Synthesis, characterization, photoluminescence, and electrochemical studies of novel mononuclear Cu(II) and Zn(II) complexes with the 1-benzylimidazolium ligand

Article abstract of DOI:10.1016/j.molstruc.2017.03.072

Two new mononuclear coordination complexes [Cu(bim)₄Cl₂]?2H₂O (1) and [Zn(bim)₂Cl₂] (2) containing the 1-benzylimidazole (bim) ligand were successfully synthesized. Both complexes were characterized by IR, UV–vis, and fluorescence spectroscopies, single crystal and powder X-ray diffraction measurements, and thermogravimetric analysis. Self-assembly during the recrystallization process resulted in the formation of octahedral and tetrahedral Cu(II) and Zn(II) complexes, respectively. The single crystals obtained are representative of the bulk material, as shown by the powder X-ray diffraction patterns. Cyclic voltammetry measurements showed that complex 1 undergoes a quasi-reversible redox reaction, while complex 2 undergoes reduction alone, and no oxidation peak was observed; this is due to the stability of the reduced form of complex 2.

Full text of DOI:10.1016/j.molstruc.2017.03.072

Accepted Manuscript
Synthesis, characterization, photoluminescence, and electrochemical studies of novel
mononuclear Cu(II) and Zn(II) complexes with the 1-benzylimidazolium ligand
Sherino Bibi, Sharifah Mohammad, Ninie Suhana Abdul Manan, Jimmy Ahmad,
Muhammad Afzal Kamboh, Sook Mei Khor, Bohari M. Yamin, Siti Nadiah Abdul Halim
PII:
S0022-2860(17)30359-9
10.1016/j.molstruc.2017.03.072
MOLSTR 23568
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 4 January 2017
Revised Date: 17 March 2017
Accepted Date: 19 March 2017
Please cite this article as: S. Bibi, S. Mohammad, N.S.A. Manan, J. Ahmad, M.A. Kamboh, S.M. Khor,
B.M. Yamin, S.N. Abdul Halim, Synthesis, characterization, photoluminescence, and electrochemical
studies of novel mononuclear Cu(II) and Zn(II) complexes with the 1-benzylimidazolium ligand, Journal
of Molecular Structure (2017), doi: 10.1016/j.molstruc.2017.03.072.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
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Graphical abstract
Two novel coordination complexes [Cu(bim)4Cl2].2H2O (1) and [Zn(bim)2Cl2] (2) based
on benzylimidazole have been synthesized and structurally characterized. The electrochemical
behavior of the title complexes has been investigated in 4 different electrolytes.

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Synthesis, characterization, photoluminescence, and electrochemical studies of
novel mononuclear Cu(II) and Zn(II) complexes with the 1-
benzylimidazolium ligand
Bibi Sherinoa,b, Sharifah Mohammada, Ninie Suhana Abdul Manana,c, Jimmy Ahmada,
Muhammad Afzal Kambohe, Sook Mei Khora, Bohari M Yamind, and Siti Nadiah Abdul Halima*
aDepartment of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur,
Malaysia
bDepartment of Chemistry, Sardar Bahadur Khan Women University, Quetta, Balochistan, Pakistan
cCenter For Ionic Liquids (UMCiL), 50603 University Malaya Kuala Lumpur, Malaysia
dSchool of Chemical Sciences and Food Technology, University Kebangsaan Malaysia
eSchool of Chemistry, Shaheed Benazir Bhutto University Shaheed, Benazirabad, Sindh, Pakistan
Abstract
Two new mononuclear coordination complexes [Cu(bim)4Cl2] 2H2O (1) and
[Zn(bim)2Cl2] (2) containing the 1-benzylimidazole (bim) ligand were successfully synthesized.
Both complexes were characterized by IR, UV-vis, and fluorescence spectroscopies, single
crystal and powder X-ray diffraction measurements, and thermogravimetric analysis. Self-
assembly during the recrystallization process resulted in the formation of octahedral and
tetrahedral Cu(II) and Zn(II) complexes, respectively. The single crystals obtained are
representative of the bulk material, as shown by the powder X-ray diffraction patterns. Cyclic
voltammetry measurements showed that complex 1 undergoes a quasi-reversible redox reaction,
while complex 2 undergoes reduction alone, and no oxidation peak was observed; this is due to
the stability of the reduced form of complex 2.
Keywords: synthesis; Cu(II) complex; Zn(II) complex; benzylimidazole; crystal structure.
Author to whom correspondence should be addressed Dr. Siti Nadiah Abdul Halim (UM), Tel:
+603-79674248/+6019-3363554; Fax: +603-79674193; email: nadiahhalim@um.edu.my
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1. Introduction
Recently, coordination complexes have become attractive for use in the production of
medicines and drugs, primarily because most metals and organic compounds have some
biological activity, such as antifungal agents, antibiotics, and anticancer [1, 2]. However,
coordination complexes also have physical and chemical applications, such as in catalysis,
luminescence, hydrometallurgy, and sensors [3-5]. In addition, coordination complexes have
been widely used in electrochemical studies because of the different oxidation state of transition
metal [6, 7].
Coordination complexes contain ligands, which can be ions or neutral molecules, that
have lone pairs that can be donated to the central metal atom [8, 9]. The ligand can be varied by
the donor atom, for example, N, S, O, or P in phosphines [10], alkoxides, imides [11],
phosphoramidites [12], and more [13]. Benzylimidazole is a popular N-donor ligand often used
in coordination chemistry. The imidazole ring of benzylimidazole is an important component of
numerous natural products, including purine, histidine, histamine, and nucleic acids. The
exposed imidazole nitrogen atom of benzylimidazole (shown in Figure 1) can bind as a
monodentate ligand to a central metal atom [14, 15]. Benzylimidazole is also known to be good
Lewis base and metal coordinator because of its pKa value (approximately 7), and the rotational
freedom around the C-N bond in benzylimidazole (shown in Figure 1, blue color) allows
changes in molecular conformation that lead to distinct coordination compound structures [16-
18]. A large number of d-block transition metal and imidazole complexes and their derivatives
are known to have biological and physiochemical properties [19], and the coordination capability
of a number of monodentate benzylimidazole derivatives [20, 21].
Fig.1. Structure of benzylimidazole.
In this paper, we explore two novel crystal structures of benzylimidazole-based
complexes: [Cu(bim)4Cl2] 2H2O (1) and [Zn(bim)2Cl2] (2). The [Zn(bim)2Cl2] (2) complex has
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been previously reported by Pettinari and coworkers, although no crystal structure [22].
Therefore, here, we report the synthesis, spectroscopic characterization, single crystal structure,
X-ray diffraction (XRD) measurements, and thermogravimetric (TGA) analysis of complexes 1
and 2 and their electrochemical behavior. The electrochemical studies of both complexes were
carried out using cyclic voltammetry (CV).
2. Experimental
2.1. Materials and measurements
1-Benzylimidazole (Sigma–Aldrich, 99%) CuCl2.2H2O (98%; R&M chemicals), ZnCl2
(98%; R&M chemicals). Deionized water (DI) was used as the working solution. All reagents are
commercially available and were used without further purification.
The IR spectra were recorded on a Perkin-Elmer 400 FTIR Fourier transform
spectrometer (FT-FIR) between 200 and 4000 cm-1. UV-vis spectra were measured using UV-
1800 Shimadzu UV-vis spectrometer (200–800 nm), and fluorescence spectra were measured
using a JASCO FP-6500 spectrofluorometer.
Powder X-ray diffraction (PXRD) patterns were recorded on a PANalytical X'Pert Pro
diffractometer using Cu-Kα radiation (λ = 1.541874Å) in the 2θ range of 5 to 40º with a slit size
= 0.4785º. Comparison between the experimental and PXRD patterns, calculated from the
single-crystal structures, was performed using X'Pert High Score Plus.
X-ray single crystal data for complexes 1 and 2 were collected at 304(4) and 293(2) K on
a Bruker AXS SMART APEX II diffractometer with a CCD area detector (Mo Kα = 0.71073 Å,
monochromator = graphite). High-quality crystals were chosen under a polarizing microscope
and mounted on a glass fiber. Data processing and absorption correction were accomplished
using the APEXII software package [23]. The structures were solved by direct methods using
ShelXS. Hydrogen atoms were placed in geometrically constrained positions and included in the
refinement process using riding model with Uiso = 1.2Ueq C (H, H) groups. All the data were
refined with full matrix least-squares refinement against |F2| using ShelXL, and the final
refinement includes the atomic position for all the atoms, anisotropic thermal parameters for all
the non-hydrogen atoms, and isotropic thermal parameters for all the hydrogen atoms.
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Thermogravimetric analysis (SII TG/DTA 6300) was carried out using a Perkin Elmer
TGA 4000 thermogravimetric analyzer. TGA thermograms of the coordination compounds were
collected by heating the samples (which ranged from 1 to 10 mg) from 50 to 900 °C at a heating
rate of 10 °C/min under a 100-mL/min nitrogen flow. The percentage weight loss was recorded
against the temperature. Cyclic voltammograms were recorded on a CHI602E electrochemical
analyzer using a three-electrode cell.
2.2. Synthesis of [Cu(bim)4Cl2].2H2O (1)
An aqueous solution (20 mL) of CuCl2.6H2O (0.0025 M, 0.426 g) was added to a
methanol solution (20 mL) of 1-benzylimidazole (0.01 M, 1.582 g) at a molar ratio of 1:4. The
mixture was stirred for 4 to 5 h at room temperature, and then the resultant clear solution was
filtered off and allowed to stand for crystallization. Dark blue crystals formed after a week and
were analyzed by single crystal X-ray diffraction technique. Anal. Calcd for C40H44Cl2CuN8O2:
C, 59.81; H, 5.52; N, 13.95; Found: C, 58.62; H, 4.33; N, 11.26. mp = 135–148 °C. Yield = 83%.
2.3. Synthesis of [Zn(bim)2Cl2] (2)
A DMF solution (20 mL) of ZnCl2 (0.0025 M, 0.341 g) was added to a methanol solution
(20 mL) of 1-benzylimidazole (0.01 M, 1.582 g) at a molar ratio of 1:4 and the mixture was
stirred for 4 to 5 h at room temperature. Colorless crystals were obtained from the filtrate after a
week and analyzed by single crystal X-ray diffraction technique. Anal, Calcd for
C81H80Cl8N15Zn4: C, 53.03; H, 4.45; N, 12.38; Found: C, 52.55; H, 4.48; N, 11.58. The mp of
162–174 °C is in the range of previously reported proposed complex [22]. Yield = 94%.
3. Results and discussion
General and spectroscopic characterization
3.1. IR analysis
Table 1 lists the FT-IR spectral analysis of the ligand benzylimidazole and its complexes,
1 and 2. The infrared spectrum of the benzylimidazole ligand contains a prominent band at
3137 cm-1, which can be attributed to N-H stretching vibrations. The IR band appearing at
1178 cm-1 can be assigned to N-C stretching of the benzylimidazole ring [24]. As evident from
Table 1, the IR spectra of the ligand and the complexes contain peaks in a similar region.
However, some significant variations are seen in the spectra of the metal complexes and their
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free ligands. By comparing the infrared spectra of the free ligand with those of its complexes, the
coordination modes and parts of the ligand bound to the metal ion were explored. On
coordination, the stretching vibrations for the υ(N-H) and υ(C-N) bonds show a significant shift,
with υ(N-H) shifting from 3137 to 3122 and 3115 cm-1, whereas υ(C-N) shifted from 1178 to
1158 and 1150 cm-1 in metal complexes 1 and 2, respectively. New characteristic peaks, which
were absent in the spectrum of the ligand, were observed in metal complexes at 510 and
530 cm-1, indicating M-N linkages [25] for complexes 1 and 2, respectively.
<Table 1>
3.2. UV-visible absorption spectroscopy
Figure 2 shows the solid state UV-Visible spectra of the ligand and its complexes 1 and
2. As evident from the spectrum of the free ligand, a prominent absorption band appears between
200 and 300 nm with maxima at 212, 234, and 270 nm; these may be assigned to the π-π*
transitions of benzylimidazole [26, 27]. The absorption spectra of complexes 1 and 2 displayed
different absorption patterns compared to that of the free ligand. The absorption bands observed
with maxima at 335 nm in the spectrum of 1 and 211, 231, and 264 nm in the spectrum of 2 were
assigned to the π-π* transitions of the imidazole group. Complex 1 exhibited broad and sharp
absorption bands between 500 and 800 nm, which may be attributed to d-d transitions, a unique
characteristic of transition metal ions (Cu2+), whereas the spectrum of complex 2, which has a d10
metal ion (Zn2+) configuration, does not contain any peaks arising from d-d transitions [6]. The
shifting of the absorption bands in the spectra of the complexes towards higher wavelengths for
complex 1 and lower intensity for complex 2 is indicative of the metal ion coordination with the
benzylimidazole ring.
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Fig.2. Solid state UV-Visible spectra of (a) free ligand (benzylimidazole), (b) complex 1
(c) complex 2.
3.3. Fluorescence spectroscopy
Figure 3 shows the solid-state fluorescence emission spectra of the free ligand and its
complexes, 1 and 2, at ambient temperature. As obvious from the figure, the emission spectrum
of the free ligand contains three significant emission peaks at λmax = 308, 367, and 420 nm upon
excitation at 270 nm, and these may be assigned to the π-π* transitions of the delocalized π
electrons in the imidazole ring and the n-π* transitions of the n-electrons of the nitrogen atoms of
imidazole [28]. The emission spectrum of complex 1 contains two emission peaks at 375 and 497
nm upon excitation at 335 nm, whereas complex 2 displayed two emission peaks at 297 and 419
nm upon excitation at 264 nm. Comparing the emission spectral data of the free benzylimidazole
ligand with those of its complexes, the emergence of new peaks in the emission spectra of the
complexes can be attributed to the π-π* transition of the benzylimidazole ligands with metal ion
charge transitions. In addition, there is fluorescence quenching in complexes 1 and 2. The
fluorescence quenching of a ligand by transition metal ions during complexation is a common
phenomenon and can be explained by processes such as magnetic perturbation, redox activity,
and electronic energy transfer [29-31]. On the formation of metal complexes, the energy of the
ligand excited states, which are responsible for the emission spectrum, transfers to the metal
ions, leading to a decrease in the fluorescence intensity [32].
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Fig. 3. Fluorescence spectra for (a) free ligand (benzylimidazole) (b) complex 1 (c)
Complex 2.
3.4. Crystal structure description
Complex 1 crystallized in the monoclinic space group P21/c. The crystal data and structural
refinement parameters are shown in Table 2.
Complex 1 possesses one half-molecule with the center of symmetry at the Cu1 atom in the
asymmetric unit, and the molecular structure is shown in Figure 4a. However, the octahedral
geometry is due to the long-range interactions of Cu1 with the two Cl atoms occupying the axial
positions. The Cu-Cl1 distances are 3.0897(7) Ǻ. Similar observations has been observed in
catena-poly[bis(1-methyl-1-tetrazole-ĸN4)copper(II)]-di-ꢀ-bromo], in which the Cu-Br bond
length is 3.101(4) Å [33]. The N2, N2A, N3, and N3A nitrogen atom of the imidazole rings
occupy equatorial positions, with N2–Cu1–N3 and N2–Cu1–N3 bond angles of 86.94(7) and
93.06(7)°, respectively, making the geometry slightly distorted. The Cu1–N2 and Cu1-N3 bond
lengths of 1.9887(17) and 2.0253(16) Å, respectively, are longer than that in [Cu(bhs)(Hdmpz)]
(1.924(2) Å) [34]. Other bond length and angles are normal and comparable to the Zn complex
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(Table 3). The cis imidazole rings, N1/N2/C8-C10 and N3/N4/ (C11-C13), are not coplanar but
are twisted with an angle of 45.98°.
Fig. 4a. Molecular structure of complex 1.
In the crystal packing structure of complex 1, the interactions are dominated by C11-
H11 Cl1 and intermolecular hydrogen bonds between the water molecules and chloride atoms,
forming a two-dimensional network (Figure 4b). All the symmetry codes are given in Table 4.
Fig. 4b. Crystal packing of complex 1 viewed down a axis. The dashed lines indicate hydrogen
bond except chlorine to Cu atoms.
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Complex 2 crystallized in the triclinic space group P-1. The asymmetric unit contains four
crystallographic independent complexes. In the molecular structure of complex 2, the Zn atom is
coordinated by two nitrogen atoms (from two benzylimidazole ligands) and two chlorides,
resulting in a tetrahedral coordination geometry (Figure 5a).
Fig. 5a. Asymmetric unit of complex 2.
The two chloride atoms located at the basal position have Cl1-Zn1-Cl2, Cl3-Zn2-Cl4, Cl5-
Zn3-Cl6, and Cl7-Zn4-Cl8 bond angles ranging from 117.45(2) to 119.87 (2)°, while the two
nitrogen atoms of the imidazole rings are in equatorial positions with N1-Zn1-N3, N7-Zn2-N5,
N9-Zn3-N11, and N13-Zn4-N15 bond angles of 108.02(7) to 108.52(7)°, resulting in a
significantly distorted tetrahedral geometry. The cis benzylimidazole rings are not coplanar. The
Zn-N bond lengths (Zn1-N1, Zn1-N3, Zn2-N7, Zn2-N5, Zn3-N9, Zn3-N11, Zn4-N13, and Zn4-
N15) range from 2.0022(17) to 2.0106(17) Å, and these are slightly shorter than those in
[ZnCl2(C14H12N2)2], which have bond lengths ranging from 2.0048(17) to 2.0225(17) Å to the
imidazole group [35, 36]. Other bond lengths and angles are within normal ranges (Table 3).
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As shown in the crystal packing diagram, the intermolecular interactions are dominated
by C-H Cl and C-H π interactions (blue dotted line), resulting in three-dimensional layers
(Figure 5b). There are no classical hydrogen bonds in the structure.
Fig. 5b. Crystal packing of complex 2 viewed down a axis.
<Table 2>
<Table 3>
<Table 4>
3.5. X-ray powder diffraction pattern
Figure 6 shows the experimental powder X-ray diffraction patterns for the Cu(II) and Zn(II)
coordination complexes, which agree well with the simulated patterns calculated from the single crystal
structures of complexes 1 and 2, indicating that the samples are single phase and free from impurities.
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Fig.6. X-ray powder diffraction pattern of complex 1 and complex 2 (Black- simulated from
CIFs, Red and Blue Experimental).
3.6. Thermogravimetric analysis
The results of TGA analysis for complex 1 and 2 are given in Table 5. The TGA and
derivative thermal gravitational analysis (DTG) profiles (Figure 7) of complex 1 show a three-
step degradation process with rapid weight losses of 3.6, 54.9, and 13.5% at 49.85–102.50,
135.41–298.85, and 486.43–731.05 °C, respectively, corresponding to the loss of the ligands,
leaving 29% as the final residue. Based on the experimental method, the 29% residue is proposed
to be Cu3N3, which has a calculated percentage weight of 27.1%. The decomposition of complex
2 starts at 148.92–604.74 °C with an 88.1% weight loss, corresponding to the removal of all
ligands. The calculated value of the end residue matched well with the proposed metallic zinc
residue. Because of its high initial decomposition temperatures (greater than 148 °C), complex 2
is more thermally stable than complex 1.
<Table 5>
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Fig.7. TGA Curve of (a) complex 1 (b) complex 2.
3.7. Electrochemical study
Electrochemical studies were performed for complexes 1 and 2. Due to the different
metal oxidation states, some redox properties are expected. Electrochemical measurements were
carried out using a glassy carbon electrode in the presence of four different electrolytes: KCl,
phosphate buffer, TRIS, and ammonium chloride (Table 6) at a scan rate of 50 mVs-1. As shown
in Figure 8, the peak potential separations (Epc − Epa) for complex 1 were 107, 93, 122, and
102 mV in KCl, phosphate buffer, TRIS, and NH4Cl electrolyte solutions, respectively, and the
ratios of cathodic current to anodic current Ipc/Ipa are 0.9, 0.86, 0.81, and 0.87, respectively,
indicating that the redox reaction of the complex was quasi-reversible. Only one redox couple
was detected for complex 1 using the previously mentioned conditions, which suggests that the
cathodic peak is due to the reduction of Cu(II) to Cu(I). When the potential scan was reversed to
positive potentials, anodic waves were observed at 0.01, 0.13, 0.12, and 0.15 V, respectively,
indicating the oxidation of Cu(I) to Cu(II) [37]. In contrast, under the same condition, only one
reduction peak was observed for complex 2, which indicates that Zn(II) was reduced to Zn(0) at -
0.68 V. The absence of an anodic peak in the reverse scan suggests that the reduced form of
complex 2 is more redox stable.
<Table 6>
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Figure 8: Cyclic voltammogram at a scan rate of 50 mVs-1for (a) complex 1 (b) complex
2 using glassy carbon electrode (diameter = 2mm) in the presence 50mM KCl , phosphate
buffer,TRIS,and ammonium chloride electrolyte solution.Scanning was performed against
Ag/AgCl (sat.KCl) reference electrode.
4. Conclusions
We have successfully synthesized and structurally characterized two new coordination
complexes [Cu(bim)4Cl2] 2H2O (1) and [Zn(bim)2Cl2] (2). Spectroscopic techniques confirmed
the metal-ligand coordination, and single X-ray diffraction results show that Cu(II) complex is
octahedral geometry, while the Zn(II) complex is tetrahedral. Both complexes exhibit
photoluminescence properties. In the electrochemical measurements, the voltammogram of
complex 1 shows quasi-reversible redox reaction, while complex 2 shows only one reduction
peak and no oxidation peak, arising from its stability in reduced form.
Supplementary material
CCDC No. 1478266 and 1519004 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cambridge Crystallographic Data
Center via http://www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgements
Financial support from University Malaya of Research Grant (RP011B-14SUS), IPPP
(PG116-2014B), High Impact Research Grants (UM-MOHE
grant
UM.C/625/1/HIR/MOHE/SC/09), Fundamental Research Grant Scheme, FRGS (FP005-2015A),
UKM-Dip 2014-16 Research Grant and Higher Education Commission of Pakistan under FDP
are acknowledged.
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Table 1. IR spectral data of ligand benzylimodazole and its complexes 1 and 2.
Compound
Ligand
υ(N-H)
3137
υ(C-N)
1178
υ(M-N)
-
(benzylimidazole)
Complex 1
Complex 2
3126
3115
1158
1104
510
530
Table 2. Crystal data and structure parameters for crystal complex 1 and complex 2.
1
2
CCDC No
Empirical formula
Formula weight
1478266
C40H44Cl2CuN8O2
803.27
1519004
C81H80Cl8N15Zn4
1808.68
293(2)
triclinic
P-1
Temperature/K
Crystal system
Space group
a/Å
304(2) K
monoclinic
P21/c
10.9435(7)
12.3756(4)
b/Å
c/Å
17.8491(13)
10.5662(6)
90
109.201(2)
90
14.5480(4)
24.7577(7)
106.590(2)
104.191(3)
90.275(3)
α /˚
β/˚
γ /˚
Volume/ Å3
1949.1(2)
4128.1(2)
2
1.455
4.119
1854.0
0.3 × 0.3 × 0.3
7.4 to 149.4°
28752
Z
2
Density (calculated) /g/m3
1.369
0.743
Absorption coefficient/ mm-1
F(000)
838.0
Crystal size/ mm3
0.430 × 0.240 × 0.160
3.0 to 28.3°.
63639
Theta range for data collection
Reflections collected
Independent reflections
Completeness to theta = 28.3°
Max. and min. transmission
Refinement method
4845 [R(int) = 0.0587]
99 %
16214 [R(int) = 0.0262]
99 %
0.088 and 1.000
0.8903 and 0.7405
Full-matrix least-squares on F2 Full-matrix least-squares on F2
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices
1.062
1.005
R1 = 0.0448, wR2 = 0.0927
R1 = 0.0775, wR2 = 0.1067
0.23 and -0.88
R1 = 0.0409, wR2 = 0.1141
R1 = 0.0470, wR2 = 0.122
0.77 and -0.78
Largest diff. peak and hole/ e.Å-3
1

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Table 3. Selected bond lengths (Å) and bond angles (°) for complex 1 and 2.
Complex 1
Atom
Cu1–N2
Cu1-N3
Cu1-Cl1
N(3)-C(1)
Length/Å
1.9887(17)
2.0253 (16)
3.0897(7)
1.310
Atom
H(1WA)-O(1W)-H(1WB)
N(2A)-Cu(1)-N(2)
N2–Cu1–N3
Angle / °
107(4)
180.0
86.94(7)
93.03(7)
N2–Cu1–N3A
Complex 2
Atom
Length/Å
2.0096(17)
2.0106(17)
2.2511(6)
2.2572(5)
2.0060(16)
2.0087(17)
2.2500(5)
2.2535(5)
2.0079(17)
2.0111(17)
2.2507(5)
2.2531(5)
2.0022(17)
2.0160(17)
2.2526(5)
2.2495(5)
Atom
Angle/ °
108.35(7)
108.52(7)
108.20(7)
108.02(7)
117.45(2)
118.24(2)
119.87(2)
117.85(2)
102.3(5)
112.30(5)
102.41(5)
111.35(5)
104.01(5)
113.30(5)
111.97(5)
111.52(5)
Zn(1)-N(1)
Zn(1)-N(3)
Zn(1)-Cl(1)
Zn(1)-Cl(2)
Zn(2)-N(7)
Zn(2)-N(5)
Zn(2)-Cl(4)
Zn(2)-Cl(3)
Zn(3)-N(9)
Zn(3)-N(11)
Zn(3)-Cl(5)
Zn(3)-Cl(6)
Zn(4)-N(13)
Zn(4)-N(15)
Zn(4)-Cl(7)
Zn(4)-Cl(8)
N(1)-Zn(1)-N(3)
N(7)-Zn(2)-N(5)
N(9)-Zn(3)-N(11)
N(13)-Zn(4)-N(15)
Cl(1)-Zn(1)-Cl(2)
Cl(4)-Zn(2)-Cl(3)
Cl(5)-Zn(3)-Cl(6)
Cl(8)-Zn(4)-Cl(7)
N(15)-Zn(4)-Cl(7)
N(1)-Zn(1)-Cl(1)
N(7)-Zn(2)-Cl(4)
N(9)-Zn(3)-Cl(5)
N(13)-Zn(4)-Cl(8)
N(3)-Zn(1)-Cl(2)
N(5)-Zn(2)-Cl(4)
N(11)-Zn(3)-Cl(6)
Table 4. Hydrogen Bond (Å) for complex 1.
Complex 1
d(H…..A)
D-H……A
d(D-H)
0.82(2)
0.82(4)
0.93
d(D…A)
d(D-H…..A)
158(3)
2O(1W)-H(1WA)…Cl1
2O(1W)-H(1WB)….Cl1
C(11)-H(11)…….Cl1
x,1/2-y,1/2+z
2.52(2)
2.65(4)
2.77
3.293(3)
3.424(3)
3.462(2)
158(4)
132
2

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Table 5. TGA analysis for complex 1 and complex 2.
complex
Decomposition Range
Temperature range Weight loss
(°C) (%)
Remaining
Weight
Expected
Resides
(%)
Exp., (Calc.)
49.85 °C - 102.50 °C
135.41 °C - 298.85 °C
486.43 °C – 731.05 °C
3.6
54.9
13.5
29 (27.1)
Cu3N2
1
2
148.92 °C - 290.48 °C
291.39 °C - 400.83 °C
423.87 °C - 604.74 °C
43.3
35.4
9.4
10.9 (14.3)
metallic zinc
Table 6. Electrochemical study Complex 1 and Complex 2 in different electrolytes solutions
using glassy carbon electrode.
Complex 1
Glassy carbon
Electrolytes
EP,A
EP,C
E1/2
Phosphate buffer
TRIS
0.00977
0.13184
0.12451
0.15137
0.10254
0.00977
0.01709
0.04883
0.05615
0.07080
0.13794
0.10010
KCl
NH4Cl
Complex 2
Glassy carbon
Electrolytes
Phosphate buffer
TRIS
EP,A
No
No
No
No
EP,C
0.67871
0.68359
0.67627
0.68359
E1/2
No
No
No
No
KCl
NH4Cl
3

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RESEARCH HIGHLIGHTS
•
•
Synthesis of two new Cu (II) and Zn (II) coordination complexes with 1-benzylimidazole (bim)
ligand; [Cu(bim)4Cl2].2H2O (1) and [Zn(bim)2Cl2] (2).
Characterization of the complexes by FT-IR, UV-Vis and fluorescence spectroscopic
techniques, Powder and Single Crystal X-ray Diffraction Analysis and
Thermogravimetric analysis.
•
The complexes show redox properties due to different oxidation state of transition metal
(Cu2+, Zn2+).