Synthesis, X-ray structure, theoretical investigation, corrosion inhibition and antimicrobial activity of benzimidazole thioether and theirs metal complexes

Article abstract of DOI:10.1016/j.poly.2016.08.045

Synthesis, characterization, corrosion inhibition as well as antimicrobial activity of the coordination compounds {Co(bbms)Cl₂}, {Zn(bbms)Cl₂}, {Co(btmb)Cl₂} and {Zn(btmb)Cl₂} containing benzimidazole thioether have been described. Co(bbms) and Zn(bbms) as well as Co(btmb) and Zn(btmb) are isostructural with space group Pbca and P21 respectively. The coordination polyhedron around the metal center for all complexes may be described as a quasi-regular tetragonal geometry. The corrosion inhibition study of these complexes for steel in 0.5?M H₂SO₄medium has been investigated using potentiodynamic polarization and EIS techniques. These later show the corrosion inhibition ability of the prepared complexes for steel in acid medium. A new procedure has been developed for antimicrobial assay using a solid tablet of the corresponding complexes. These later show moderate to significant antimicrobial activities against: Pseudomonas syringae, Staphylococcus aureus and Pichia caribbica. DFT/BP86 calculations have been carried out on the neutral complexes and on the monoanionic of (1) and (3) forms of singlet and triplet species. The optimized structures reproduce those observed experimentally, while the reduced ones undergo remarkable geometrical parameters variations.

Full text of DOI:10.1016/j.poly.2016.08.045

Accepted Manuscript
Synthesis, X-ray structure, theoretical investigation, corrosion inhibition and
antimicrobial activity of benzimidazole thioether and theirs metal complexes
Mehdi Bouchouit, Said Mohamed Elhadi, Mounira Kara Ali, Sofiane Bouacida,
Hocine Merazig, Nourreddine Kacem Chaouche, Aissa Chibani, Bachir
Zouchoune, Ali Belfaitah, Abdelmalek Bouraiou
PII:
S0277-5387(16)30414-4
DOI:
http://dx.doi.org/10.1016/j.poly.2016.08.045
POLY 12182
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
28 June 2016
21 August 2016
24 August 2016
Please cite this article as: M. Bouchouit, S. Mohamed Elhadi, M. Kara Ali, S. Bouacida, H. Merazig, N. Kacem
Chaouche, A. Chibani, B. Zouchoune, A. Belfaitah, A. Bouraiou, Synthesis, X-ray structure, theoretical
investigation, corrosion inhibition and antimicrobial activity of benzimidazole thioether and theirs metal complexes,
Polyhedron (2016), doi: http://dx.doi.org/10.1016/j.poly.2016.08.045
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Synthesis, X-ray structure, theoretical investigation, corrosion
inhibition and antimicrobial activity of benzimidazole thioether
and theirs metal complexes
a
a
b
a, c
Mehdi Bouchouit, Said Mohamed Elhadi, Mounira Kara Ali, Sofiane Bouacida,
a
b
a
a,c
Hocine Merazig, Nourreddine Kacem Chaouche, Aissa Chibani, Bachir Zouchoune, Ali
d
a*
Belfaitah, and Abdelmalek Bouraiou
a Unité de Recherche de Chimie de l’Environnement et Moléculaire Structurale, Université
des Frères Mentouri, Constantine 25000, Algérie
b Laboratoire de Mycologie, de Biotechnologie et de l’Activité Microbienne, Université des
Frères Mentouri, Constantine 25000, Algérie
c Département des sciences de la matière, Université Oum El Bouaghi, 04000 Oum El
Bouaghi, Algérie
d Laboratoire des Produits Naturels d’Origine Végétale et de Synthèse Organique, Université
des Frères Mentouri, Constantine 25000, Algérie
Correspondence (A. Bouraiou): bouraiou.abdelmalek@yahoo.fr; Tel.: +213-05-51-599-889;
Fax: +213-031-903-558
Keywords
Benzimidazole complexes; X-Ray determination structure; Corrosion inhibition;
Antimicrobial activity; Electronic structure.
Abstract
Synthesis, characterization, corrosion inhibition as well as antimicrobial activity of the
2 2 2 2
coordination compounds {Co(bbms)Cl }, {Zn(bbms)Cl }, {Co(btmb)Cl } and {Zn(btmb)Cl }
containing benzimidazole thioether have been described. Co(bbms) and Zn(bbms) as well as
Co(btmb) and Zn(btmb) are isostructural with space group Pbca and P21 respectively.
The coordination polyhedron around the metal center for all complexes may be described as a
quasi-regular tetragonal geometry. The corrosion inhibition study of these complexes for steel
2 4
in 0.5 M H SO medium has been investigated using potentiodynamic polarization and EIS
techniques. These later show the corrosion inhibition ability of the prepared complexes for
steel in acid medium. A new procedure has been developed for antimicrobial assay using a
solid tablet of the corresponding complexes. These later show moderate to significant

antimicrobial activities against: Pseudomonas syringae, Staphylococcus aureus and Pichia
caribbica. DFT/BP86 calculations have been carried out on the neutral complexes and on the
monoanionic of (1) and (3) forms of singlet and triplet species. The optimized structures
reproduce those observed experimentally, while the reduced ones undergo remarkable
geometrical parameters.
Introduction
Benzimidazole derivatives are reported to be physiologically and pharmacologically active
and have shown different biological activities such as antioxidant [1], antifungal [2],
antihelmintic [3], antitumoral [4], anti-inflammatory [5] and antimicrobial [6,7]. Furthermore,
benzimidazole derivatives can be also used as epoxy resin curing agents, catalysts, and
metallic surface treatment agents [8,9].
The ability of benzimidazole derivatives to form stable complexes with metal ions, had given
a place to a variety of metal-ligand coordination modes. Their reactions with metal salts have
played a significant role in the development of coordination chemistry [11-12]. Several
research teams have examined the coordination behavior of benzimidazole derivatives
towards transition metal ions [13,14] and others studies have explored the biological activity
of coordination compounds containing benzimidazole entity [15-17].
In other hand, benzimidazole derivatives are effective corrosion inhibitors for many metals.
The efficiency of these heterocyclic derivatives is due to the presence of high-electron-density
zone. These molecules types form an adsorbed protective film on the metal surface, which
leads to isolating the metal surface from the corrosive environment [18-20].
In this study, we report the synthesis of four benzazole thioether metal complex namely
{
Co(bbms)Cl
2
}(1), {Zn(bbms)Cl
2
} (2), {Co(btmb)Cl
2
} (3) and {Zn(btmb)Cl
2
} (4) and their
application for the first time as corrosion inhibitors on mild steel in 0.5 M H
2
SO . The crystal
4
structures of all compounds are extensively discussed and their corrosion inhibition activities
are examined using electrochemical impedance spectroscopy (EIS) and Tafel polarization.
The antimicrobial activities of the prepared compounds will be also evaluated.
In addition, in this study we endeavor to give an accurate description of the electronic
structure and the molecular bonding on a series of neutral and reduced complexes by means
of density functional theory (DFT/BP86) calculations (see Computational methods), which is
already established to be valuable in determining the electronic structures, the geometrical
parameters, bonding analysis and other properties from previous theoretical works of mono-
metallic complexes [21-26], and reproducing efficiently the experimental structures.

Experimental
General considerations
1
All chemicals reagents and solvents were of analytical grade and were used as received. H-
13
NMR and C-NMR spectra were recorded on Brüker Avance DPX250 spectrometers. The
melting point was determined using an Electrothermal IA9100 digital melting point apparatus.
UV spectra were recorded on UV/VIS Spectrophotometer Optizen 1220; IR spectra were
recorded on Shimadzu FT/IR-8201 PC spectrophotometer.
Synthesis of ligands
The bis((1H-benzo[d]imidazol-2-yl)methyl)sulfane: Ligand (bbms)
The bis((1H-benzo[d]imidazol-2-yl)methyl)sulfane (bbms) was prepared according to
modified literature methods [27], by using a mixture of 2-mercaptomethylbenzimidazole
(
164.2 mg, 1 mmol) and 2-chloromethylbenzimidazole (166.6 mg, 1 mmol) in MeOH and in
presence of MeONa (81 mg, 1.5 mmol). The cooled precipitates were collected by filtration.
–
1
Yield 67%; Yellow solid; m.p. 240 °C (m.p. 221 °C [28]); IR spectrum (KBr, ν cm ): 3409,
1
2
781, 2360, 1635, 1535, 1442, 1272, 1157, 1026, 856, 735; H NMR (250.13 MHz, DMSO-
1
3
d6) δ: 12.59 (s , 2H), 7.56-7.53 (m, 4H), 7.20-7.16 (m, 4H), 4.08 (s, 4H); C NMR (62.9
L
MHz, DMSO-d6) δ: 151.8, 138.8, 121.8, 114.9, 28.8.
The 2-((1H-benzo[d]imidazol-2-yl)methylthio)-1H-benzo[d]imidazole: Ligand (btmb)
The 2-((1H-benzo[d]imidazol-2-yl)methylthio)-1H-benzo[d]imidazole (btmb) was prepared
according to literature methods [29], by using a mixture of 2-mercaptobenzimidazole (150.2
mg, 1 mmol) and 2-chloromethylbenzimidazole (166.6 mg, 1 mmol) in MeOH and in
presence of MeONa (81 mg, 1.5 mmol). A yellow precipitate was formed, filtered and washed
with methanol. Yield 77%; Yellow solid; m.p. > 250°C (m.p. 250-257 °C [29]); IR spectrum
–
1
1
(
(
(
KBr, ν cm ): 3429, 2781, 1616, 1500, 1535, 1411, 1357, 1272, 1222, 856, 744; H NMR
13
250.13 MHz, DMSO-d6) δ: 7.55-7.46 (m, 4H), 7.20-7.11 (m, 4H), 4.78 (s, 2H); C NMR
62.9 MHz, DMSO-d6) δ: 152.9, 149.3, 140.7, 139,5, 125.3, 122.2, 116.5, 114.5, 32.5.
Synthesis of complexes
2
Synthesis of complex {Co(bbms)Cl } (1)
CoCl
2
,6H
2
O (1 mmol) were added with stirring to a solution of bbms (1 mmol) in 8 mL of
MeOH. The mixture was stirred for 18 hours. The blue precipitate 1 that formed was filtered
–
1
and dried in vacuo. Yield = 84%; m.p.=285-288°C; IR spectrum (KBr, ν cm ): 3444, 2356,

1
2
631, 1527, 1450, 1388, 1272, 1145, 1122, 1037, 744; UV-Vis (chloroform, λ (nm)): 220,
48, 276; Suitable crystals for X-ray diffraction of 1 were obtained from cold
dimethylformamide solution.
2
Synthesis of complex {Zn(bbms)Cl } (2)
The synthetic procedure of 2 was similar to that for 1, except that ZnCl
2
(1 mmol) was used
1
instead of cobalt chloride. The yellow solid 2 was obtained in 79% yield. m.p.=285°C; H
NMR (250 MHz, DMSO-d6) δ: 13.72 (s
L
, 2H), 8.32 (s
L L
, 2H), 6.9 (s , 2H), 7.43-7.40 (m, 4H),
1
3
4
1
1
.07 (s, 4H); C NMR (62.9 MHz, DMSO-d6) δ: 151.75, 139.1, 132.96, 124.34, 123.39,
–1
18.28, 112.59, 25.13; IR spectrum (KBr, ν cm ): 3436, 3174, 3136, 2773, 2360, 1608, 1527,
454, 1415, 1276, 1153, 752; UV-Vis (chloroform, λ (nm)): 224, 246, 276; Suitable crystals
for X-ray diffraction of 2 were obtained from cold dimethylformamide solution.
Synthesis of complex {Co(btmb)Cl } (3)
2
The synthetic procedure of 3 was similar to that for 1, except that btmb (1 mmol) was used
instead of bbms. The blue solid 3 in 81 % yield was obtained. m.p. > 300°C; IR spectrum
–1
(
(
KBr, ν cm ): 3444, 2985, 2360, 1624, 1415, 1276, 1222, 1149, 1056, 1013, 752. UV-Vis
chloroform, λ (nm)): 226, 250, 286; Suitable crystals for X-ray diffraction of 3 were obtained
from cold dimethylformamide solution.
Synthesis of complex {Zn(btmb)Cl } (4)
2
The synthetic procedure of 4 was similar to that for 1, except that btmb (1 mmol) ZnCl
2
(1
, respectively. The yellow solid 4 in 80 % yield
, 4H), 7.39-7.33
mmol) were used instead of bbms and CoCl
2
1
was obtained. m.p > 300 °C; H NMR (250.13 MHz, DMSO-d6) δ: 7.91 (s
L
–1
(
S
L
, 4H), 4.88 (s, 2H); IR spectrum (KBr, ν cm ): 3456, 2333, 1624, 1535, 1419, 1276, 1226,
1
153, 1056, 991, 910, 748. UV-Vis (chloroform, λ (nm)): 228, 282; Suitable crystals for X-
ray diffraction of 4 were obtained from cold dimethylformamide solution.
X-ray crystallography
The crystal was coated with Paratone oil and mounted on loops for data collection. X-ray data
were collected with a Bruker Apex II CCD area detector diffractometer with a graphite-
monochromated Mo-Kα radiation source (0.71073 Å) at 298 K. The reported structure was
solved by direct methods with SIR2002 [30] to locate all the non-H atoms which were refined
2
anisotropically with SHELXL97 [31] using full-matrix least-squares on F procedure from
within the WinGX [32] suite of software used to prepare material for publication.

All absorption corrections were performed with the SADABS program [33]. All the H atoms
were placed in the calculated positions and constrained to ride on their parent atoms. The
DIAMOND package and ORTEP-3 for Windows programs were used for generating figures
of structures [34,35]. Crystal data, structure refinement parameters., some intra and
intermolecular interactions hydrogen bonds, C-H…π and π−π stacking for compound 1-4 are
listed in Tables 1, 2 and 3.
Corrosion inhibition measurements
Preparation of Solutions
2 4
The acid solution of 0.5 M H SO was prepared by dilution of analytical grad 97-98% with
-3
distilled water. The concentration of the inhibitors employed was 5×10 M.
Steel Specimen
For galvanostatic and potentiodynamic polarization measurements were performed using a
cylindrical working electrode embedded with epoxy steel resin with an exposed surface area
2
of 0.64 cm . The chemical elements content of the working electrode was determined using
Philips Analytical MagiX-PRO X-ray Fluorescence Spectrometer (XRF) with the PW2540
vrc sample changer and SuperQ analytical software package. The relative percentage of the
elements content is: Al (0.919%), Si (0.351%), P (0.023%), S (0.048%), Mn (0.524%), Cu
(
0.938), Fe (97.197%). Before measurement, the working electrode was abraded with
different emery paper, from a coarse grade 400 and proceeding in steps to fine grade 2000,
degreased with ethanol, rinsed several times with distilled water, then dried.
The electrochemical measurements were carried out in a conventional cylindrical glass cell
equipped with a three-electrode system that consisted of a working electrode, a platine
counter electrode and a saturated calomel electrode (SCE) as the reference electrode.
Polarization and impedance measurements were performed using a
potentiostat/galvanostat/ZRA «GAMRY-Reference 3000». The electrochemical cell was kept
for 30 minutes to stabilize the steady-state potential before the EIS and potentiodynamic
polarization measurements were started. The polarization measurements were performed
-1
using a scan rate of 1 mV s in the potential range of -800 to -200 mV. Electrochemical
impedance spectroscopy (EIS) were performed at open circuit potential (Ecorr) over a
frequency range of 10 kHz to 10 mHz with AC signals of 10 mV peak-to-peak amplitude at
the open circuit potential. Various corrosion parameters and inhibition efficiency (IE %) are
listed in Tables 5 and 6.

Antimicrobial activity
The antimicrobial activity the prepared complexes 1-4 were evaluated in vitro for their
antimicrobial activity against Staphylococcus aureus : Sa (ATCC-25923), Klebsiella
pneumonia Kp (ATCC-700603), Pseudomonas Syringae Ps (Kc 311253) and Pichia
caribbica Pc (Kc 977491) as yeast. The two ligands bbms and bmtb were used for
comparison. Solid tablet of the tested compounds were used in this study and are prepared as
follow: The tested compound (1 mg) is added to 100 mg of peptone as adsorbing agent, and
then finely ground and mixed in a smooth agate mortar. This mixture is placed in special 6
mm evacuable pellet die, and then compacted under pressure of 1.5 Tons. Solid tablet of 6
mm diameter and a thickness of about 0.5 mm are obtained and are used within 60 minutes.
Microbial cells were swabbed on to nutrient medium (Mueller–Hinton Broth for bacteria and
YPG Medium for yeast) in petri plates and the solid tablet containing different compounds
were placed onto the agar using sterile forceps. The inoculated petri plates were incubated at
3
7 °C and 30 °C for 24 h for bacterial and yeast strains, respectively. Finally, the diameters of
the inhibition zone around each pellet were measured in millimeter. For comparison of
benzylpenicilline sodique (1 mg), adsorbed on 100 mg of peptone, was used as standard drug.
The results of the antimicrobial screening of the prepared compounds are listed in Table 7.
Computational methods
Density functional theory (DFT) calculations were carried out on the studied compounds
using the Amsterdam Density Functional (ADF) program [36], developed by Baerends and
co-workers [37-41]. Electron correlation was treated within the local density approximation
(
LDA) in the Vosko-Wilk-Nusair parametrization [42]. The non-local corrections of Becke
and Perdew (BP86) were added to the exchange and correlation energies, respectively [43-
6]. The numerical integration procedure applied for the calculations was developed by te
4
4
1
Velde et al. The atom electronic configurations were described by a triple-ζ Slater-type
orbital (STO) basis set for H 1s, C 2s and 2p, N 2s and 2p augmented with a 3d single-ζ
polarization for C and N atoms and with a 2p single-ζ polarization for H atoms. A triple-ζ
STO basis set was used for the Co and Zn transition metals 3d and 4s, augmented with a
single-ζ 4p polarization function for Co and Zn. A frozen-core approximation was used to
3
7-41
treat the core shells up to 1s for C, N, 3p for Co and Zn transition metals.
Full geometry
optimizations were carried out using the analytical gradient method implemented by Versluis
and Ziegler [47]. Spin-unrestricted calculations were performed for all the open-shell systems.
Frequencies calculations [48,49] were performed on all the studied compounds to check that

the optimized structures are at local minima. Representation of the molecular structures and
molecular orbitals were done using ADF-GUI [36].
Results and discussion
Synthesis
The bis((1H-benzo[d]imidazol-2-yl)methyl)sulfane (bbms) was synthesized following a
modified literature procedure starting from 2-chloromethylbenzimidazole and 2-
mercaptomethylbenzimidazole [27]. The 2-((1H-benzo[d]imidazol-2-yl)methylthio)-1H-
benzo[d]imidazole (btmb) was prepared according to literature procedure starting from 2-
mercaptobenzimidazole and 2-chloromethylbenzimidazole and its structure has been
confirmed by spectroscopic methods [29].
The complexes 1-4 have been reported previously in a few papers and their structures were
proposed spectroscopically or theoretically in other some cases [50-54]. However, no
structural confirmation using crystallographic study had been reported. Thus it was
considered of interest, in order to confirm and understand the three
dimensional structures of these complexes, to carry out an X-ray diffraction analysis. In this
context, we have adopted the following procedure for their preparation:
2
The ligands bbms and btmb were stirred in MeOH with MCl (1 equivalent of M=Co, Zn)
overnight at room temperature (Scheme 1). The solids metal (II) complexes were filtered off
and dried. All complexes are stable in the air, soluble in DMF and DMSO but insoluble in
water and other organic solvents. The organic part of complexes 2 and 4 were also confirmed
1
13
by H and C NMR. Crystals of complexes 1, 2, 3 and 4 were obtained by recrystallization in
DMF and the complexes structures are shown in Scheme 1 and Figure 1a-d.

n=0,1
H
N
H
N
S
n=1 bbms
n=0 btmb
N
N
MeOH
rt, overnight
ZnCl2
CoCl2
H
N
H
N
H
N
H
N
S
S
N
N
N
Co
N
Zn
CoCl2 ZnCl2
Cl
Cl
Cl
Cl
{Zn(btmb)Cl } (4)
2
{Co(bbms)Cl } (1)
2
H
N
H
N
H
N
H
N
S
S
N
N
N
Zn
N
Co
Cl
Cl
Cl
Cl
{Co(btmb)Cl } (3)
2
{Zn(bbms)Cl } (2)
2
Scheme 1. Synthesis of complexes 1, 2, 3, and 4
Crystal structures
All complexes were recrystallized and suitable crystals of 1, 2, 3 and 4 were grown in DMF
solution of the corresponding complexes. The X-ray crystallographic analysis confirmed their
respective structures and the refined X-ray crystal structures are shown in Figures 1a-d.
Crystal data and structural details of the prepared complexes are presented in Table 1.
Table 1
Crystallographic data and refinement parameters for 1-4.
{
Co(bbms)Cl
2
}
{Zn(bbms)Cl
2
}
{Co(btmb)Cl
(3)
2
}
{Zn(btmb)Cl
2
}
(1)
(2)
(4)
Formula
C
16
H
14
N
4
SCl
2
Co
C
16
H
14
N
4
SCl
2
Zn
C
15
H
12
N
4
SCl
2
Co
15 12 4 2
C H N SCl Zn
Formula weight
Crystal habit, color
Crystal system
Space group
a (Å)
424.2
Prism, Blue
430.64
410.18
416.64
Needle, Colorless
Orthorhombic
P bca
Prism, Blue
Monoclinic
Block, Colorless
Monoclinic
Orthorhombic
P bca
P 2
1
P 2
1
14.0899(7)
15.1625(6)
15.8182(7)
90
14.1241(3)
15.1797(3)
15.8011(3)
90
8.1661(16)
13.762(3)
14.614(3)
90
8.2890(5)
13.8148(8)
14.6318(9)
90
b (Å)
c (Å)
α (º)
β (º)
90
90
92.468(12)
92.058(4)

γ (º)
90
90
90
90
3
Volume (Å )
Z, Z'
3379.4(3)
8, 8
3387.75(12)
8, 8
1640.9(6)
2, 4
1674.42(17)
2, 4
-3
Density (calculated, g cm )
1.668
1.689
1.661
1.653
-1
Absorption coefficient (mm )
F(000)
1.46
1.894
1.501
1.913
1720
1744
828
840
Crystal size (mm)
0.09×0.14×0.15
2.36 - 25.04
20250
4031
0.03×0.04×0.13
2.58-27.71
16920
3956
0.11×0.15×0.19
2.79 - 31.06
17080
8836
0.09×0.11×0.14
2.46- 26.37
13897
6479
θ range for data collection (º)
Reflections collected
Independent reflections
R
int
0.0512
2873
0.0302
3060
0.0428
7210
0.0403
5128
Reflections with I ≥ 2σ(I)
Number of parameters
217
217
423
409
2
Goodness-of-fit on F
1.141
1.041
0.981
1.077
Final R indices [I ≥ 2σ(I)]
R indices [all data]
0.0514
0.0318
0.0382
0.0722
R
1
=0.0907,
R
1
= 0.0471,
R
1
=0.0539,
R
1
= 0.0911,
Largest difference peak and hole
2
wR =0.1027
2
wR = 0.0777
2
wR =0.0835
wR = 0.1913
2
-
3
(
Å )
0.658, -0.849
--
0.402, -0.327
--
0.606, -0.337
0.017(11)
1.821, -0.817
0.12(2)
Flack's Parameter
CCDC deposition no.
CCDC 1432478
CCDC 1432480
CCDC 1432479
CCDC 1432481
2 2
Crystal structure of {Co(bbms)Cl } (1) and {Zn(bbms)Cl } (2)
The complex 1 crystallizes in the orthorhombic crystal system (space group Pbca). The
compound {Co(bbms)Cl } (1) (Figure 1a) is a tetra-coordinate metal complex. The complex
contains one organic ligand of bis((1H-benzo[d]imidazol-2-yl)methyl)sulfane and the cobalt
II) is surrounded by two N-donor atoms and two chloride ligand. The cobalt(II) environment
2
(
exhibits a quasi-regular tetragonal coordination. The bond distances Co(1)–N(1) and Co(1)–
N(2) are 2.046 (4) Å and 2.036 (4) Å, respectively, while the distance Co(1)–Cl(1) is 2.2525
(
16) Å and the distance Co(1)–Cl(2) is 2.2507 (15) Å. Bond angles for N(1)–Co(1)–Cl(1) and
for Cl(1)–Co(1)–Cl(2) are 115.66 (12)° and 109.65 (6)°, respectively and the bond angle
N(1)–Co(1)–N(2) is 109.46 (16) Å (Table 1). The deviation of these values from the ideal
1
09° corresponding to a perfect tetragonal geometry indicates a distorted tetragonal geometry.
Bond lengths and angles are in the expected range [55-57].
In bis((1H-benzo[d]imidazol-2-yl)methyl)sulfane ligand, both benzimidazole rings, linked by
thiomethyl group, are quasiplanar and form between each other a dihedral angle of 44.74 (11)°.
The crystal packing can be described as alternating double layers along the b axis (at b=1/4
and b=3/4) parallel to (010) plane (Figure 2). These layers are connected with N-H…Cl and
C-H…S interactions resulting in the formation of two dimensional networks. Hydrogen bond

ꢁ
between amine moieties and chlorine atom form a chain with ꢀ (6) graph set motif [58,59].
ꢁ
Additional hydrogen-bonding parameters are listed in Table 2.
The packing is consolidated by slippest π−π stacking with centroid to centroid distance of
3
.601 (3) Å to 3.753 (3) Å and a weak intermolecular interaction C(12)–H(12)…Cg (N(1)-
C(1)-N(3)-C(7)-C(2)) with a distance of C…Cg is 3.660 (6) Å and the C-H…Cg angle of
33° (Table 3). These interactions link the molecule within the layers and also link layers
1
together and reinforcing the cohesion of the complex structure.
Compounds 1 and 2 are isostructure (Table 1). The asymmetric unit of 2 consists of
bbms ligand binds to one zinc(II) through the two amine nitrogen atoms (Figure 1b). The
zinc atom is tetrahedrally surrounded also by two chlorine atoms. The two chlorine atoms are
said to be joined by a covalent bond. The molecular structure is running in zigzag chain along
the a axis. The network is stabilized by two intermolecular interactions N-H…Cl between Cl
atoms and H atoms of N atoms of the nearest benzimidazole ring. Similarly, in this
compound, a weak C-H…Cl intramolecular interactions hydrogen bonds (Figure 3), C-H…π
intermolecular interactions and π−π stacking are observed (Table 2 and 3).

Fig. 1. Oak ridge thermal ellipsoid plots (ORTEP) of the molecular structures of 1, 2, 3 and 4
in the crystal and atom numbering scheme adopted (displacement ellipsoids at the 50 %
probability level; H atoms with arbitrary radii; blue: nitrogen, yellow: sulfur, green: chlorine).
Crystal structure of {Co(btmb)Cl
2 2
} (3) and {Zn(btmb)Cl } (4)
In 3, the compound crystallizes in the monoclinic crystal system (space group P2
1
) (Table 1,
Figure 1c). There are two crystallographic independent but similar molecules in the
asymmetric unit that we have labeled as molecule a and b (Figure 1c and Figure 4). The btmb
ligand who act as bidentate chelating ligand, consists of two benzimidazole unit attached
together with thiomethyl linker. Both molecules of Co(btmb)Cl (3) are refined with
2
disordered atoms of sulfur and carbon neighbors in the chain. Changes in a linker moiety,
such as methylthiomethyl vs thiomethyl, had a significant effect on the dihedral angles values
between the two benzimidazole entities (for compound 1: 44.74(11)°; for compound 3:
2
9.62(5)° in molecule a and 22.29(6)° in molecule b).
In the asymmetric unit of 3, the Co(II) is in slightly distorted tetrahedral environment. It is
surrounded by two N atoms from benzimidazole ring of organic ligand (Co(1a)-N(1a) =
2
.019(2) Å; Co(1a)-N(2a) = 1.998(3) Å; Co(1b)-N(1b)=2.000 (3) Å; Co(1b)-N(2b)=1.999(3)
Å) and two chlorine atoms [Co(1a)-Cl(1a) = 2.2622(9) Å; Co(1a)-Cl(2a) = 2.2430 (9) Å;
Co(1b)-Cl(1b) = 2.2607 Å; Co(1b)-Cl(2b) =2.2501(9) Å).
The structure of 3 is refined with disorder between S and C atoms with 0.37/0.63 ratio, using
part instruction of Shelx program [31]. The site occupancies of the major and minor
components of the disordered carbon and sulfur atoms are 0.37 and 0.63, respectively.
Compounds 3 and 4 are isostructure (Figure 1d). There are two crystallographic independent
molecules (Figure 1d). Complex 4, with a bidentate N donors ligand and two bounds
chlorines, possess a quasi-regular tetrahedral geometry about the Zn(II) centre with [Cl(1a)–

Zn(1a)–Cl(2a): 107.52(9)°; N(1a)–Zn(1a)–N(2a): 110.5(3)°; N(1a)–Zn(1a)–Cl(1a): 110.7(2);
Cl(1b)–Zn(1b)–Cl(2b): 112.39(9); N(1b)–Zn(1b)–N(2b): 108.8(3)°; N(1b)–Zn(1b)–Cl(1b):
1
10.43(19)°]. The ligand coordinates with the metal centre in its neutral form. Bond lengths
and angles are in the expected range [55-57]. Various intermolecular interactions such as N-
H…Cl, C-H…π and π-π contribute in the stability of the crystal packing (Figure 5, Tables 2
and 3).
Fig. 2. Alternating layers parallel to (010) plane of 1 at b=1/4 and b=3/4, viewed via a axis.
Hydrogen bonds are shown as red dashed lines (N–H…Cl and C-H...S) connecting these
layers.
Fig. 3. View of the crystal structure of 2 showing layers in zigzag along the a axis. Hydrogen
bonds are shown as red dashed lines (N–H…Cl) connecting these layers.

Fig. 4. View of the crystal structure of 3 showing double layers along the c axis connecting
via hydrogen bonds interactions shown as red dashed lines.
Fig. 5. Crystal packing of 4 viewed via c axis showing hydrogen bond, between layers, as
dashed lines.
Table 2
Distances (Å) and angles (°) of hydrogen bond for 1, 2, 3 and 4.
D–H…A
d(D–H)
d(H…A)
d(D–A)
D–H–A
Symmetry
Compound 1
N(3)–H(3N)…Cl(1)
N(4)–H(4N)… Cl(2)
C(10)–H(10)… Cl(2)
C(16)–H(11a)…S(1)
Compound 2
0.86
0.86
0.93
0.97
2.78
2.37
2.76
2.86
3.527(5)
3.204(5)
3.506(5)
3.654(5)
146
163
138
139
x,1/2-y,-1/2+z
1-x,-1/2+y,3/2-z
x, y, z
–1+x, y, z
N(3)–H(3N)…Cl(2)
N(4)–H(4N)… Cl(1)
C(3)–H(3)… Cl(2)
Compound 3
0.86
0.86
0.93
2.37
2.77
2.74
3.204(2)
3.523(1)
3.492(3)
163
147
138
2-x,-1/2+y,3/2-z
x,1/2-y,-1/2+z
x, y, z
N(4a)–H(4aN)…Cl(1b)
N(3b)–H(3bN)…Cl(2a)
N(3a)–H(3aN)…Cl(1b)
N(4a)–H(4aN)…Cl(2b)
0.86
0.86
0.86
0.86
2.63
2.37
2.81
2.82
3.280(3)
3.211(3)
3.372(3)
3.281(3)
133
164
125
115
-x,-1/2+y,1-z
-x,1/2+y,2-z
x,-1+y,z
1
+x,-1+y,z

N(4b)–H(4bN)…Cl(1a)
Compound 4
0.86
2.45
3.238(3)
152
-x,-1/2+y,1-z
N(4a)–H(4aN)…Cl(1b)
N(4b)–H(4bN)…Cl(1a)
N(3b)–H(3bN)…Cl(1a)
N(3a)–H(3aN)…Cl(2b)
0.86
0.86
0.86
0.86
2.48
2.81
2.62
2.39
3.266(8)
3.388(9)
3.283(8)
3.220(8)
152
126
135
163
x, y, z
x, y, z
1
-x,1/2+y,2-z
1-x,-1/2+y,1-z
Table 3
Intermolecular and intramolecular interactions C–H…Cg (C–H…π; Å, º) operating in the
crystal structure of 1, 2, 3 and 4 (Å, °).
C–H…Cg
d(C–H)
d(H…Cg) d(C–Cg)
C–H–Cg
Symmetry
Compound 1
C(12)–H(12)…Cg1 (N(1)/C(1)/N(3)/C(7)/C(2))
0.93
2.96
2.97
3.660(6)
3.671(3)
133
-1/2+x,y,3/2-z
1/2+x,y,3/2-z
Compound 2
C(5)–H(5)…Cg2 (N(2)/C(8)/ N(4)/C(14)/ C(9))
0.93
133
Compound 3
-
-
-
C(5b)–H(52)…Cg3 (N(2a)/C(8a)/N(4a)/C(14a)/C(9a))
C(151)–H(91b)…Cg4 (C(2a)/C(3a)/C(4a)/C(5a)/C(6a)/C(7a))
C(171)–H(92a)…Cg5
0.93
0.97
2.97
2.62
3.332(4)
3.346(7)
105
132
-1+x,y,z
-1+x,1+y,z
0
.97
0.97
.97
2.94
2.60
2.69
3.644(7)
3.253(13)
3.640(7)
130
125
168
1+x,-1+y,z
x,1+y,z
(
C(9b)/C(10b)/C(11b)/C(12b)/C(13b)/C(14b))
-
C(152)–H(91d)…Cg4 (C(2a)/C(3a)/C(4a)/C(5a)/C(6a)/C(7a))
-
C(172)–H(92b)…Cg5
0
x,-1+y,z
(
C(9b)/C(10b)/C(11b)/C(12b)/C(13b)/C(14b))
Compound 4
-
-
/
C(5a)–H(5a)…Cg6 (N(1b)/C(1b)/ N(3b)/C(7b)/ C(2b))
C(15a)–H(15b)…Cg7 (C(9b)/C(10b)/ C(11b)/C(12b)/ C(13b)
C(14b))
0.93
2.90
2.80
3.376(15)
3.388(8)
113
120
1+x,-1+y,z
1+x,y,z
0
0
.97
.97
-
C(15b)–H(15c)…Cg8 (C(9a)/C(10a)/ C(11a)/C(12a)/ C(13a) /
2.97
3.664(9)
128
-1+x,y,z
C(14b))
Computational investigation
In order to provide a better understanding of the bonding and the electronic structure of the
Co(bbms)Cl } (1), {Zn(bbms)Cl } (2), {Co(btmb)Cl } (3) and {Zn(btmb)Cl } (4)
{
2
2
2
2
complexes, we have carried out DFT calculations. Calculations have been performed without
any symmetry constraints on the neutral and on the mono-reduced forms of 1 and 3 species
(
Figures 6 and 7), but only on the neutral of 2 and 4 ones. Selected computed data for the
obtained structures are given in Tables 4. Full geometry optimizations of 1 and 3 show that
the Co(II) metal cation is in a tetrahedral environment as an ML complexes having a 15-
MVE (metal valence electrons) configuration. Indeed, the average Co-N bond distances of
4

2
.042 and 2.028 Å and the average Co-Cl bond distances of 2.242 and 2.250 Å, obtained for 1
and 3, respectively, are comparable to those obtained experimentally (Table 4). The N-Co-N
bond angles of 110 and 112° computed for 1 and 3 complexes, respectively, are close to the
experimental ones of 109°, while the calculated Cl-Co-Cl of 132 and 128° are larger than the
experimental ones. The spin density values of 0.95 and 0.95 obtained for 1 and 3 show the
7
localisation of the unpaired electron on the Co(II) center as d metal in both cases. The singly
occupied molecular orbital 68a (SOMO) is mainly metallic of (75% composed of dxy and dyz
and 65a (57% composed of d ) for 1 and 3, respectively, as displayed in Figure 7 showing
that the reduction will occur on the metal and will affect its oxidation state. We have
)
x y
2- 2
-
-
-
-
optimized the geometries of the 1 and 3 models in their singlet (1 (S) and 3 (S)) and triplet
-
-
-
-
(
1 (T) and 3 (T)) sates corresponding to Co(I) center. Indeed, the reduced 1 and 3 species in
-1
their triplet state are more stable than the single ones by 22.4 and 9.4 kcal mol , respectively.
Indeed, the one electron reduction decreases the oxidation state and the cobalt center becomes
8
7
-
-
Co(I) d center instead of Co(II) d one. The structures of the reduced 1 (S) and 3 (S) forms
(
Figure 7) exhibit moderate but significant HOMO-LUMO gaps of 0.61 and 1.06 eV (Figure
-
8
), respectively. Surprisingly, 1 (S) complex adopts different structure than the neutral one,
wherein the metal environment undergoes remarkable structural modification associated with
Cl-Co-Cl and N-Co-N bond angles opening of 163 and 148°, respectively, tending towards
the linearity, and thus giving rise to a quasi-square planar ML
4
geometry with a 16-MVE
configuration. Moreover, the NClNCl dihedral angle of 19° deviates slightly from the
-
-
planarity. Whereas for the 3 (S) and 3 (T) structures, one can observe a remarkably structural
modification corresponding to a C-S bond rupture of the (CH) -S bridge leading to positives
2
interactions between cobalt and sulphur atoms highlighted by a short Co-S distance of 2.556
-
Å for 3 (S) species.
Fig. 6. Optimized structures of complexes 1, 2, 3 and 4.

Fig. 7. Reduction mechanisms for neutral 1 (a) and 3 (b) complexes of 15-MVE giving rise to
singlet and triplet species of 16-MVE.
Table 4
Selected parameters obtained for neutral and reduced complexes. Experimental bond
distances are given in parentheses.
-
-
{
Co(bbms)Cl
2
}
{Co(bbms)Cl
2
}
{Co(btmb)Cl
S = 1/2
3
2
}
{Co(btmb)Cl
2
}
{Zn(bbms)Cl
2
}
2
{Zn(btmb)Cl }
S = 1/2
S = 0
-
1 (S)
S = 1
-
1 (T)
S = 0
S = 1
S = 0
2
S = 0
4
-
3 (S)
-
3 (T)
1
MVE
E (kcal mol )
15
16
16
0.0
-
15
16
16
0.0
-
18
18
-
1
∆
-
22.4
0.61
-
9.4
1.06
-
-
HOMO-LUMO gap (eV)
Average M-N(Å)
-
-
3.18
3.13
2.042
2.028
(2.009)
2.250
(2.251)
112
1
2
.907
.273
2.025
1.972
2.038
2.146
2.241
2.143
2.171
(
2.041)
2.242
2.253)
110
112)
132
109)
0.95
Average M-Cl (Å)
N-M-N (°)
2.303
106
2.294
164
2.263
115
(
148
104
(109)
127
(110)
-
97
(
(112)
128
(109)
125
(113)
-
Cl-M-Cl (°)
163
126
94
-
114
(
(109)
0.95
Spin density
-
2.19
2.08
2 2
Both {Zn(bbms)Cl } (2) and {Zn(btmb)Cl } (4) structures exhibit large HOMO-LUMO gaps
of 3.18 and 3.13 eV, respectively, satisfying the 18-electron configuration and synonymous of
good kinetic and thermodynamic stabilities. The optimized average Zn-Cl and Zn-N bond

distances of 2.241 and 2.146 Å, respectively, obtained for 2 are comparable to those obtained
for 4 of 2.171 and 2.143 Å, respectively, and comparable to the experimental values (Table
4
), while the Cl-Zn-Cl and N-Zn-N bond angles of 127 and 104° obtained for 2 are slightly
less open than those obtained for 4 of 125 and 97°, respectively, in accordance with the long
and short (CH S and (CH )S bridge in 2 and 4 complexes, respectively. However, 2 and 4
are considered as tetrahedral ML complexes in consideration of bond angles comparable to
2
)
2
2
4
1
0
those obtained experimentally corresponding to Zn(II) as d metal. For both 2 and 4
complexes, it is worth noting that the three highest occupied MOs are purely chlorine
exhibiting neglected metal contributions do not exceed 2%, thus, oxidations and reductions of
2
and 4 will not affect Zn metal and its environment. Noticing that the purely metallic MOs
are situated at low energies ranging from -10.86 to -10.52 eV, while the HOMO, HOMO-1
and HOMO-2 which are chlorine orbitals ranging from -5.73 to -5.62 eV.
-
Fig. 8. MO diagrams for neutral 1 and 3 and anionic 3 and 3 (S) species. LUMO energies are
set arbitrary to zero for comparison facilities.
Corrosion test
The prepared complexes were subjected to two types of electrochemical measurements in
order to evaluate and confirm their abilities to inhibit the corrosion of steel in aqueous acid
solutions.
Polarization Measurements
The potentiodynamic polarization curves (Tafel curves) for steel in 0.5 M H
2
SO in absence
4
-3
and presence of 5×10 M of compounds 1, 2, 3 and 4 are shown in Figure 9.

-
3
Fig. 9. Polarization curves of steel in 0.5 M H
2
SO without and with 5×10 M of compounds
4
1
-4 at 298 K.
It is clear from Figure 9 that the presence of all inhibitors causes a decrease in the corrosion
rate i.e., shifts both anodic and cathodic curves to lower current densities. At the same time,
this change is associated with a negative shift in Ecorr compared with that of the blank solution
(
not more than 45 mV versus SCE). The results suggest that all compounds act as mixed-type
inhibitors for steel in 0.5 M H SO solution [60,61].
2
4
It should be noted that the cathodic current–potential curves give rise to parallel Tafel lines in
the presence and in the absence of the tested compounds. This indicates that the adsorbed
6
2
inhibitors do not affect the mechanism of hydrogen evolution. Furthermore, It should be
noted that no change in the anodic Tafel slopes are observed in presence of compounds 2 and
4
. However, a slight changes were observed in the case of 1 and 3, suggests that all
compounds doesn’t affect considerably the dissolution mechanism of steel.
The corrosion parameters such as corrosion current density (Icorr), corrosion potential (Ecorr),
Tafel slopes (ba and bc), surface coverage θ and inhibition efficiency (IE %) are given in
Table 5. The surface coverage θ values and the inhibition efficiency were determined from the
equation 1 and 2 respectively [60]:
ꢂꢆꢇꢈꢈꢄꢉꢅ − ꢂꢆꢇꢈꢈ
ꢂꢃꢄ%ꢅ =
× 100ꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢄ1ꢅ
ꢂꢆꢇꢈꢈꢄꢉꢅ
ꢂꢌꢍꢎꢎ
ꢋ = 1 −
ꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢄ2ꢅ
ꢂꢌꢍꢎꢎꢄꢏꢅ

The values of the corrosion current density (Icorr) and the corrosion potential (Ecorr) were
obtained from the intersection of the anodic and cathodic curves through extrapolation of the
Tafel line, where Icorr and Icorr(0) are the corrosion current density with and without inhibitor in
the 0.5 M H
As shown in Table 5, the result shows that all compounds inhibit the corrosion of steel in 0.5
M H SO solution and the inhibitive ability increase when btmb was used instead of bsbm. In
2 4
SO solutions, respectively.
2
4
addition, the nature of metal doesn’t have a significant effect in inhibition efficiency. The
inhibition efficiency for 3 and 4 were 91.3% and 88.6%, respectively, which is higher than
-3
that obtained for 1 (86.5%) and 2 (86.7%) at the same concentration (5×10 M).
Table 5
-3
Polarization parameters and IE% for steel corrosion in 0.5 M H
2
SO
4
without and with 5×10
M of inhibitors 1-4 at 298 K.
-
1
-1
E
corr
I
corr
ba (mV. dec ) bc (mV. dec ) IE %
-2
(
mV)
(µA.cm )
235.1
31.9
Blank
-485
97.4
77.9
83.6
113.7
98.2
135
-
{Co(bbms)Cl
{Zn(bbms)Cl
{Co(btmb)Cl
{Zn(btmb)Cl
2
} (1) -494
113.2
107.1
119.2
115.8
86.5
86.7
91.3
88.6
2
} (2) -504
} (3) -509
} (4) -504
31.0
2
20.1
2
26.6
Electrochemical impedance spectroscopy measurements
EIS was also used to investigate the adsorption process by calculating the double layer
capacitance (Cdl) and the charge transfer resistances (Rct) under different conditions [63-65].
Figure 10 shows the Nyquist diagrams for steel in 0.5 M H SO in the presence and absence
of compounds 1-4.
2
4

-
3
Fig. 10. Nyquist plots for steel in 0.5 M H
2
SO solutions without and with 5×10 M of
4
compounds 1-4 at 298 K.
The impedance spectra in absence and presence of all compounds exhibit a single depressed
capacitive loop. Clearly, the capacitive loops in the presence of all compounds are larger than
that in the absence of inhibitors (blank solution), which proves that corrosion resistance of
steel occurs in presence of these compounds. Furthermore, the diameters of the capacitive
loops in the presence of inhibitor 3 and 4 are larger to those obtained in the presence of
inhibitor 1 and 2 (Figure 10).
The electrochemical parameters derived from the Nyquist diagram are given in Table 6. The
R
s
represent the resistance of solution. Double-layer capacitance (Cdl) values were calculated
using the following equation (3) [66-68].
ꢄꢁꢖꢗꢅ ꢁꢘ
ꢀꢐꢑ = ꢄꢒ × ꢓ
ꢅ
ꢗꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢄ3ꢅ
ꢉ
ꢔꢕ
Y
0
and n are the magnitude of admittance of the constant phase element (CPE) and the
electrode surface roughness/heterogeneity factor, respectively.
0
Analyze of the impedance results in Table 6 shows that the values of Cdl and Y are smaller in
the presence of all compounds than in their absence. Complementarily, the values of Rct
increase in presence of all compounds. These results suggest that all compounds formed a
protective layer on the electrode surface and act as a barrier for charge transfer [69,70].
In other hand, the values of the phase shift n decrease in presence of all compounds, when
compared to that obtained in 0.5M H
2
SO (0.8898). This shows an increase of the surface
4
inhomogeneity as a result of the inhibitor’s adsorption [71].

The inhibition efficiencies for all compounds were calculated using the following equation
4):
(
ꢓꢆꢙ − ꢓ
ꢆꢙꢄꢉꢅ
ꢂꢃꢄ%ꢅ =
× 100ꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢊꢄ4ꢅ
ꢓꢆꢙ
where Rct(0) and Rct are charge transfer resistance in the absence and presence of inhibitor
respectively.
From Table 6, the EIS measurements also shows that the all compounds can clearly inhibit the
2 4
corrosion of steel in 0.5 M H SO solution and the inhibition efficiency of the investigated
inhibitors increases in the following order: 3 and 4 > 1 and 2. This result is in a good
agreement with this obtained from potentiodynamic polarization measurements (Table 5).
Table 6
Impedance parameters and inhibition efficiency for steel in 0.5 M H
2
4
SO without and with
-3
5
×10 M of inhibitors 1-4 at 298 K.
2
2
R
s
(Ω.cm ) Rct (Ω.cm ) n
Y
0
C
dl
IE %
n
-2
-
-2
(
S .cm . Ω ) (μF.cm )
Blank
2.606
89.55
543.7
554.1
798.1
848.7
0.8898 152.2
0.8038 55.9
0.7803 130.2
0.8387 46.1
0.7554 103.0
89.4
23.8
62.1
24.42
46.7
-
{Co(bbms)Cl
{Zn(bbms)Cl
{Co(btmb)Cl
{Zn(btmb)Cl
2
} (1) 1.430
83.5
83.8
88.8
89.4
2
} (2) 2.139
} (3) 1.562
} (4) 1.357
2
2
Antimicrobial assays
The present method used to evaluate the antimicrobial activity of the prepared complexes was
carried out by replacement the paper disc, used in standard method [72], with a solid tablet of
the test compound adsorbed onto an adsorbing agent (peptone). This modification was
introduced as a result of the low water solubility of the tested compounds which reduce their
diffusion on the agar plate. The results of the antimicrobial screening of the prepared
compounds are summarized in Table 7.
The comparison of inhibition zone diameters revealed that the majority of the tested
complexes were found to have moderate to good antimicrobial activities against
Staphylococcus aureus, Pichia caribbica and Pseudomonas syringae and are more efficient
vs. this latter compared with the standard drug. However, in all case, no activity was observed
against Klebsiella pneumonia.

Furthermore, in most case, the comparison of antimicrobial activities of the complexes with
theirs corresponding ligands show that the presence of metal in the molecule skeleton increase
the antibacterial activity against Pseudomonas syringae, Staphylococcus aureus and Pichia
caribbica. However, the nature of metal or the ligand type doesn’t have a significant effect in
inhibition zone diameters.
Table 7
In Vitro Antibacterial activity of ligands bbms, btmb and complexes 1-4.
Inhibition zones in mm
Ps
16
15
20
22
12
12
0
Sa
27
30
27
15
0
Kp
0
Pc
25
18
22
0
{
{
{
{
Co(bbms)Cl
Zn(bbms)Cl
Co(btmb)Cl
Zn(btmb)Cl
2
} (1)
2
} (2)
0
2
} (3)
0
2
} (4)
0
Btmb
Bbms
0
0
0
0
0
benzylpenicilline sodique
50
0
6
Ps: Pseudomonas syringae; Sa: Staphylococcus aureus; Kp: Klebsiella pneumonia; Pc: Pichia caribbica.
Conclusion
In summary, four coordination metal complexes were synthesized by simple method.
Single crystal X-Ray diffraction analysis of all complexes reveals their monomeric tetra-
coordinated nature. The coordination polyhedron around the metal center may be described as
a quasi-regular tetragonal geometry. The results of corrosion inhibition efficiency evaluation
show that the prepared complexes can be effectively used as corrosion inhibitors for steel in
acid medium. The order of the inhibition efficiency of the complexes as given by polarization
measurements is in good agreement with that obtained from electrochemical impedance
measurements. Potentiostatic polarization data indicated that these compounds are mixed-type
inhibitors. In other hand, all complexes were evaluated for their in vitro antimicrobial activity
against Pseudomonas syringae, Staphylococcus aureus, Klebsiella pneumonia and Pichia
caribbica. In most cases, the prepared complexes have shown moderate to significant
antimicrobial activities against Staphylococcus aureus, Pichia caribbica and Pseudomonas
syringae. DFT/BP86 calculations carried out on neutral 1-4 complexes showed similarities
between optimized models and experimental structures. Moreover, a careful analysis of their

electronic structures indicated almost identical characteristics of neutral Co(II) on one hand
and the Zn(II) on other hand, but the reduced Co(I) forms behave differently in accordance
2 n
with the (CH ) S bridge length and adopting different structures than those of the neutral ones
and allowing a flexibility to the metal coordination sphere.
Acknowledgements
This work was supported by Mentouri Brothers University (Algeria). The authors thank
MESRS and DGRST for financial support. A. Bouraiou thanks Dr. Sara Mahdjoub for his
technical assistance in biological evaluation.
Appendix
Supplementary data CCDC 1432478–1432481 contains the supplementary
crystallographic data for {Co(bbms)Cl
2
}, {Co(btmb)Cl
2
}, {Zn(bbms)Cl
2
} and
{
Zn(btmb)Cl }, respectively. These data can be obtained free of charge via http://
2
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. Supplementary data associated with this article can be found, in the
online version, at http://dx.doi.org/10.1016/j.poly..........................
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Graphical abstract
Synopsis
Synthesis, characterization and DFT analysis of {Co(bbms)Cl
Co(btmb)Cl } and {Zn(btmb)Cl } containing benzimidazole thioether have been described.
2
2
}, {Zn(bbms)Cl },
{
2
2
These later show the corrosion inhibition ability of the prepared complexes for steel in acid
medium. Furthermore, these complexes show moderate to significant antimicrobial activities.
DFT/BP86 calculations have been carried out.