Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol: Synthesis, characterization, crystal structures and anti-tuberculosis assay with docking studies

Article abstract of DOI:10.1016/j.poly.2017.02.010

Transition metal coordination complexes of Co(II), Ni(II), Cu(II) and Zn(II) with a newly designed ligand, 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol have been synthesized and characterized using various spectro-analytical techniques. The molecular structures of Co(II), Cu(II) and Zn(II) complexes are determined by single-crystal X-ray diffraction method. The metal to ligand stoichiometry has been found to be 1:2 in the case of Cobalt(II), Nickel(II) and Zinc(II) whereas 1:1 in the case of Copper(II) complex. The newly synthesized ligand and complexes have been assessed for their growth inhibiting potencies against H37Rv strain of Mycobacterium tuberculosis. The copper and cobalt complexes have emerged to be potent in vitro growth inhibitors of H37Rv. All the complexes are inhibiting the growth of other tested common microbial flora to a significantly lesser extent, making them selective towards H37Rv in the preliminary analysis. The consensus scores obtained by the docking studies of the molecules to the target protein enoyl acyl carrier protein reductase of M. tuberculosis H37Rv are in good agreement with the obtained MIC values.

Full text of DOI:10.1016/j.poly.2017.02.010

Accepted Manuscript
Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazo-
no)propan-1-ol: Synthesis, Characterization, Crystal structures and anti-tuber-
culosis assay with docking studies
Vinayak Kamat, Dhoolesh Kokare, Krishna Naik, Avinash Kotian, S. Naveen,
Sheshagiri R. Dixit, N.K. Lokanath, Shrinivas D Joshi, Vidyanand K. Revankar
PII:
S0277-5387(17)30120-1
DOI:
http://dx.doi.org/10.1016/j.poly.2017.02.010
POLY 12477
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
19 December 2016
8 February 2017
9 February 2017
Please cite this article as: V. Kamat, D. Kokare, K. Naik, A. Kotian, S. Naveen, S.R. Dixit, N.K. Lokanath, S.D.
Joshi, V.K. Revankar, Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol:
Synthesis, Characterization, Crystal structures and anti-tuberculosis assay with docking studies, Polyhedron (2017),
doi: http://dx.doi.org/10.1016/j.poly.2017.02.010
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Transition metal complexes of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol :
Synthesis, Characterization, Crystal structures and anti-tuberculosis assay with docking studies
Vinayak Kamata, Dhoolesh Kokarea, Krishna Naika, Avinash Kotiana, Naveen S.b, Sheshagiri R.
Dixitc, Lokanath N.K.d, Shrinivas D Joshic and Vidyanand K. Revankara*
a Department of Chemistry, Karnatak University, Dharwad-580003, India.
b Institution of Excellence, Vijnana Bhavan, University of Mysore, Manasagangotri, Mysuru-
570 006, India.
c
Novel Drug Design and Discovery Laboratory, Department of Pharmaceutical Chemistry,
S.E.T.’s College of Pharmacy, Sangolli Rayanna Nagar, Dharwad-580 002, Karnataka, India.
d Department of Studies in Physics, University of Mysore, Manasagangotri, Mysuru-570 006,
India.
* Corresponding author
Abstract : Transition metal coordination complexes of Co(II), Ni(II), Cu(II) and Zn(II) with a newly
designed ligand, 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol have been synthesized and
characterized using various spectro-analytical techniques. The molecular structures of Co(II), Cu(II)
and Zn(II) complexes are determined by single-crystal X-ray diffraction method. The metal to ligand
stoichiometry has been found to be 1:2 in the case of Cobalt(II), Nickel(II) and Zinc(II) whereas 1:1
in the case of Copper(II) complex. The newly synthesized ligand and complexes have been assessed
for their growth inhibiting potencies against H37Rv strain of Mycobacterium tuberculosis. The copper
and cobalt complexes have emerged to be potent in vitro growth inhibitors of H37Rv. All the
complexes are inhibiting the growth of other tested common microbial flora to a significantly lesser
extent, making them selective towards H37Rv in the preliminary analysis. The Consensus scores
obtained by the docking studies of the molecules to the target protein enoyl acyl carrier protein
reductase of M. tuberculosis H37Rv are in good agreement with the obtained MIC values.
Key Words : 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol, 2-hydrazinobenzimidazole,
transition metal complexes, antituberculosis against H37Rv, enoyl acyl carrier protein reductase of M.
tuberculosis H37Rv, docking of metal complexes.

Highlights :




A
novel benzimidazole based tridentate ligand 2-(2-(1H-benzo[d]imidazol-2-
yl)hydrazono)propan-1-ol is synthesized and characterized.
Co(II), Ni(II), Cu(II) and Zn(II) metal complexes of the ligand are synthesized and
characterized by the single crystal X-ray diffraction method.
Ligand and complexes are tested for their antibacterial (including antitubercular) and
antifungal potencies.
The observed in-vitro results are supported by docking studies on target protein enoyl acyl
carrier protein reductase of M. tuberculosis H37Rv.
1. Introduction
Transition metal complexes of hydrazone based Schiff base ligands are of particular
interest in the field of coordination chemistry. Hence these have been reported in the literature
for a long time [1]. In recent years, Schiff bases with nitrogen and oxygen donors have drawn
special attention due to their structural lability, ability to possess unusual configurations, and
their sensitivity to molecular environments [2, 3].
Ever since the discovery of cisplatin, years have witnessed the progress in biological
applications of transition metal coordination complexes [4]. Manipulation of the properties of
biopotent ligands by complexation has continued to be an active field for clinical therapeutic
applications [5]. Versatility in oxidation states, ease of complexation, a variety of electronic
properties, ligand-induced tunability of geometry and coordination numbers makes transition
metals suitable for this purpose over the main group elements [6]. Transition metal complexes
of vanadium as antidiabetic agents [7-9], copper complexes as plausible anticancer agents[10],
cobalt and copper complexes as antimicrobial/antitubercular agents are few of well-established
examples [11, 12].
H37Rv is the most virulent and most studied strain of TB in research laboratories. Recently,
substituted benzimidazole derivatives have emerged to be the promising class for the growth
inhibition of H37Rv [13-15]. Moreover, these organic moieties have undergone excellent activity
enhancement upon metallation [16, 17]. Literature even reveals significant successes of copper
complexes as anti-TB agents, especially with potential tridentate chelators [18, 19]. Considering these
facts, herein we report the synthesis, characterization and crystal structures of novel transition metal
complexes of a designed tridentate N,N,O-chelator.

2. Experimental
2.1. General
Hydroxyacetone obtained from Sigma-Aldrich and other reagents obtained from
Spectrochem were used as supplied. Solvents were purified and dried according to standard
procedures. The metal salts used were in their hydrated form, i.e., CoCl2.6H2O, NiCl2.6H2O,
1
13
CuCl2.2H2O and Zn(NO3)2.6H2O. The H and C NMR spectra were recorded on AGILENT
VNMRS-400 spectrometer, in DMSO-d6 solvent. Infrared spectra of the ligand and its metal
complexes were recorded in KBr discs in the region 4000–400 cm−1 on a Nicolet-6700 FT-IR
spectrometer. The CHN analysis was carried out using a Thermo quest elemental analyzer.
The solution state UV–Vis spectra of all the compounds in DMF were recorded on a JASCO
V-670 50 UV-Vis spectrophotometer. Thermal behavior of the metal complexes was analyzed
on a Universal V2.4F TA instrument, from room temperature to a final temperature of
1000 °C at the heating rate of 10 °C/min. The cyclic voltammetric experiments were carried
out with a three electrode apparatus using a CHI630D electrochemical analyzer (USA). The EI
mass spectrum of the ligand was obtained with a Shimadzu GCMS-QP2010S spectrometer.
The ESI mass spectral data for all the complexes were obtained using a Waters UPLCTQD
mass spectrometer. The molar conductivity measurements of 1mM complex solutions in DMF
were carried out on equiptronics EQ-665 conductivity bridge.
2.2. Single crystal X-ray crystallography
Single crystals of suitable dimensions were chosen carefully for X-ray diffraction
studies. The X-ray intensity data were collected on a Bruker Proteum2 CCD diffractometer
equipped with an X-ray generator operating at 45 kV and 10 mA, using Cu-Kα radiation of
wavelength 1.54178 Å or on a Bruker APEX2 CCD area-detector diffractometer using
graphite monochromated Mo-Kα radiation of wavelength 0.71073 Å. The Data were collected
for 24 frames per set with different settings of φ (0° and 90°), keeping the scan width of 0.5°,
exposure time of 2 s, the sample to detector distance of 45.10 mm and 2θ value at 46.6°. The
complete data sets were processed using SAINT PLUS [20]. The structures were solved by
direct methods and refined by a full-matrix least squares method on F2 using SHELXS and
SHELXL programs [21]. The geometrical calculations were carried out using the program
PLATON [22]. The molecular and packing diagrams were generated using the software
MERCURY-3.8 [23]. A summary of the crystallographic data is tabulated in table 1.
Table 1. Crystal data and structure refinement for the complexes [CoL2]Cl2, [CuLCl2] and [ZnL2](NO3)2
Identification code
Empirical formula C20H27Cl2CoN8O2
[CoL2]Cl2
[CuLCl2]
C10H12Cl2CuN4O
338.68
[ZnL2](NO3)2
C22H30N10O9 Zn
643.93
Formula weight
Wavelength
538.30
0.71073 Å
1.54178 Å
1.54178 Å

Crystal system
Space group
Unit cell
dimensions
a
b
c
a
b
Monoclinic
P21/n
Monoclinic
C2/c
Triclinic
P-1
8.3006(3) Å
9.5927(4) Å
30.7015(12) Å
90°
95.284(2)°
90°
10.9099(3) Å
11.4342(3) Å
20.3605(6) Å
90°
93.1690(10)°
90°
8.1759(6) Å
9.1983(6) Å
18.7444(13) Å
96.095(2)°
90.131(2)°.
101.235(2)°
1374.45(17) Å3
2
g
Volume
Z
2434.22(16) Å3
4
2536.01(12) Å3
8
Density
1.469 Mg/m3
1.774 Mg/m3
1.556 Mg/m3
(calculated)
Absorption
coefficient
F(000)
0.958 mm-1
6.263 mm-1
1.856 mm-1
1108
1368
668
Theta range for
data collection
Reflections
collected
Independent
reflections
Completeness to
theta
1.33 to 25.60°.
4.35 to 64.20°.
4.75 to 64.87°.
16173
10983
17792
4551 [R(int) = 0.0857]
99.2%
2079 [R(int) = 0.0391]
98.10%
4556 [R(int) = 0.0368]
97.90%
Max. and min.
transmission
Refinement
method
Data / restraints /
parameters
0.9102 and 0.7004
0.3530 and 0.3035
0.6541 and 0.6060
Full-matrix least-squares
on F2
4551 / 0 / 298
Full-matrix least-squares on Full-matrix least-
F2
2079 / 0 / 175
squares on F2
4556 / 0 / 428
Goodness-of-fit on 1.057
1.059
1.039
F2
Final R indices
[I>2sigma(I)]
R indices (all data) R1 = 0.0717, wR2 =
0.1493
R1 = 0.0504, wR2 =
0.1390
R1 = 0.0316, wR2 = 0.0823 R1 = 0.0403, wR2 =
0.1064
R1 = 0.0324, wR2 = 0.0831 R1 = 0.0414, wR2 =
0.1075
2.3. Synthesis of 2-(2-(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol (L)
The schematic representation of the synthesis of ligand is given in scheme 1. First, 2-
bromobenzimidazole was obtained from 2-mercaptobenzimidazole by the reported method
[24]. In the next step, 2-bromobenzimidazole (1.97 g, 10 mmol) was refluxed in 20.0 mL of
80% hydrazine hydrate solution, to obtain 2-hydrazinobenzimidazole (1.35 g, Yield : 91%)
[25]. Finally, to the magnetically stirred methanolic solution of 2-hydrazinobenzimidazole
(1.65 g, 10.0 mmol), hydroxyacetone (0.740 g, 10.0 mmol) in methanol was added dropwise.
The mixture was refluxed on a water bath for 1 h. The progress of the reaction was monitored

by TLC. The buff colored precipitate formed was filtered and washed with cold methanol. The
solid product was dried in vacuo for 4 h.
Yield 52%; m.p. 210°C; Color: buff. Anal. Calc. for C10H12N4O (%) : C, 58.81; H, 5.92; N,
27.43; O, 7.83. Found for L (%) : 58.3; H, 6.2; N, 27.8; O, 7.7. FTIR (in cm−1): ν(C=N) 1637;
benzimidazole ring, ν(C=N) 1578; hydrazine, ν(NH) 3246 and 3111; ν(O-H) 3440; ν(C–O)
1029. 1H NMR (400 MHz, DMSO-d6) δ: 11.36 (s, 1H, N2H), 10.22 (s, 1H, N3H), 7.17 (d, 2H,
J = 8Hz, C6H and C9H), 6.99 (s, 2H, C7H and C8H), 4.88 (t, 1H, J = 5.6Hz, OH), 4.04 (d, 2H, J
13
= 5.6Hz, C1H2), 1.88 (s, 3H, C3H3). C NMR (100 MHz, DMSO-d6) δ: 154.92 (C2), 150.76
(C4), 142.68, 133.54, 120.68, 119.34, 115.28, 109.67 (C5-C10, Ph), 65.62 (C1), 13.86 (C3).
EI-MS (m/z): 204 ([M]+).
H
N
H
N
Br2, HBr
SH
Br
C
N
N
CH3COOH, RT, Stir 4 h
Yield : 80%
MP : 190-192 0
Reflux 4 h
NH2-NH2.H2O (80%)
3
3
H
N
2
H
2
N
4
H
N
5
6
N
1
1
CH3COCH2OH
HN
H2N
7
N
OH
4
10
N
Methanol, Reflux 1h
9
8
Yield : 91%
MP : 224-2250C
L
Yield : 52%
MP : 2100C
Scheme 1 Synthesis of ligand
2.4. Syntheses of metal complexes
Schematic representation of the synthesis of the complexes is given in scheme 2.
Co(II) and Ni(II) complexes were obtained by refluxing the respective hexa hydrated metal
chlorides (0.119 g, 0.500 mmol) with the methanolic solution of ligand (0.204 g, 1.00 mmol)
for 4 h. The crystalline product was obtained by evaporating the solvent under reduced
pressure. Single crystals were obtained by evaporating the methanolic solution of respective
complexes. To the methanolic solution of ligand (0.204 g, 1.00 mmol), a methanolic solution
of CuCl2.2H2O (0.171 g, 1.00 mmol) was added dropwise and the resulting suspension was
stirred for 1 h at room temperature. The brown precipitate obtained was filtered off, washed
with cold methanol and dried in vacuo. Tiny single crystals suitable for X-ray diffraction were
obtained by slow evaporation of the filtrate. Whereas the Zn(II) complex was obtained by
refluxing Zn(NO3)2.6H2O (0.149 g, 0.500 mmol) with the methanolic solution of ligand
(0.204 g, 1.00 mmol) for 4 h. The white product was filtered and washed with methanol.
Single crystals were obtained by evaporating the ethanolic solution of the complex.

H
H
H
N
H
N
N
N
N
N
HO
HO
N
N
Ni
Co
2Cl-
N
2Cl-. 2H2O.CH3OH
N
OH
OH
N
N
H
N
N
H
N
N
H
H
CoCl2.6H2O
NiCl2.6H2O
Methanol
Reflux, 4 h
Methanol
[NiL2]Cl2
Reflux, 4 h
H
[CoL2]Cl2
H
N
N
N
2
HO
N
Zn(NO3)2.6H2O
Methanol
Reflux, 4 h
2 CuCl2.H2O
H
N
H
N
Methanol
RT, Stir
1 h.
N
HO
H
N
N
H
N
N
Zn
HO
2(NO3)-.C2H5OH
N
N
OH
Cu
Cl
Cl
N
N
N
H
H
[ZnL2](NO2)2
[CuLCl2]
Scheme 2 Synthesis of complexes
2.4.1. [CoL2]Cl2
Color: Faint pink, Yield: 55%. Anal. Calc. for C20H24Cl2CoN8O2: C, 44.62; H, 4.49; Cl, 13.17;
Co, 10.95; N, 20.82; O, 5.94. Found: C, 44.2; H, 4.6; Cl, 12.9; Co, 11; N, 21.7; O, 6.2. λmax
(nm) εM (L M-1 cm-1): 466 (130), 798 (16), 921 (10) (d–d transitions). IR (cm−1): ν(NH) 3150;
ν(C=N) 1584, ν(O-H) 3440 ; ν(C–O) 1060. ESI-MS (positive mode m/z) 466 ([CoL2-H]+),
233.5 ([CoL2]2+) Molar conductivity (Ohm-1 cm2 mol-1): 210.
.
2.4.2. [NiL2]Cl2
Color: Blue, Yield: 62%. Anal. Calc. for C21H32Cl2N8NiO5 : C, 41.61; H, 5.32; Cl, 11.70; N,
18.49; Ni, 9.68; O, 13.20. Found: C, 41.1; H, 5.5; Cl, 12.1; N, 18.6; Ni, 9.9; O, 12.8. λmax (nm)
εM (L M-1 cm-1): 453 (44), 601(14), 924 (25) (d–d transitions). IR (cm−1): ν(NH) 3160; ν(C=N)
1584, ν(O–H) 3440 ; ν(C–O) 1053. ESI-MS (positive mode m/z) 465 ([NiL2-H]+), 233
([NiL2]2+). Molar conductivity (Ohm-1 cm2 mol-1): 225.
2.4.3. [CuLCl2]
Color: Brown, Yield: 43%. Anal. Calc. for C10H12Cl2CuN4O: C, 35.46; H, 3.57; Cl, 20.94; Cu,
18.76; N, 16.54; O, 4.72. Found: C, 35.6; H, 3.3; Cl, 21; Cu, 18.2; N, 16.7; O, 5.2. λmax (nm)
εM (L M-1 cm-1) : 757 (72) (d–d transition). IR (cm−1): ν(NH) 3164 ; ν(C=N) 1612, ν(O–H)
3440 ; ν(C–O) 1047. ESI-MS (positive mode m/z) 266 ([CuL-2Cl-H]+). Molar conductivity
(Ohm-1 cm2 mol-1): 35.

2.4.4. [ZnL2](NO3)2
Color: White, Yield: 65%. Anal. Calc. for C22H30N10O9Zn: C, 41.04; H, 4.70; N, 21.75; O,
22.36; Zn, 10.15. Found: C, 40.5; H, 5.1; N, 21.3; O, 22.95; Zn, 10.15. IR (cm−1): ν(NH) 3207;
ν(C=N) 1633, ν(O–H) 3440 ; ν(C–O) 1070; ν (N–O) 1384. ESI-MS (positive mode m/z) 472
([M-2(NO3)]+). 1H NMR (DMSO-d6) δ: 12 (b, 4H, N2H and N3H ), 7.33-7.02 ( b, C6-C9H, 8H),
4.31 (s, 4H, C1H2), 3.40 (q, 2H, J = 6.8 Hz, ethanol), 3.13 (s, 2H, OH), 2.16 (s, 6H, C3H3),
1.02 (t, 3H, J = 6.8 Hz, ethanol). 472 ([ZnL2-H]). Molar conductivity (Ohm-1 cm2 mol-1): 240.
2.5. Growth inhibitory activity of H37 RV using MABA[26]
The in vitro growth inhibitory activity of compounds were assessed against M. TB
H37Rv genome using microplate Alamar Blue assay (MABA). MABA is sensitive, rapid,
inexpensive, nonradiometric, non-toxic and offers the potential for screening, with or without
analytical instrumentation for a large number of antimicrobial compounds against slow-
growing mycobacteria such as H37Rv, H37Ra, and M. avium [27]. Overall, MICs determined
either visually or fluorometrically in MABA were highly correlated with those determined in
the BACTEC 460 system. Briefly, 200 μL of sterile deionized water was added to all outer
perimeter wells of sterile 96 wells plate to minimize the evaporation of medium in the test
wells during incubation. The 96 wells plate was loaded with 100 μL of the Middlebrook 7H9
broth. Serial dilution of compounds was made directly on the plate. The final drug
concentrations tested were 100 to 0.2 μg/mL. Parafilm-covered sealed plates were covered and
incubated at 37 °C for five days. Since H37Rv is categorized as a slow growing bacteria, five
days long incubation period is necessary to overcome the imposed limitation in MABA. After
the incubation period, 25 μL of freshly prepared 1:1 mixture of Almar Blue reagent and 10%
tween 80 was added to the plate. Again the plate was incubated for 24 h. A blue color in the
well was scored as no bacterial growth, and pink color was interpreted as growth. The MIC
was defined as lowest drug concentration which prevented the color change from blue to pink.
2.6. Growth inhibitory activity of other microbial strains[28]
The MIC values of all synthesized compounds for the growth inhibition of four
different microbial genomes S. aureus, E.coli, A.niger and C.albicans were determined in
HIMEDIA M210 Brain heart infusion broth (BHI). Brain Heart Infusion broth, which is used
for the propagation of pathogenic cocci and other fastidious organisms associated with allied
pathological investigations had the following composition.
Ingredients in g/L. Calf brain, infusion from, 200.00; Beef heart infusion from, 250.00;
Proteose peptone, 10.00; Dextrose, 2.00; Sodium chloride, 5.00; Disodium phosphate, 2.50.
And the final pH (at 250C) was 7.4+/-0.2.

9 dilutions of each drug were done with BHI for MIC determination. In the initial tube,
20 μL of the drug was added to the 380 μL of BHI broth. For dilutions, 200 μL of BHI broth
was added into the next 9 tubes separately. Then from the initial tube 200μL was transferred to
the first tube containing 200 μL of BHI broth. This was considered as 10-1 dilution. From 10-1
diluted tube, 200 μL was transferred to the second tube to make 10-2 dilution. The serial
dilution was repeated up to 10-9 dilution for each drug. From the maintained stock cultures of
required organisms, 5 μL was taken and added into 2 mL of BHI broth. In each serially diluted
tube, 200 μL of above culture suspension was added. The tubes were incubated for 24 hours
and observed for turbidity.
2.7. Molecular modeling/Docking studies
The 3D structure of the organic ligand was generated using the SKETCH module of
SYBYL package (Tripos Associates, St. Louis, MO, USA). The geometry optimization of the
organic ligand was done with the help of standard Tripos force field [29] using a distance
dependent-dielectric function, energy gradient of 0.001 kcal/ mol and Gastriger-Huckel as the
electrostatics. Conformations were minimized with Tripos force field and atomic charges
were calculated using Gastriger-Huckel method. Whereas the coordinates of all the complexes
were taken from their respective crystal structure as a CIF file and were converted to the PDB
format using Mercury software [30].
Molecular docking was used to clarify the binding mode of the compounds to provide
straightforward information for further structural optimization. Surflex-Dock that adopted an
empirical scoring function and a patented searching engine [31, 32] was employed for
molecular docking. The target protein structure was obtained from the crystal structure
of mycobacterium tuberculosis enoyl reductase complexed with N-(5-chloro-2-
methylphenyl)-1-cyclohexyl-5-oxopyrrolidine-3-carboxamide (PDB ID: 4U0K)[33] at
a resolution of 1.9 A˚ which was extracted from the Brookhaven Protein Database (PDB
http://www.rcsb.org/pdb). The proteins were prepared for docking by adding polar hydrogen
atom with Gasteiger-Huckel charges and water molecules were removed. And other
miscellaneous parameters were assigned with the default values given by the software.
3. Results and discussion
3.1. Synthesis
The ligand precursor 2-hydrazinobenzimidazole has been prepared by a new efficient
synthetic route, which involved the conversion of 2-mercaptobenzimidazole into 2-
bromobenzimidazole. Synthesis of the newly designed ligand along with its metal complexes
has been described in experimental section.

3.2. Spectral characterization
In the IR spectra (SI-S.1), the free ligand shows a relatively sharp band at 3440 cm-1.
This is assignable to υ(O-H) of the ligand where the hydrogen atom of the hydroxyl group is
hydrogen bonded [34]. This band has significantly broadened in all the complexes, indicating
the coordination of oxygen atom without deprotonation. The band at 1020 cm-1, which is due
to υ(C-O) has shown a significant positive shift in all the complexes due to the coordination of
oxygen. The ligand has shown a sharp intense band at 1637 cm-1 and is assigned to the υ(C=N)
of imine. The sharp intense band at 1578 cm-1 is assignable to υ(C=N) of benzimidazole ring.
In the complexes, these two bands have given a coupled vibration with decreased intensity and
significant negative shift, indicating the coordination of azomethine as well as ring nitrogen
[35]. A peak at 3246 cm-1 in the ligand, which is due to υ(N-H), has suffered from low energy
shift in all the complexes [36]. This observation again confirms the coordination of
azomethine nitrogen. The very sharp band at 1384 cm-1 in the case of [ZnL2](NO3)2 is
characteristic of nitrate counterions [37]. The similarity pattern observed in the spectra of
[CoL2]Cl2 and [NiL2]Cl2 suggests the similarity in structures. Further, the appearance of new
bands in the region of 520-560 and 400-490 cm-1 are evidencing the newly formed M-N and
M-O bonds in all the complexes [38]. Conclusively this suggests NNO, tridentate behavior of
the ligand.
1H NMR studies have been carried out for the ligand and diamagnetic zinc complex in
the region of 0-16 δ ppm. The spectrum of L (SI-S.2) has shown two broad down field
singlets. The broad singlet at 11.36 ppm is due to hydrogen of ring nitrogen whereas the other
1
broad singlet at 10.22 ppm is assignable to hydrazine N-H [39]. In the H NMR of the
[ZnL2](NO3)2 (SI-S.3), these two peaks have merged and given a broad peak around 12 ppm.
A triplet at 4.88 ppm is due to the hydroxyl group, which has coupled with methylene protons.
Coordination of hydroxyl group to the metal center has resulted in the downfield shift of this
peak to 3.13 ppm. In addition, coordination has also interrupted the possible coupling. In the
ligand, methylene protons have resonated at 4.04 ppm as a doublet. Deshielding of this to 4.30
ppm in the complex, reasonably accounts the shielding of coordinated oxygen atom [40]. The
singlet at 1.88 ppm, which is due to the methyl group of the ligand has shifted to 2.15 ppm in
the complex. In ligand as well as in complex, the four aromatic protons have resonated in two
sets in the expected aromatic region. Triplet at 1.015 and quartet centered at 3.40, undoubtedly
account for the ethanol solvation in the complex.
The electronic spectra of the ligand, as well as complexes, were recorded in DMF
solvent. The strong absorption in the range of 250-280 nm is ascribed to intra-ligand π → π*
transitions. The band has remained almost unchanged in the complexes. The n → π* transition
of azomethine functionality is observed between 300-350 nm and has suffered bathochromic

shift upon complexation. This is an indication of coordination of imine nitrogen to the metal
ions.
The [CoL2]Cl2 has shown its lowest energy transition around 921nm which is
4
4
assignable to T1g → T2g(ν1). The other two transitions observed around 798 and 453 nm are
4
4
4
4
consistent with the energies of, T1g → A2g(ν2) and T1g → T1g (P) (ν3), octahedral transitions
for the [CoL2]Cl2. The d-d transitions in [NiL2]Cl2 are observed around 924, 601 and 453 nm.
3
3
3
3
3
3
These are assignable to A2g → T2g (ν1), A2g → T1g(ν2) and A2g → T1g (P)(ν3) transitions,
which are in support of octahedral geometry of the complex. Absorption spectrum of copper
complex has given a d–d electronic band at 761 nm. Absorptions in this region are typical of
species with square pyramidal geometry around the Cu(II) ions [41].
3.3. Mass fragmentation
The EI mass spectrum of the L (SI-S.5) has shown the molecular ion peak [M]+ at m/z
204. Further, the intense peak at 173, is due to the loss of a CH2OH fragment of the ligand
indicating the ease of cleavage of this C-C bond. The ESI mass spectra of all the complexes
have shown several peaks due to the molecular cations of the various fragments formed during
electrospary ionization [35]. The intense peak at 205, in all the complexes, is due to the ligand
fragment [L+H]+. The ESI-MS of [NiL2]Cl2 has shown a peak at 465, corresponding to [NiL2-
H]+; and the base peak at 233, corresponding exactly to the m/z of [NiL2]2+. Similarly the
intense peaks at 466 and 233.5 in [CoL2]Cl2 are attributed to [CoL2-H]+ and [CoL2]2+
respectively. The peak at 119 in this complex is due to the protonated benzimidazole
fragment. ESI-MS of [ZnL2](NO3)2 has given a peak at 472, due to the [ZnL2-H]+. In
[CuLCl2], in addition to the peak at 266 due to [CuL-2Cl-H]+, the base peak is observed at m/z
307. This accounts for the mass of the species formed by the loss of CH2OH fragment from
the molecule and confirms the ascribed ligand to metal ratio.
3.4. Thermal analysis
All the complexes were studied for TG and DT analysis over the temperature range of
25-10000C under nitrogen atmosphere. The thermal decomposition pattern of [CuLCl2] and
[ZnL2](NO3)2 (SI-Fig.1&2) are dealt in detail.
[CuLCl2] has remained thermally stable without any loss of weight up to a
temperature of 1600C, showing the absence of any lattice held molecules. The weight loss of
about 9.3% (Calc. 9.4%) in the range of 160-1900C is due to the loss of a methanol fragment
of the ligand. This is clearly evidenced in DTA curve in the form of an exothermic peak at 185
0C. The remaining part of the ligand has decomposed gradually with the increase in
temperature.

The initial weight loss of about 7% (Calc.7.1%) in [ZnL2](NO3)2 is due to the loss of
an ethanol molecule. Further in the temperature range of 228-3100C, the complex has lost
about 30% (Calc. 29.2%) of its weight which is due to the combined loss of two nitrate
counter-ions along with 2 methanol fragments of the ligand. This process is further supported
by exothermic peaks in DTA curve at 237 and 2790C. Above 3100C the complex has gradually
lost its weight due to the decomposition of ligand moiety.
The TG and DT analytical data of [CoL2]Cl2 and [NiL2]Cl2 are in good agreement with
ascribed structures.
3.4. Crystal structures
Single crystals of all the complexes suitable for X-ray diffraction studies were grown by slow
evaporation technique. The structures of [CoL2]Cl2, [CuLCl2] and [ZnL2](NO3)2 has been studied in
detail. Asymmetric units of complexes showing 50% displacement ellipsoids along with the
numbering scheme are shown in fig. 1-3. Selected bond distances and bond angles are tabulated in
tables 2-5.
Fig.1 Asymmetric unit of [CoL2]Cl2 showing 50% displacement ellipsoids.
Fig.2 Asymmetric unit of [CuLCl2] showing 50% displacement ellipsoids.

Fig.3 Asymmetric unit of [ZnL2](NO3)2 showing 50% displacement ellipsoids.
Table 2. Selected Bond lengths [Å] and angles [°] for [CoL2]Cl2
N(1)-Co(1)
2.079(3)
2.078(3)
N(4)-Co(1)
N(5)-Co(1)
2.096(3)
N(8)-Co(1)
2.079(2)
O(1)-Co(1)
2.182(2)
O(2)-Co(1)
2.151(2)
N(4)-Co(1)-N(8)
N(4)-Co(1)-N(1)
N(8)-Co(1)-N(1)
N(4)-Co(1)-N(5)
N(8)-Co(1)-N(5)
N(1)-Co(1)-N(5)
N(4)-Co(1)-O(2)
N(8)-Co(1)-O(2)
N(1)-Co(1)-O(2)
N(5)-Co(1)-O(2)
N(4)-Co(1)-O(1)
N(8)-Co(1)-O(1)
N(1)-Co(1)-O(1)
N(5)-Co(1)-O(1)
O(2)-Co(1)-O(1)
169.30(10)
77.53(10)
112.13(10)
107.60(10)
77.18(10)
93.50(10)
101.48(10)
74.06(10)
93.28(9)
150.91(10)
74.31(10)
95.67(9)
151.59(10)
98.51(10)
88.63(9)
Table 3. Selected Bond lengths [Å] and angles [°] for [CuLCl2]
N(1)-Cu(1)
N(3)-Cu(1)
O(17)-Cu(1)
Cl(1)-Cu(1)
1.989(2)
1.959(2)
2.0226(19)
2.5273(6)

Cl(2)-Cu(1)
2.2379(7)
80.32(8)
N(3)-Cu(1)-N(1)
N(3)-Cu(1)-O(17)
N(1)-Cu(1)-O(17)
N(3)-Cu(1)-Cl(2)
N(1)-Cu(1)-Cl(2)
O(17)-Cu(1)-Cl(2)
N(3)-Cu(1)-Cl(1)
N(1)-Cu(1)-Cl(1)
O(17)-Cu(1)-Cl(1)
Cl(2)-Cu(1)-Cl(1)
152.81(8)
76.44(8)
100.90(6)
159.80(6)
96.19(6)
100.22(6)
98.56(6)
97.04(6)
101.02(2)
Table 4. Selected Bond lengths [Å] and angles [°] for [ZnL2](NO3)2
Zn-N(4)
2.0636(19)
2.0731(19)
2.1243(19)
2.1325(19)
2.163(2)
Zn-N(8)
Zn-N(5)
Zn-N(1)
Zn-O(1)
Zn-O(2)
2.1912(17)
95.69(8)
N(4)-Zn-N(8)
N(4)-Zn-N(5)
N(8)-Zn-N(5)
N(4)-Zn-N(1)
N(8)-Zn-N(1)
N(5)-Zn-N(1)
N(4)-Zn-O(1)
N(8)-Zn-O(1)
N(5)-Zn-O(1)
N(1)-Zn-O(1)
N(4)-Zn-O(2)
N(8)-Zn-O(2)
N(5)-Zn-O(2)
N(1)-Zn-O(2)
O(1)-Zn-O(2)
114.26(7)
76.17(7)
76.63(7)
105.47(7)
168.96(8)
148.39(7)
95.91(8)
97.05(7)
71.96(7)
94.07(7)
149.44(7)
73.41(7)
104.94(7)
90.66(7)
[CoL2]Cl2 has crystallized in the monoclinic crystal system with P21/n space group.
The structure of [CoL2]Cl2 contains [CoL2]2+ cation along with two chloride ions, without any

solvents of crystallization. Each ligand is coordinated to the central metal ion in an NNO
tridentate fashion with the benzimidazole-N (N1 and N5), imine-N (N4 and N8) and
hydroxyl-O (O1 and O2) as donor atoms. A dihedral angle of 87.1° is observed between the
mean planes of two ligands, in which two azomethine nitrogens (N4 and N8) reside trans to
each other whereas the other two donor sites (N1,N5 and O1,O5) have remained mutually cis
to each other. The ligand has formed two five-membered chelate rings with the metal center.
The O-Co-N and N-Co-N bite angles in case of both the ligands fall around 74° and 77°
respectively indicating significant deviation from ideal octahedral geometry in the complex.
The complex structure is stabilized by hydrogen bonding interactions between chloride
ions and the complex cations as depicted in the fig. 4. The first chloride (Cl1) ion is hydrogen
bonded to N-H hydrogens of benzimidazole ring and N-H of hydrazone functionality of the
same ligand with a bond distance of 2.56 Å and 2.43 Å respectively. The second chloride ion
(Cl2) has involved in hydrogen bonding with the hydroxyl group of the ligand with a bond
distance of 2.50 Å. This chloride ion has even made a hydrogen bond with N-H hydrogen of
benzimidazole ring with a bond distance of 2.22 Å.
Fig.4 Hydrogen bonding in [CoL2]Cl2
.
[CuLCl2] has crystallized in monoclinic crystal system in the C2/c space group. The
structure of [CuLCl2] contains a neutral complex molecule without any solvents of
crystallization. The ligand is coordinated to the central metal ion in an NNO tridentate fashion
with the benzimidazole-N (N3), imine-N (N1) and hydroxyl-O (O17) as donor atoms. In
addition, two chloride ions have coordinated; resulting in a penta coordinated tetragonally
distorted square pyramidal complex. The ligand has formed two five-membered chelate rings
with the metal center. The bond angles have deviated significantly from 900 , indicating the
deviation from ideal square pyramidal geometry. The verified axial (Cu1-Cl1) distance 2.52
Å is considerably longer than the basal (Cu1-Cl2) distance 2.23 Å in the structure, as
ascertained by Reedijk’s τ factor of 0.002 [42]. (τ = 0 for a square pyramid, and τ = 1 for a
trigonal bipyramid) [43].
[CuLCl2] is also stabilized by hydrogen bonding interactions of chloride ligand; which
has given a layered arrangement of complexes as depicted in fig.5. The equatorial chlorides

(Cl2) and hydroxyl hydrogens of two adjacent molecules of the same layer are involved in
hydrogen bonding with a bond distance of 2.21 Å. The axial chlorides (Cl1) have made bonds
with 2 adjacent molecules of the next layer, using benzimidazole N-H of one molecule and
hydrazide N-H of the other with a bond distance of 2.46 and 2.30 Å respectively.
Fig.5 Hydrogen bonding in [CuLCL2]
.
[ZnL2](NO3)2 has crystallized in triclinic crystal system with P-1 space group. The
structure of [ZnL2](NO3)2 contains [ZnL2]2+ cation along with two nitrate ions and an ethanol
molecule as solvent of crystallization. The coordination behaviour and geometrical aspects of
the [ZnL2](NO3)2 resembles with that of [CoL2]Cl2.
[ZnL2](NO3)2 is also stabilized by several hydrogen bonding interactions among complex
cation, nitrate ions and ethanol. First nitrate ion (N11) is hydrogen bonded to hydrazide N-H of one
molecule and ring N-H of the other molecule with the help of two different oxygen atoms. The
corresponding bond distances are 2.09 and 2.26 Å respectively. Simultaneously these two oxygens are
even interacting with the hydroxyl hydrogens of the third molecule, with the bond distances of 2.03
and 2.09 Å respectively. Whereas in the second nitrate ion (N12), one oxygen is hydrogen bonded to
hydroxyl hydrogen of one molecule and with the other oxygen it is interacting with benzimidazole N-
H and hydroxyl hydrogen of ethanol. The bond distances are 1.89, 2.26 and 1.86 Å respectively. The
oxygen (O13) of ethanol is accepting two bonds with hydrazide and benzimidazole N-Hs of the same
ligand, at a distance of 1.86 and 2.59 Å respectively.
Fig.6 Hydrogen bonding in [ZnL2](NO3)2

3.5. Cyclic voltammetry and conductivity
All complexes were studied for their electrochemical behavior by cyclic voltammetric
experiments at room temperature. The experiments were carried out in oxygen-free conditions in the
potential range of -1.00 to +1.00 V, using glassy carbon working electrode, a platinum counter
electrode and Ag/Ag+ reference electrode in DMF with varied scan rates. The copper complex is
found to be electrochemically active in the scanned range whereas the other complexes are found to
be electrochemically innocent. The voltammogram of copper complex is given in fig.7. The copper
complex has exhibited redox process corresponding to Cu(II)/Cu(I) couple with a cathodic peak at Epc
= 0.42 V, corresponding to Cu(II)/Cu(I) and respective anodic peak for Cu(I)/Cu(II) at Epa = 0.51 V.
The value of Δ Ep is more than 59 mV, indicating quasi-reversible redox process. The peak potential
dependency on scan rates and value (~1) for Ia/Ib (ratio of oxidative to reductive peak currents)
indicates simple one electron transfer [44].
The molar conductivity values for [CoL2]Cl2, [NiL2]Cl2 and [ZnL2](NO3)2 are above 200
Ohm-1 cm2 mol-1 indicating the 1:2 electrolytic nature of the complex[40], while [CuLCl2] being non-
electrolytic in nature.
Fig.7. Voltammogram of [CuLCl2]
3.6. In vitro growth inhibition of H37Rv
The drug-susceptible strain of M. tuberculosis, H37Rv[45] was used to determine the growth
inhibitory activity of ligand, complexes as well as streptomycin using microplate Alamar blue assay
(MABA). Results are tabulated in table 5.
Table 5. In vitro MIC values of synthesized compounds (in µg/mL)
Sample
M. tuberculosis
(H37Rv)
S. aureus
E. coli
A. niger
C. albicans
6.25
25
25
50
50
25
50
50
50
50
50
50
[CoL2]Cl2
[NiL2]Cl2
[CuLCl2]
50
6.25
12.5

25
25
25
1.6
3.12
-
50
50
25
-
25
50
-
25
50
-
[ZnL2](NO3)2
L
6.25
-
Streptomycin
Fluconazole
8
16
The efficacies of all synthesized compounds along with the standard
streptomycin/Fluconazole for the growth inhibition of four different microbes of the wide
taxonomical range were tested using the microbial strains of Staphylococcus aureus, Escherichia coli,
Aspergillus Niger and Candida albicans. Results are tabulated in table 3. The results though
unexpected, were significant due to ceased growth inhibition of tested microbes in comparison with
H37Rv. The MIC values of new complexes for S.aureus falls in the range of 25-12.5 µg/mL, whereas
for E.Coli the MIC value is found to be ranging up to 50µg/mL. These values are sufficiently higher
than the standard drug streptomycin which inhibits the S. aureus growth, even at 3.12µg/mL . The
MIC values for tested fungal strains are beyond 25µg/mL,which makes the strains resistant towards
the tested compounds even at higher concentrations than the standard fluconazole whose MIC is
sufficiently low towards tested fungi.
These results are significant in bringing the selectivity towards the growth inhibition of
H37Rv by metal insertion. Especially cobalt and copper complexes are found to be selectively active
against TB strain H37Rv[46] and have inhibited the growth of the species even at a concentration as
low as 6.25 µg/m, while the same being less active against other tested microbes. Notably, this kind of
selectivity is not observed in the case of bare ligand or even in the standard drug streptomycin.
The specific differences in the growth inhibiting potencies of the complexes of same ligand
system with different metal ions can be explained on the basis of Overtones concept of cell
permeability. The Co (II) ion bears lowest dipole moment, which could be related to its excellent
activity than other complexes. The decrease in dipole moment eventually reduces polarity and hence
increases the lipophilic nature of the complex, favoring the efficient permeation through lipid layer of
the microorganism [47]. The ligand was chosen as a design tool to produce mononuclear complexes,
with hydrophilic ‘cores’ and hydrophobic exteriors. Such complexes are water-soluble and capable of
facile hydrolysis making such complexes potential pro-drugs, which when coupled with the redox
properties of the metals complexed, is a strong approach to new metal-based therapeutics [48].
3.7. Molecular modeling/Docking studies
To investigate the mechanism of microbial growth inhibition, the effect of metal ions and
detailed intermolecular interactions between the synthesized compounds and microbial target
receptors, molecular docking studies were performed on enoyl acyl carrier protein reductase of M.
tuberculosis H37Rv. This enzyme is one of the key enzymes involved in the mycobacterial fatty acid

elongation cycle and has been validated as an effective antimicrobial target [49]. The binding domain
identified to accommodate is large enough to hold the synthesized molecules although these
molecules occupy slightly a larger volume. The possibility of larger molecular volumes resulting in
low docking scores is due to the fact that the size of the binding pocket being smaller than the
molecular volumes. The copper complex possessing relatively small volume due to its geometry,
coordinated halides and single ligand has shown more binding efficiency towards the target site. The
predicted binding energies of the compounds are listed in table 6.
Table 6. Surflex Docking score (kcal/mol) of the synthesized compounds
Compounds
C
Score
2.55
Crash
Score
-0.28
Polar
Score
D
Score
PMF
Score
G Score
Chem
Score
-19.21
[CoL2]Cl2
[NiL2]Cl2
[CuL]Cl2
[ZnL2](NO3)2
L
1.02 -7019.61 30.23 -99.14
0.70 -5383.20 0.79 -116.64
3.03 -2265.29 -4.63
0.00 -6614.84 15.63 -155.34
2.19 -1088.59 -3.02 -81.47
2.22
3.15
2.79
2.67
-0.38
-0.26
-0.65
-0.34
-19.33
-20.02
-22.31
-14.54
-80.64
The molecules showed consensus scores in the range of 2.22-3.15, indicating the summary
of all forces of interactions between the compounds and protein. [CuLCl2] has shown relatively high
C (consensus) scores showing the affinity of this molecule in binding the active site of the receptor.
Crash-scores are revealing the inappropriate penetration into the binding site. The copper and cobalt
complexes which are showing the crash scores close to zero are favorable, while the high negative
value in other cases is indicating penetration. The positive value of polar scores is indicating the
significant contribution of the polar interactions to the total score. The zero polar score in the case of
[ZnL2](NO3)2 may be useful for excluding docking results since it makes no significant hydrogen
bonds. The high value of D-score in the case of cobalt complex is due to the charge and van der Waals
interactions between the protein and the ligand [50]. Further, this is in accordance with the overtones
concept of cell permeability, which in turn explains the observed activity of the cobalt complex in
comparison with the other complexes. The PMF-scores in the case of complexes indicates more
Helmholtz free energies of interactions for protein-molecule atom pairs (Potential of Mean Force,
PMF)[51] than in the case of the free ligand. The G-score is showing hydrogen bonding, complex
(molecule-protein), and internal energies,[52] while the Chem-score points for H-bonding, lipophilic
contact, and rotational entropy, along with an intercept term [53].
The interaction of [CuLCl2] with the enzyme is depicted in Fig. 8 and Fig. 9, showing
three hydrogen bonding interactions, among which two are raised from the hydroxyl group.
The oxygen atom of the hydroxyl group of [CuLCl2] is involved in H-bonding interaction with
the hydrogen of threonine 386 (H-O----H-THR; 2.30 Å) and the hydrogen atom of hydroxyl

group makes an interaction with the oxygen atom of valine 373 (O-H ----O-VAL373; 2.05 Å).
The third hydrogen bonding interaction has raised from the hydrazide N-H with the oxygen
atom of threonine 386 (N-H----O-THR386; 1.73 Å). Fig.10 and 11 depict the two interactions
of the ligand with the active site of the enzyme. The hydrogen atom of the hydroxyl group of
ligand has interacted with valine 371 (O-H----O-VAL371; 1.91 Å) and the benzimidazole
ring-N is hydrogen bonded to the oxygen atom of threonine 386 (N-H----H-THR386; 2.01 Å).
Fig.8 Docking poses of the [CuLCl2] with amino acid residues at the active site of the enzyme.
Fig.9 Docking poses of the [CuLCl2] showing the distance between the amino acids with the
interacted atoms.
Fig.10 Docking poses of the ligand with amino acid residues at the active site of the enzyme.

Fig.11 Docking poses of the ligand showing the distance between the amino acids with the
interacted atoms.
4. Conclusions
In the present work, a newly designed benzimidazole based Schiff base ligand 2-(2-
(1H-benzo[d]imidazol-2-yl)hydrazono)propan-1-ol
has
been
synthesized
via
2-
hydrazinobenzimidazole. The organic motif binds the dipositive metal centers in NNO
tridentate mode through benzimidazole-N, azomethine-N and hydroxyl-O atoms respectively.
Analytical and spectroscopic data for the metal complexes indicate a 1:1 (M:L) stoichiometry
for copper and 1:2 for the remaining complexes. Except the non-electrolytic copper complex,
all other complexes are found to be 1:2 electrolytes. Co(II), Cu(II) and Zn(II) complexes have
crystallized in P21/n, C2/c and P-1space groups respectively. SC-XRD structures of Co(II),
and Zn(II) complexes reveal that the metal center is coordinated in an N4O2 core by a
tridentate ligand in a meridional fashion, and adopts a distorted octahedral geometry. Whereas
the Cu(II) complex has adopted distorted square pyramidal geometry. The complexes are
stabilized by intermolecular hydrogen bonding interactions. The copper complex, was
electrochemically active in the working potential range, showing quasi-reversible redox
system. In addition, the ESI-mass and thermal analysis of the copper complex are showing the
presence of an activated C-C bond, which is of particular interest in catalysis, for future
studies. Cobalt as well as copper complexes have emerged to be potent growth inhibitors of
TB strain H37Rv and have inhibited the growth of the species even at a concentration as low
as 6.25 µg/mL. The MIC value for other microbial strains is beyond 25µg/mL which makes
the strains resistant towards the tested compounds even at higher concentrations, bringing
selectivity towards the growth inhibition of H37Rv by metal insertion. This result would
create a future interest in bringing the metal based target specificity of existing drugs.
Molecular modeling of the compounds with the molecular target site of enoyl acyl carrier
protein reductase of M. tuberculosis H37Rv revealed that the molecules fit in the active site of
the receptor. Consensus scores for the complexes are in the range of 2.22-3.15. Copper
complex which emerged with high C-score of 3.15 is shown to be a better antitubercular agent
than bare parent organic motif. This docking result of copper complex is in agreement with the
observed MIC value.

Appendix A. Supplementary data
CCDC 1443163, 1459338 and 1454181 contains the supplementary crystallographic data for
[CoL2]Cl2 [CuLCl2] and [ZnL2](NO3)2. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
The authors thank USIC, Karnatak University, Dharwad, for providing spectral
facilities. Recording of ESI-mass spectra from CDRI-Lucknow is greatly acknowledged. SC-
XRD data collected from IOE-University of Mysore is also greatly acknowledged. One of the
authors (Vinayak Kamat) is thankful to Department of Science & Technology for providing
financial assistance under INSPIRE fellowship program and to UGC-New Delhi for JRF.
References
[1] K.T. Mahmudov, M.N. Kopylovich, A.J.L. Pombeiro, Coordination Chemistry Reviews 257 (2013) 1244-1281.
[2] S. Shit, S. Sen, S. Mitra, D.L. Hughes, Transition Metal Chemistry 34 (2009) 269-274.
[3] P.M. Vimal Kumar, P.K. Radhakrishnan, Polyhedron 29 (2010) 2335-2344.
[4] C.-M. Che, F.-M. Siu, Current Opinion in Chemical Biology 14 (2010) 255-261.
[5] C.X. Zhang, S.J. Lippard, Current Opinion in Chemical Biology 7 (2003) 481-489.
[6] K. Irena, B. Stefan, Current Medicinal Chemistry 20 (2013) 4508-4539.
[7] D. C. Crans, A. D. Keramidas, S. S. Amin, O. P. Anderson, S. M. Miller, Journal of the Chemical Society, Dalton
Transactions (1997) 2799-2812.
[8] D.C. Crans, The Journal of Organic Chemistry 80 (2015) 11899-11915.
[9] J.C. Pessoa, S. Etcheverry, D. Gambino, Coordination Chemistry Reviews 301–302 (2015) 24-48.
[10] C. Santini, M. Pellei, V. Gandin, M. Porchia, F. Tisato, C. Marzano, Chemical Reviews 114 (2014) 815-862.
[11] Z.H. Chohan, C.T. Supuran, A. Scozzafava, Journal of Enzyme Inhibition and Medicinal Chemistry 19 (2004) 79-84.
[12] J. Joseph, K. Nagashri, G.B. Janaki, European Journal of Medicinal Chemistry 49 (2012) 151-163.
[13] K. Kumar, D. Awasthi, S.-Y. Lee, I. Zanardi, B. Ruzsicska, S. Knudson, P.J. Tonge, R.A. Slayden, I. Ojima, Journal of
Medicinal Chemistry 54 (2011) 374-381.
[14] C. Gill, G. Jadhav, M. Shaikh, R. Kale, A. Ghawalkar, D. Nagargoje, M. Shiradkar, Bioorganic & Medicinal Chemistry
Letters 18 (2008) 6244-6247.
[15] J. Camacho, A. Barazarte, N. Gamboa, J. Rodrigues, R. Rojas, A. Vaisberg, R. Gilman, J. Charris, Bioorganic & Medicinal
Chemistry 19 (2011) 2023-2029.
[16] D.G. Kokare, K. Naik, A. Nevrekar, A. Kotian, V. Kamat, V.K. Revankar, Applied Organometallic Chemistry (2016) n/a-
n/a.
[17] D.G. Kokare, V. Kamat, K. Naik, A. Nevrekar, A. Kotian, V.K. Revankar, Journal of Molecular Structure.
[18] A. Jamadar, A.-K. Duhme-Klair, K. Vemuri, M. Sritharan, P. Dandawate, S. Padhye, Dalton Transactions 41 (2012) 9192-
9201.
[19] G.J. Kharadi, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 79 (2011) 898-903.
[20] S.P. Bruker, Bruker AXS Inc., Madison, Wisconsin, USA.
[21] G. Sheldrick, Acta Crystallographica Section A 64 (2008) 112-122.
[22] A. Spek, Acta Crystallographica Section A 46 (1990) c34.
[23] C.F. Macrae, I.J. Bruno, J.A. Chisholm, P.R. Edgington, P. McCabe, E. Pidcock, L. Rodriguez-Monge, R. Taylor, J. van de
Streek, P.A. Wood, Journal of Applied Crystallography 41 (2008) 466-470.
[24] R.K. Verma, R. Mall, P. Ghosh, V. Kumar, Synthetic Communications 43 (2013) 1882-1895.
[25] V. Kamat, K. Naik, V.K. Revankar, Journal of Molecular Structure.
[26] M.V.N.d. Maria C. S. Lourenco, Alessandra C Pinheiro, Marcelle de L. Ferreira, Rasnisb B, Goncalves, Thais Cristina M
Nogneira, Monica A Peralta., ARKIVOC 15 (2007) 181-191.
[27] L. Collins, S.G. Franzblau, Antimicrobial Agents and Chemotherapy 41 (1997) 1004-1009.

[28] M.a.G. Schwalve, CRC Press (2007).
[29] M. Clark, R.D. Cramer, N. Van Opdenbosch, Journal of Computational Chemistry 10 (1989) 982-1012.
[30] V. Thamilarasan, A. Jayamani, N. Sengottuvelan, European Journal of Medicinal Chemistry 89 (2015) 266-278.
[31] A.N. Jain, Journal of Computer-Aided Molecular Design 10 427-440.
[32] A.N. Jain, Journal of Medicinal Chemistry 46 (2003) 499-511.
[33] X. He, A. Alian, R. Stroud, P.R. Ortiz de Montellano, J Med Chem 49 (2006) 6308-6323.
[34] H.H. Freedman, Journal of the American Chemical Society 83 (1961) 2900-2905.
[35] A. Kamath, S.P. Netalkar, D. Gangaram Kokare, K. Naik, V.K. Revankar, Journal of Luminescence 132 (2012) 2763-2768.
[36] S.A. Galal, K.H. Hegab, A.S. Kassab, M.L. Rodriguez, S.M. Kerwin, A.-M.m.A. El-Khamry, H.I. El Diwani, European Journal
of Medicinal Chemistry 44 (2009) 1500-1508.
[37] S. Chandra, L.K. Gupta, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 60 (2004) 3079-3085.
[38] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds: Part A: Theory and Applications
in Inorganic Chemistry, Sixth Edition, 2008.
[39] I.H. Hall, N.J. Peaty, J.R. Henry, J. Easmon, G. Heinisch, G. Pürstinger, Archiv der Pharmazie 332 (1999) 115-123.
[40] P.P. Netalkar, S.P. Netalkar, V.K. Revankar, Applied Organometallic Chemistry 29 (2015) 280-289.
[41] A.B.P. Lever, Inorganic Electronic Spectroscopy (2nd ed.), Elsevier, Amsterdam, Amsterdam, 1984.
[42] W.A. Alves, S.A.d. Almeida-Filho, R.H.d.A. Santos, A. Paduan-Filho, A.M.d.C. Ferreira, Journal of the Brazilian Chemical
Society 15 (2004) 872-883.
[43] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, Journal of the Chemical Society, Dalton Transactions
(1984) 1349-1356.
[44] H. Okawa, M. Tadokoro, Y. Aratake, M. Ohba, K. Shindo, M. Mitsumi, M. Koikawa, M. Tomono, D.E. Fenton, Journal of
the Chemical Society, Dalton Transactions (1993) 253-258.
[45] B. Gold, H. Deng, R. Bryk, D. Vargas, D. Eliezer, J. Roberts, X. Jiang, C. Nathan, Nat Chem Biol 4 (2008) 609-616.
[46] A.E. Hoffman, M. DeStefano, C. Shoen, K. Gopinath, D.F. Warner, M. Cynamon, R.P. Doyle, European Journal of
Medicinal Chemistry 70 (2013) 589-593.
[47] R.R. Zaky, K.M. Ibrahim, H.M. Abou El-Nadar, S.M. Abo-Zeid, Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy 150 (2015) 40-53.
[48] L. Ronconi, P.J. Sadler, Coordination Chemistry Reviews 251 (2007) 1633-1648.
[49] K. Das, S. Nandi, S. Mondal, T. Askun, Z. Canturk, P. Celikboyun, C. Massera, E. Garribba, A. Datta, C. Sinha, T. Akitsu,
New Journal of Chemistry 39 (2015) 1101-1114.
[50] I.D. Kuntz, J.M. Blaney, S.J. Oatley, R. Langridge, T.E. Ferrin, Journal of Molecular Biology 161 (1982) 269-288.
[51] I. Muegge, Y.C. Martin, Journal of Medicinal Chemistry 42 (1999) 791-804.
[52] G. Jones, P. Willett, R.C. Glen, A.R. Leach, R. Taylor, Journal of Molecular Biology 267 (1997) 727-748.
[53] M.D. Eldridge, C.W. Murray, T.R. Auton, G.V. Paolini, R.P. Mee, Journal of Computer-Aided Molecular Design 11 425-
445.

Structures of Co(II), Cu(II) and Zn(II) complexes of 2-(2-(1H-benzo[d]imidazol-2-
yl)hydrazono)propan-1-ol