at reflux temperature for 2 h. Then, a solution of Mn(CIO4)2.6H2O (1
mmol, 360 mg) in methanol (10 mL) was added to the mixture and stirring was continued for

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another 1 h and filtered. The powder product was washed with distilled water, ethanol and
dried on P2O5.
(2): Black-brown powder; yield: 45%; m.p.: 189oC. Anal. Calc. for C42H48N8O4Mn: C, 64.36;
H, 6.16; N, 14.29; Mn, 7.00. Found: C, 64.00; H, 5.89; N, 14.00; Mn, 6.50. ΛM (DMF
solution, ꢀ –1 cm2 mol–1): 15; µeff =5.55 B.M.; FT-IR (cm-1): 3309 b (NH) 3027 w (CH arom),
2918 w (CH aliph), 1584 s (C=N), 1277 m (C–O), 1021 s (NOH).
Synthesis of [Mn2(BME)2tren(N3)2] (3)
A methanolic solution (30 mL) of HBME (2 mmol, 620 mg) was added dropwise to a
methanolic solution (10 mL) of triethylenetetramine (1 mmol, 0,15 mL). The yellowish
mixture was stirred at reflux temperature for 2 h. Then, a solution of Mn(CIO4)2.6H2O (2
mmol, 720 mg) in methanol (10 mL) was added to the mixture. After 2 h of stirring, NaN3 (2
mmol, 130 mg) dissolved in distilled water (2 mL) was added dropwise, and the mixture
turned black. After 2 h of stirring, the precipitate was filtered, the powder product was washed
with distilled water, ethanol and dried on P2O5.
(3): Brown powder; yield: 48%; m.p.: 285oC. Anal. Calc. for C42H48N14O4Mn2 : C, 54.71; H,
5.24; N, 21.26; Mn, 11.91. Found: C, 54.12; H, 4.97; N, 21.00; Mn, 11.61. ΛM (DMF
solution, ꢀ –1 cm2 mol–1): 6.2; µeff =6.36 B.M.; FT-IR (cm-1): 3278 b (NH) 3024 w (CH
arom), 2961 w (CH aliph), 2057 s (N3), 1587 m (C=N), 1270 m (C–O), 1021 m (NOH).
Synthesis of [Mn2(BME)2tren(N3)4] (4)
Complex (4) was prepared by addition dropwise of a methanolic solution (10 mL) of
triethylenetetramine (1 mmol, 0,15 mL) in methanolic solution (30 mL) of HBME (2 mmol,

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620 mg). The resulting mixture was stirred at reflux temperature for 2 h. Then, a solution of
Mn(CH3COO)3.2H2O (2 mmol, 536 mg) in methanol (15 mL) was added to the mixture. After
2 h of stirring, NaN3 (4 mmol, 260 mg) dissolved in distilled water (2 mL) was added
dropwise. After 2 h of stirring, the precipitate was filtered, the powder product was washed
with distilled water, ethanol and dried on P2O5.
(4): Brown powder; yield: 40%; m.p.: 260oC. Anal. Calc. for C42H48N20O4Mn2 : C, 50.14; H,
4.80; N, 27.84; Mn, 10.92. Found: C, 50.04; H, 4.00; N, 27.50; Mn, 10.48. ΛM (DMF
solution, ꢀ –1 cm2 mol–1): 6.6; µeff =4.31 B.M.; FT-IR (cm-1): 3239 b (NH) 3031 w (CH
arom), 2930 w (CH aliph), 2050 s (N3), 1587 m (C=N), 1268 m (C–O), 1020 m (NOH).
2.4. Computational Studies
All calculations were performed using the Gaussian 09 program [9]. Visualizations were done
with the GaussView 5.0.9 program [10]. Geometry optimization and frequency calculations
were performed using Becke's B3LYP [11-13] function, which consists of a three-parameter
exchange function (B3) and a Lee-Yang-Parr correlation function (LYP) with 6-311G(d,p)
basis set. In order to prevent the systematic errors the computed vibrational wavenumbers
were scaled as 0.9682 for frequencies higher than 1700 cm-1 and 1.0119 for frequencies less
than 1700 cm-1 for B3LYP/6-311G(d,p) basis set [14]. Molecular structural calculations of the
complexes (2-4) were performed in gas phase at DFT/B3LYP level with LanL2DZ basis set
which stands for ‘‘Los Alamos National Laboratory 2-Double–Z’’ [15,16]. Electronic
properties and HOMO-LUMO orbitals of the HBME and its metal complexes were studied
1
13
using TD-DFT/B3PW91 with same basis sets. H- and C-NMR chemical shift calculations
were performed using the GIAO method [17-19].

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2.5. Studies on Catalase-like Function
The catalytic activities of ligand (1) and its complexes (2-4) towards the disproportionation of
hydrogen peroxide were investigated by measuring the volume of evolved oxygen during the
course of the reaction [20]. Volumetric measurements of evolved dioxygen during the
reactions of the compounds with H2O2 were carried out as follows: A 50 mL three-necked
round-bottom flask containing a suspension of the complexes (0.005 mmol solid sample) in
DMF (10 mL) was placed in a water bath (25°C). One of the necks was connected to a burette
and the others were stoppered by a rubber septum. While the solution was stirring, H2O2 (1.33
mmol, 0.150 mL) was injected into it through the rubber septum using a microsyringe.
Volumes of evolved dioxygen were measured at 1 min time intervals by volumometry. In
cases where 1-methylimidazole (50 mg) was added this was introduced into the reaction
vessel before the addition of H2O2 (in the absence of the 1-methylimidazole the complexes
were either inactive or very weak catalysts for this reaction).

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3. RESULTS AND DISCUSSION
Novel 1-(Biphenyl)-2-hydroxyimino-2-(morpholino)-1-ethanone (HBME) ligand was
synthesized in three steps. The synthetic plan for the synthesis of the HBME is given in
Scheme 1. Mono and dinuclear manganese complexes were prepared by reaction of HBME
with triethylenetetramine (tren), Mn(CIO4)2.6H2O [for complexes (2) and (3)],
Mn(CH3COO)3.2H2O [for complex (4)] and NaN3. The complexes were insoluble in water
and common organic solvents but showed maximum solubility in DMF and DMSO at room
temperature. The complexes were thermally stable at least up to about 200oC. Attempts to
isolate crystals suitable for X-ray diffraction were unsuccessful. Therefore, elemental
analyses, ICP-MS, spectroscopic, molar conductivity, thermal and magnetic susceptibility
techniques were employed in order to determine the structural characteristics of the
complexes. The analytical data of the complex (2) indicated 1:2 metal-ligand stoichiometry
whereas this ratio was 2:2 in (3) and (4) (Figs. 2-4). The values of the molar conductance
in10-3 M DMF solutions were in the range 6.2-15 ohm-1cm2mol-1, suggesting a non-
electrolytic nature for these complexes [21].
Scheme 1. Synthetic plan for the synthesis of the HBME

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3.1. 1H- and 13C-NMR spectra
1
The H- and 13C-NMR data of the ligand (HBME) were recorded in CDCl3 and used as
important evidence for the assigned structures. 1H- and 13C-NMR chemical shift values of the
HBME were also calculated at B3LYP/6-311G(d,p) level of theory. The experimental and
calculated chemical shifts, expressed in ppm downfield from tetramethylsilane, are given in
Experimental section and these NMR spectra are also given in Figs. S1 and S2 comparatively.
The 1H-NMR spectrum of the HBME showed a singlet at 8.49 ppm assigned for oxime NOH
proton. This proton (H27), which was adjacent to two electronegative atoms such as nitrogen
and oxygen, was calculated in a slightly lower field (cal. 12.04 ppm) than the experimental
result. A multiplet observed in the range 7.45-8.03 ppm may be attributed to the aromatic ring
protons [22-24]. The calculated chemical shift values in aromatic rings were observed at the
interval 7.60-8.69 ppm. The chemical shifts of N-CH2 (4H) and O-CH2 (4H) of the
morpholino ring were observed at 3.41/3.44 ppm (exp./cal.) and 3.71/3.79 ppm (exp./cal.),
respectively [25-27].
1
The H-NMR spectral data of the ligand were supported by the 13C-NMR spectra. The
chemical shift which belongs to the carbonyl carbon atom (C=O) was obtained at 188.25 ppm
while shift was observed at 192.12 ppm in theoretical spectrum. The signal for the carbon
atom (C=NOH) bonded to the oxime group was observed at 147.36 ppm, which also confirms
the structure of the ligand. Calculated value of the oxime carbon atom (C23) by DFT was
observed at 155.67 ppm. The chemical shift values for the carbon atoms of the aromatic rings
13
were found as 127.12-146.58/130.97-154.97 ppm (exp./cal.), respectively. In the C-NMR
spectrum of the HBME, the signals between 46.67 and 48.94 46 were attributed to carbon
atoms of the heterocyclic morpholino ring which were calculated as 49.40-65.52 ppm. All the

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protons and carbons were found to be in their expected regions and in good agreement with
values previously reported [22,24,27,28]. The results strongly suggest that the proposed
oxime ligand was formed. Because of the paramagnetic nature of the complexes, their 1H and
13C NMR spectra could not be obtained.
3.2. FT-IR spectra
The experimental and simulated at B3LYP/6-311G(d,p) IR spectra of the HBME are
presented in Fig. S3. The significant wavenumbers obtained from these spectra are given in
Experimental section. The IR spectra of the free ligand and their complexes exhibited various
bands in the 4000-650 cm–1 region. The FT-IR spectrum of the oxime ligand showed medium
band at 3278 cm-1, assignable to ν(OH) of oxime group; the broad nature of these bands and
their low wavenumbers suggested the presence of hydrogen bonding [29]. The corresponding
calculated value was 3304 cm-1 which was quite consistent with the experimental value. The
C=O vibrations for the ligand was observed as sharp band at 1661 cm-1. The same vibration
appears in the theoretical calculations at 1682 cm-1. In the IR spectrum of the ligand, the
stretching vibration of C=N was observed at 1598 cm-1 [30-32] and the stretching vibration of
N-O was observed at 981 cm-1 as reported for similar ligands [33-35]. Their calculated
wavenumbers were found as 1574 and 989 cm-1, respectively.
The IR spectra of the HBME (1) and its metal complexes (2-4) provided information about
the metal-ligand bonding. The broad stretching bands due to the -OH group of the free ligand
did not appear in the IR spectra of the complexes. This means that the Schiff base was
deprotonated and act as dianionic ligand. The ν(N-O) stretching frequencies were shifted to
1020-1021 cm−1 in the complexes. In addition, the bands observed in the 3209-3279 cm-1

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range of the complexes were due to the stretching vibrations of the N-H bond in the
triethylenetetramine group of the structure.
The strong band occurred at 1661 cm-1 resulting from the streching vibration of the C=O
bond in the HBME ligand was disappeared with the addition of triethylentetraamine. Instead
of this band, ν(C=N) of Schiff base were observed in the 1584-1587 cm-1 range. The presence
of streching vibrations of the C=N bond in the spectra of the complexes showed that
triethylenetetramine was bound to the ligand and the condensation reaction was completed.
-
While the peaks belonging to N3 group were observed between 2050-2064 cm-1 in the
complexes (3) and (4), no peaks were observed in the FT-IR spectrum of complex (2) in this
region [36,37]. The experimental and theoretical wavenumbers of N-O bond in the oxime
group of the HMBE were found to be 981 and 989 cm-1, respectively. The experimentally
observed band was shifted to high value after the formation of the complex. This showed that
the N-O group of oxime group also participated in the coordination [38-40].
When the FT-IR spectra of the ligand and its metal complexes were evaluated, the
disappearance of some bands, the appearance of new bands and the shifting of the bands
showed that the HBME ligand was synthesized and Mn(II) and Mn(III) ions participated
coordination with the ligand. In addition, the data obtained from the spectra of the compounds
were found to be consistent with the values of similar compounds in the literature [36-42].
3.3. Magnetic studies
The room temperature magnetic moments of the complexes showed that all of the complexes
were paramagnetic. Measurements on the complex (2) revealed a room temperature magnetic
moment of 5.55 B.M., which was compatible with a high-spin d5 system. Such behavior is

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typical of this class of compound. The measured magnetic moments of the dinuclear
manganese(II) (3) and manganese(III) (4) complex was found to be as 6.36 and 4.31 B.M.,
respectively. Magnetic susceptibility measurements showed that these complexes were five
and four-electron paramagnetics, which corresponds to the +2 and +3 oxidation states of
manganese (high-spin d5 and d4) in these complexes. This values were in agreement with a
spin value of 5.91 and 4.90 B.M. for the Mn(II) and Mn(III) complexes, respectively [43-45].
3.4. Thermal studies
In thermogravimetric analyses (TGA) the change in weight of a complex was recorded as a
function of temperature during heating. The TGA curve was also supported by the derivative
thermogravimetry (DTG) curves. All the complexes showed a gradual mass loss indicating
decomposition by fragmentation with an increase in temperature (Figs. 1,S4,S5). The
complexes were decomposing in a gradual manner rather than with the observed sharp
decomposition above 230oC, which may be due to fragmentation and thermal degradation of
the organic moiety. Dinuclear manganese complexes showed residues not conforming to the
corresponding a metallic residue such as metal oxides or metallic manganese, even at 1000oC,
indicating that the decomposition of the organic moiety remains incomplete even at this
temperature. In the case of the mononuclear Mn(II) complex, the molecule showed mass loss
in a gradual manner above 254oC. The continuous loss of weight was observed up to 665-
900oC; after that the weight of the product of the complex was remained constant. The final
weight losses in these cases were agreed with the formation of the respective MnO2 (Fig. 1).

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Figure 1. 4. TGA thermogram of complex (2) at a scanning rate of 10 oCmin-1.
N
HN
NH
N
Mn
N
N
N
N
O
O
O
O
Figure 2. Proposed structure of the [Mn(BME)2tren)] (2) complex

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Figure 3. Proposed structure of the [Mn2(BME)2tren(N3)2] (3) complex

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Figure 4. Proposed structure of the [Mn2(BME)2tren(N3)4] (4) complex
3.5. Computational Studies
3.5.1. Geometry Optimization
Geometry optimization of the HBME was performed using B3LYP functional with 6-
311G(d,p) basis set in gas phase. The optimized and numbered geometry of the HBME is
shown in Fig. 5. Selected calculated bond lengths, bond angles and dihedral angles are given
in Table 1. The calculated bond length of C1-C2 in the benzene ring was 1.391 Ao. The C5-
C12 (1.483 Ao) bond between the two benzene rings in biphenyl was observed longer than the
carbon-carbon bond in the aromatic rings. The lengths of the C15-C22 bond between the
biphenyl-carbonyl groups and C22-C23 bond between carbonyl-oxime groups were found to
be 1.490 Ao and 1.504 Ao, respectively, which were in agreement with the lengths of the
single bonds. The C23-N24 double bond length was calculated to be shorter (1.298 Ao) than
the single bond as expected.

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Figure 5. Optimized geometric structure of the HBME computed at B3LYP/6-311G(d,p)
level
If all four neighbouring atoms lie on same plane in a molecule, the dihedral angle is equal to
0° or 180°. The calculated value for the C6-C5-C12-C13 dihedral angle was found as 141.1
Ao. This result revealed that two benzene ring in the biphenyl moiety of the HBME weren’t
lying in the same plane. Furthermore, dihedral angles C22-C23-N28-C29 and C31-O37-C34-
C30 were computed as -58.7 Ao and -59.3 Ao, respectively. The molecular structure of HBME
showed that the morpholino ring was deviated from carbonyl and oxime carbon atom planes.
On the other hand, it was found that morpholino ring was not in linear geometry.

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Table 1. Some selected calculated bond lengths (Å), bond and dihedral angles (o) for the
HBME computed at B3LYP/6-311G(d,p) level
HBME (1)
Bond lengths (Å)
C1-C2
1.391
1.084
1.483
1.388
1.081
1.490
1.232
1.504
1.298
1.367
0.981
1.404
1.530
1.092
1.092
1.421
1.429
C3-H9
C5-C12
C16-C17
C16-H18
C15-C22
C22-O25
C22-C23
C23-N24
N24-O26
O26-H27
C23-N28
C30-C34
C29-H33
C34-H39
C31-O37
C34-O37
Bond angles (o)
C3-C1-C2
120.2
120.2
118.3
121.0
121.1
117.9
120.8
118.5
124.1
119.4
H9-C3-C4
C2-C5-C6
C5-C12-C13
C5-C12-C17
C13-C12-C17
C13-C14-C15
C14-C15-C16
C16-C15-C22
C15-C22-O25

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C15-C22-C23
C23-N24-O26
N24-O26-H27
C23-N28-C29
C30-C34-O37
122.6
120.3
107.5
117.1
110.6
Dihedral angles (o)
-0.2
C3-C1-C2-C5
H9-C3-C4-C6
-179.9
C6-C5-C12-C13
141.1
-0.9
C12-C17-C16-C15
C16-C15-C22-O25
C14-C15-C22-C23
C23-N24-O26-H27
C22-C23-N28-C29
C23-N28-C30-C34
C31-O37-C34-C30
156.2
164.6
15.8
-58.7
87.9
-59.3
The molecular geometries of the complexes (2-4) were also optimized in gas phase using DFT
based B3LYP method along with LanL2DZ basis set. The numbering schemes for the (2), (3)
and (4) are given in Figs. 6, 7 and 8, respectively. Hydrogen atoms were neglected in order to
allow the representation of the complexes to be simple. Some selected calculated bond
lengths, bond angles and dihedral angles are also given in Table 2.

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Figure 6. Optimized geometric structure of the complex (2) computed at B3LYP/LanL2DZ
level
Figure 7. Optimized geometric structure of the complex (3) computed at B3LYP/LanL2DZ
level

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Figure 8. Optimized geometric structure of the complex (4) computed at B3LYP/LanL2DZ
level
A slight elongation in C5-C12, C23-N24, C23-N28 bond lengths and a slight shortening in
C24-O26 bond length was observed in all three complexes after the coordination was
completed. In addition, it was observed that the C23-N24-O26 bond angle of the oxime group
increased slightly after the oxygen atom of this group was coordinated with manganese ions.
N22 atom was found in the equatorial position while the O54 atom was found in the axial
position of the Mn(II) ion in complex (2). The calculations showed that N22-Mn55-O54 and
O53-Mn55-N28 bond angles were 89.8 and 171.2o, respectively. The calculated bond length
and bond angle values for the metal complex (2) indicated the octahedral geometry around the
Mn(II) ion. The four equatorial positions of Mn(II) ion were occupied by amine nitrogen,
oxime oxygen and two imine nitrogen atoms, while two axial positions were occupied by
amine nitrogen and oxime oxygen atoms.

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N22-Mn55-O53, N25-Mn55-N60, N31-Mn56-O54 and N28-Mn56-N60 angles were
calculated to be close to 90o degrees in complex (3). Mn55 and Mn56 ions were found in
distorted square pyramidal coordination and surrounded by five atoms (imine nitrogen, oxime
oxygen, amine nitrogen and two azide nitrogen atoms). According to the calculated bond
angles around the Mn(II) in complex (3), it was found that one of the azide molecule lay in
the perpendicular plane. Furthermore, the Mn55-N59-Mn56-N60 dihedral angle of the four-
membered ring formed by Mn55 and Mn56 ions and two azide bridges was calculated to be
26.4o. This value showed that the atoms of the four-membered ring deviated slightly from
linearity and weren’t lay in the same plane.
The complex (4) was six coordinated with slightly distorted pentagonal pyramidal
environment around the Mn(III) ions. The Mn(III) was coordinated with amine nitrogen,
imine nitrogen, oxime oxygen and three azide nitrogen atoms. Amine nitrogen atom was
coordinated perpendicular to the Mn(III), while all other atoms were in the equatorial position
of the metal ion. The N22-Mn55-O53 and N31-Mn56-O54 bond angles were calculated as
76.0 and 77.1o, respectively. The N25 and N28 atoms were in the axial positions of the
Mn(III) ions and therefore the N25-Mn55-N66 and N28-Mn56-N63 bond angles were
calculated to be close to 90o. Furthermore, dihedral angles of N66-Mn55-N60-Mn56, N63-
Mn56-N60-Mn55 and Mn55-N59-Mn56-N60 were calculated as 179.6, 179.8 and 0.2o,
respectively. This result showed that the four-membered ring composed of two Mn(III) ions
and two azide nitrogen atoms was planar and that the ring atoms lay in the same plane.

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Table 2. Some selected calculated bond lengths (Å), bond and dihedral angles (o) for the (2),
(3) and (4) at the B3LYP/LanL2DZ level
(2)
(3)
Bond lengths (Å)
C1-C2
(4)
C1-C2
1.402
1.499
1.398
1.504
1.473
1.322
1.343
1.416
1.492
1.555
1.455
2.133
2.131
2.048
2.036
1.923
1.928
1.401
1.492
1.399
1.494
1.483
1.319
1.352
1.417
1.484
1.529
1.457
1.767
1.949
1.797
1.931
2.010
1.794
1.965
1.818
1.916
2.010
C1-C2
1.398
1.482
1.397
1.515
1.482
1.303
1.317
1.437
1.449
1.533
1.409
2.064
2.028
1.926
2.334
1.965
1.451
2.024
2.025
1.931
2.362
1.819
1.302
C3-C7
C3-C7
C3-C7
C11-C12
C10-C13
C13-C14
C14-N15
N15-O53
C14-N16
N16-C17
C17-C18
C20-O19
N25-Mn55
N28-Mn55
N22-Mn55
N31-Mn55
O53-Mn55
O54-Mn55
C11-C12
C11-C12
C10-C13
C10-C13
C13-C14
C13-C14
C14-N15
C14-N15
N15-O53
C14-N16
N15-O53
C14-N16
N16-C17
N16-C17
C17-C18
C17-C18
C20-O19
C20-O19
N25-Mn55
N22-Mn55
O53-Mn55
N59-Mn55
N60-Mn55
N28-Mn56
N31-Mn56
O54-Mn56
N59-Mn56
N60-Mn56
N25-Mn55
N22-Mn55
O53-Mn55
N59-Mn55
N60-Mn55
N66-Mn55
N28-Mn56
N31-Mn56
O54-Mn56
N59-Mn56
N60-Mn56
N63-Mn56
Bond angles (o)
C1-C6-C5
C1-C6-C5
C2-C3-C4
C3-C7-C8
C3-C7-C12
119.2
117.2
121.6
121.7
119.0
117.2
121.7
121.7
C1-C6-C5
C2-C3-C4
C3-C7-C8
C3-C7-C12
120.0
118.8
120.7
120.6
C2-C3-C4
C3-C7-C8
C3-C7-C12

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C9-C10-C11
C11-C10-C13
C10-C13-C14
C13-C14-N16
C14-N15-O53
C14-N16-C17
C21-C20-O19
N22-Mn55-O54
O53-Mn55-N28
117.4
121.6
118.4
123.9
124.8
121.7
109.8
89.8
C9-C10-C11
C11-C10-C13
C10-C13-C14
C13-C14-N16
C14-N15-O53
C14-N16-C17
C21-C20-O19
N22-Mn55-O53
N25-Mn55-N60
N59-Mn55-N60
N59-Mn56-N60
Mn55-N59-Mn56
N31-Mn56-O54
N28-Mn56-N60
117.8
121.5
118.7
118.1
122.6
116.9
111.7
90.9
C9-C10-C11
C11-C10-C13
117.5
122.3
120.4
124.1
123.1
122.9
109.2
76.0
C10-C13-C14
C13-C14-N16
C14-N15-O53
C14-N16-C17
C21-C20-O19
N22-Mn55-O53
N25-Mn55-N66
N59-Mn55-N60
N59-Mn56-N60
Mn55-N60-Mn56
Mn55-N59-Mn56
N31-Mn56-O54
N28-Mn56-N63
171.2
91.3
93.5
79.6
84.2
79.9
86.2
97.1
115.4
74.3
89.2
97.2
77.1
90.6
Dihedral angles (o)
C6-C1-C2-C3
C4-C3-C7-C8
0.6
C6-C1-C2-C3
C4-C3-C7-C8
0.1
C6-C1-C2-C3
C4-C3-C7-C8
0.2
-170.7
121.8
141.1
162.7
-72.5
168.1
-123.6
-128.8
-162.3
-57.6
106.1
-99.2
-5.9
-178.2
154.8
161.1
171.9
69.1
C9-C10-C13-N22
C11-C10-C13-C14
C13-C14-N16-C21
C21-C20-O19-C18
C9-C10-C13-N22
C11-C10-C13-C14
C13-C14-N16-C21
C21-C20-O19-C18
N15-O53-Mn55-N25
N46-O54-Mn56-N28
C23-N22-Mn55-N60
C30-N31-Mn56-N60
Mn55-N59-Mn56-N60
C9-C10-C13-N22
C11-C10-C13-C14
C13-C14-N16-C21
C21-C20-O19-C18
N15-O53-Mn55-N25
N46-O54-Mn56-N28
C24-N25-Mn55-N66
C29-N28-Mn56-N63
N15-O53-Mn55-N28 154.3
N25-Mn55-O54-N46 159.4
-136.8
130.8
147.2
-166.4
N22-Mn55-N31-C44
10.8
-141.6
26.4
N66-Mn55-N60-Mn56 179.6
N63-Mn56-N60-Mn55 179.8
Mn55-N59-Mn56-N60
0.2

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3.5.2. Frontier molecular orbital (FMOs) analysis
The highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular
orbitals (LUMOs) of the HBME and its metal complexes (2-4) were calculated in the gaseous
phase using B3PW91 method with 6-311G(d,p) and LanL2DZ basis sets, respectively.
HOMOs and LUMOs are known as frontier molecular orbitals (FMOs) and appear at the
outermost boundaries of electrons in the molecule. In general, HOMO expresses the ability of
the molecule to electron-donate, while LUMO relates to the ability of the molecule to accept
electrons. The energy gap between HOMO and LUMO is an important parameter for
determining the chemical stability of a molecule. Molecular orbital surfaces and energy levels
for the HOMO and LUMO of the HBME and complexes (2-4) are shown in Figs. 9-12.
Figure 9. Molecular orbital surfaces and energy levels for the HOMO and LUMO of the
HBME computed at DFT/B3PW91/6-311G(d,p) level

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Figure 10. Molecular orbital surfaces and energy levels for the HOMO and LUMO of the (2)
computed at DFT/B3PW91/LanL2DZ level

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Figure 11. Molecular orbital surfaces and energy levels for the HOMO and LUMO of the (3)
computed at DFT/B3PW91/LanL2DZ level

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Figure 12. Molecular orbital surfaces and energy levels for the HOMO and LUMO of the (4)
computed at DFT/B3PW91/LanL2DZ level
As seen from the Fig. 9, the HOMO of the HBME molecule was mainly localized on the
morpholino ring, while the LUMO was accumulated on the biphenyl moiety. This showed
that the transfer of electron density in the molecule was essentially from the morpholino ring
to the biphenyl side. On the other hand the energy gap between HOMO and LUMO provides
important information for the estimation of properties such as softness, hardness chemical
stability etc. of a molecule. The calculated energy values of HOMO and LUMO were -5.841
and -2.701 eV, respectively.

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Hard molecules have a large HOMO-LUMO gap, and soft molecules have a small HOMO-
LUMO gap. If electron transfer or rearrangement is necessary for the reaction, soft molecules
are more reactive than hard molecules [46]. HOMO-LUMO energy gap for HBME was found
to be 3.140 eV. This calculated energy gap was smaller compared to similar oxime type
compounds in the literature [47-50]. This energy gap means that the HBME molecule can be
active in chemical and biological processes.
On the other hand, the calculated HOMO-LUMO gap values were found to be 1.746, 1.630
and 1.083 eV for the complexes (2), (3) and (4), respectively. The HOMO-LUMO gaps of the
complexes (2-4) were calculated to be smaller than the HBME ligand. The smaller the
HOMO-LUMO energy gap, the more easily the electrons are excited from the ground to the
excited state, and this gap closely affects the chemical and biological activity and conductivity
of molecules. The calculated HOMO-LUMO gap values of the metal complexes were
different in the order of (4) < (3) < (2). This result means that the complex (4) has the
potential to be more active in chemical and biological areas and better semiconductor than the
complexes (2) and (3).
3.5.3. Molecular electrostatic potential (MEP) surface
The MEP surface was used to estimate the reactive behavior of the synthesized HBME
molecule. The MEP diagram provides information on how the charge distribution is in the
molecule, and also helps to predict regions for the possible nucleophilic and electrophilic
attack. The MEP surface of the HBME was calculated using B3LYP/6-311-G(d,p) level of
theory and given in Fig. 13. The red area in the diagram shows the region rich in electrons and
is more predispositions to electrophilic attack. On the other hand, the blue color zone
represents the electron-poor region and is susceptible to nucleophilic attack. The green
colored zone corresponds to the charge potential between the red and blue regions [51].