Spectral characterization and antimicrobial activity of 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols and their zinc(II) complexes

Article abstract of DOI:10.1016/j.saa.2010.05.008

2-(5-Chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols (HL _x; x = 1-4) and their complexes with zinc(II)nitrate have been synthesized and characterized. In the tetrahedral mononuclear complexes, the ligands are bidentate, via the imine n

Full text of DOI:10.1016/j.saa.2010.05.008

Spectrochimica Acta Part A 77 (2010) 199–206
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectral characterization and antimicrobial activity of
2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols and their
zinc(II) complexes
Aydin Tavmana,∗, Ismail Bozb, A. Seher Birteksözc
a Istanbul University, Faculty of Engineering, Department of Chemistry, 34320, Avcılar, Istanbul, Turkey
b Istanbul University, Faculty of Engineering, Department of Chemical Engineering, 34320, Avcılar, Istanbul, Turkey
c Istanbul University, Faculty of Pharmacy, Department of Pharmaceutical Microbiology, 34452, Beyazit, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
2-(5-Chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols (HLx; x = 1–4) and their complexes
with zinc(II)nitrate have been synthesized and characterized. In the tetrahedral mononuclear complexes,
the ligands are bidentate, via the imine nitrogen and the phenolate oxygen atoms. The structures of the
complexes were confirmed on the basis of elemental analysis, molar conductivity, TGA, FT-IR, NMR, mass
and UV–vis spectroscopy. The optimized geometry of the complexes was derived from theoretical cal-
culation in DGauss/DFT level on CACHE program. From theoretical calculations it was found that bromo
derivatives of the ligands (HL1 and HL3) have higher stability than the other ligands and similarly, their
Zn(II) complexes have higher stability than the other complexes. The antimicrobial activities of the com-
pounds were evaluated using the disk diffusion method against six bacteria and Candida albicans. All of the
complexes exhibited selective antibacterial activity on Staphylococcus epidermidis. HL3 and [Zn(L1)2]·H2O
are more active than Ciprofloxazin and, [Zn(L2)2] has antibacterial activity as potent as Ciprofloxazin
against S. epidermidis.
Received 9 October 2009
Received in revised form 4 May 2010
Accepted 15 May 2010
Keywords:
Chloro/nitro-benzimidazole
Bromo/nitro-phenols
Zinc(II) complexes
Antimicrobial activity
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
which can be activated by ionization, by polarization, or be poised
for displacement by a substrate. The most known enzymes con-
Benzimidazole derivatives display a wide range of biolog-
ical and pharmacological activity. For instance, vitamin B12
has 5,6-dimethylbenzimidazole moiety as coordinated to the
cobalt atom [1,2]. On the other hand, various drugs and
pharmaceutical compositions contain benzimidazole derivatives.
The perhaps most important one is an antisecretory agent,
omeprazole [5-methoxy-2-(4-methoxy-3,5-dimethylpyridin-2-yl-
methylsulfinyl)-1H-benzimidazole] [3]. The other important ben-
zimidazol derivatives, which are used as drugs, are thiabendazole
[4,5], albendazole, mebendazole, flubendazole [6,7] astemizole [8]
and fenbendazole [9]. In our previous studies, we found that various
benzimidazolyl-phenol derivatives showed antimicrobial activity
against several microorganisms [10–15].
taining zinc ion are carbonic anhydrase, carboxypeptidase, alcohol
dehydrogenase, thermolysin and ␤-lactamase. Zn(II) ion plays a
role in binding the water molecules and hydroxyl ions, and cat-
alyzes the hydration/dehydration mechanisms in the enzymes
[16].
Various biological activities of many Zn(II) complexes were
investigated. For example, Zn(II) complexes of 1,2-bis-[(5-
Cl/NO2)-2-1H-benzimidazolyl]-1,2-ethanediols were effective on
Staphylococcus aureus and Staphylococcus epidermidis [17]. Zn(II)
complexes of some 2-pyridinyl-1H-benzimidazoles showed selec-
tive antimicrobial effect against S. aureus and S. flexneri although
the ligands themselves had no effect [18]. Antibacterial activity
of 1-benzylbenzimidazole derivatives and their Zn(II) complexes
was evaluated. It was found that all the tested compounds were
more active against Gram-positive bacteria as compared to activi-
ties against Gram-negative bacteria [19]. Antimicrobial activity of
Zn(II), Ni(II), Cu(II) and Co(II) complexes of thiabendazole against
Escherichia coli, B. subtilis and A. flavues organisms was estimated.
The relationship between the enzymatic production of reactive
oxygen species (ROS) and antimicrobial activity of the complexes
was examined, and a good correlation between two factors was
found [5].
Zinc is an essential element and exists in multitudes of enzymes
and serves many vital biological roles in the biochemical systems.
It plays an active catalytic role and acts in regulatory or structural
roles. The unique feature of all structurally active mononuclear
zinc sites is the presence of a water molecule in the structure,
∗
Corresponding author. Tel.: +90 212 473 70 70; fax: +90 212 473 70 79.
E-mail address: atavman@istanbul.edu.tr (A. Tavman).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.05.008

200
A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
2.2. Synthesis of the ligands: general procedure
The ligands were prepared according to the literature
procedures [24,25]. For instance, 2-(5-chloro-1H-benzimidazol-2-
yl)-4-nitro-phenol (HL2) was obtained by reaction of 2-hydroxy-5-
nitrobenzaldehyde (1.67 g, 10 mmol) with an equivalent amount
of NaHSO3 (1.04 g, 10 mmol) at room temperature in 25 ml
ethanol for 4–5 h. The mixture was treated with 4-chloro-1,2-
phenylenediamine (1.42 g, 10 mmol) in 15 ml dimethylformamide
and gently refluxed for 2 h. The reaction mixture was then poured
into 500 ml icy water, filtered and crystallized from ethanol. This
method was selected because of its ease, high yields and shorter
synthesis time. This intermediate compound (namely, bisulfite
compound of the aldehyde) was utilized to catalyze the benzim-
idazole synthesis since 1,2-phenylenediamines and aldehydes do
not give cyclization reaction by themselves under mild conditions
and possibly might lead to Schiff bases.
Fig. 1. The structure of the ligands: R1 = Cl, R2 = Br, HL1; R1 = Cl, R2 = NO2, HL2;
R1 = NO2, R2 = Br, HL3; R1 = NO2, R2 = NO2, HL4.
Antibacterial activity of pyridine-3,5-bis(benzimidazole-2-yl)
and its Zn(II) complex was investigated and a selective inhibi-
tion property was observed for the tested strains [20]. Lukevics et
al. studied antitumor activity of trimethylsilylpropyl substituted
benzimidazoles and their ZnCl2, CuCl2, CoCl2, PdCl2 and AgNO3
complexes and they found that cytotoxicity of benzimidazole metal
complexes strongly depended on the nature of metal [21]. Antimi-
crobial activity of Zn(II), Fe(III), Cd(II) and Hg(II) complexes with
2,6-bis(benzimidazol-2-yl)pyridine was also studied and it was
found that M(L)Cl2 (M = Zn, Hg) complexes were exceptionally
effective in comparison to most of the reference antibiotics on bac-
teria and fungi [22]. Antibacterial and antifungal activity of Zn(II),
Co(II), Ni(II), Cd(II) complexes of pyridazinone was evaluated and
found that the complexes had considerable antimicrobial activity
[23].
In this work, 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-
bromo/nitro-phenols ligands (Fig. 1) and their zinc(II) nitrate
complexes were studied. This study is a part of a continuing project
on benzimidazoles. Our aim is to characterize and study the effect
of electron withdrawing substituent’s on benzimidazolyl-phenol
derivatives and their Zn(II) complexes. We also aim to investigate
antimicrobial activity of the ligands and the complexes against six
bacteria and Candida albicans as yeast. Herein, we also discuss the
differences of metal ion complexes with the free ligands in their
structural–biological activity relationship.
2.3. Synthesis of the complexes
[Zn(L4)2]·2H2O: HL4 ligand (150 mg, 0.5 mmol) was suspended
in 10 ml ethyl acetate. Zn(NO3)2·6H2O (190 mg, >0.5 mmol) solu-
tion in 15 ml ethyl acetate was added to the ligand solution. After
2 h of reflux, the dark green precipitate was filtered, washed with
5 ml of ethyl acetate and dried at 70 ◦C.
The other complexes were prepared in a similar manner to com-
plex [Zn(L4)2]·2H2O and the results are presented in Table 1.
2.4. Determination of antimicrobial activity
Antimicrobial activity against S. aureus ATCC 6538, S. epidermidis
ATCC 12228, E. coli ATCC 8739, Klebsiella pneumoniae ATCC 4352,
Pseudomonas aeruginosa ATCC 27853, Proteus mirabilis ATCC 14153
and Candida albicans ATCC 10231 were determined by the micro-
broth dilutions technique strictly following the recommendations
of National Committee for Clinical Laboratory Standards (NCCLS)
[26,27]. Mueller-Hinton broth for bacteria, RPMI-1640 medium
buffered to pH 7.0 with MOPS for yeast strain was used as the
test medium. Serial twofold dilutions ranging from 5000 ␮g/ml
to 4.9 ␮g/ml were prepared in medium. The inoculum was pre-
pared using a 4–6 h broth culture of each bacteria and 24 culture
of yeast strains adjusted to a turbidity equivalent to a 0.5 McFar-
land standard, diluted in broth media to give a final concentration
of 5 × 105 cfu/ml for bacteria and 0.5 × 103 to 2.5 × 103 cfu/ml for
yeast in the test tray. The trays were covered and placed in plastic
bags to prevent evaporation. The trays containing Mueller-Hinton
broth were incubated at 35 ◦C for 18–20 h and the trays containing
RPMI-1640 medium were incubated at 35 ◦C for 46–50 h. The min-
imum inhibitory concentrations (MIC) were defined as the lowest
concentration of compound giving complete inhibition of visible
growth. Antimicrobial effects of the solvents were investigated
against test microorganisms.
2. Experimental
2.1. Chemistry and apparatus
All chemicals and solvents are of reagent grade and were used
without further purification.
Elemental analysis data were obtained with a Thermo Finnigan
Flash EA 1112 analyzer. Decomposition points were determined
using an Electro thermal melting-point apparatus. Molar con-
ductivity of the complexes was measured on a WTW Cond315i
conductivity meter in DMSO at 25 ◦C. 1H and 13C NMR spectra were
run on a Varian Unity Inova 500 NMR spectrometer. The resid-
ual DMSO-d6 signal was also used as an internal reference. FT-IR
spectra were recorded in KBr disks on a Nicolet 380 FT-IR spec-
trometer. UV–vis spectra was performed on a Perkin Elmer Lambda
25 UV/visible spectrometer. The Electron Spray Ionization-Mass
Spectroscopy (ESI-MS) analyses were carried out in positive ion
modes using a Thermo Finnigan LCQ Advantage MAX LC/MS/MS.
Thermo gravimetric (TG) studies were made on a TG-60WS Shi-
madzu, with a heating rate of 10 ◦C/min under flowing air at the
rate of 50 ml/min.
2.5. Theoretical calculation
The structure of the complexes (shown in Fig. 7) was refined by
performing a geometry optimization routine in DGauss/DFT (den-
sity functional theory) available on CACHE work system pro version
6.1.10 package program. The B88-PW91 with the DZVP basis set
correlation functional of the generalized gradient approximation
(GGA) was used in calculations. The lowest energy values obtained
by using the DFT calculations are: HL1 (−3696), HL2 (−1344), HL3
(−3441), HL4 (−1073), Zn(L1)2 (−9205), Zn(L2)2 (−4468), Zn(L3)2
(−8697) and Zn(L4)2 (−3958); values inside parameters were in a.u.

A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
201
Fig. 2. The intramolecular hydrogen bonding in the ligands.
3. Results and discussions
The analytical and physical properties of the ligands and the
complexes are summarized in Table 1.
The high decomposition point of the ligands (between 277 and
328 ◦C) and especially of the chelate complexes (>350 ◦C) is an evi-
dence of that these compounds have high thermal stability. Molar
conductivity of the complexes in DMSO showed that all complexes
are non-electrolytes (Table 1).
Fig. 3. FT-IR spectra of HL1 and [Zn(L1)2]·H2O in the mid-IR region.
[31]. Slight but specific differences between spectra of the free lig-
ands and the complexes in this region lead to the conclusion of the
formation of new complexes.
3.1. IR spectra
In the IR spectra of HL2, HL3, HL4 ligands and their complexes,
the strong or medium bands near 1500 cm−1 (1532–1483 cm−1
)
FT-IR spectral data of the ligands and the complexes are given
in Table 2. The characteristic ꢀ(O–H) and ꢀ(N–H) vibration fre-
quencies of the ligands exhibit only a single strong band at ca.
3300 cm−1 in the IR spectra, caused by intramolecular hydrogen
bonding between the phenoxyl hydrogen atom and C N nitrogen
atom (Table 2 and Fig. 2) [15,28–30].
Appearance of a medium broad bands between 3444 and
3523 cm−1 in the Zn(II) complexes of HL1, HL3 and HL4 ligands
strongly support the idea of the presence of water molecule(s). The
N–H stretching vibrations of the ligands are observed at wavenum-
bers between 3227 and 3373 cm−1 in the complexes, suggesting
that the amine proton remained attached at the N-1 (NH) position
(Fig. 1).
The characteristic ꢀ(C–H) and ı(C–H) modes of aromatic rings
in the ligands and the complexes are observed at 3125–3072 and
850–720 cm−1 (Table 2 and Fig. 3) regions, respectively [15]. The
benzene C C and the imidazole C N stretching frequencies are
expected to appear at between 1630 and 1590 cm−1 with their own
characteristics for the ligands and the complexes in the IR spectra
and at the 1377–1305 cm−1 range are assigned to the symmetric
and asymmetric ꢀ(NO2), respectively [31].
The C–Br stretching vibration is seen at 550, 515, 554 and
541 cm−1 as medium bands for HL1, Zn(L1)2, HL3, Zn(L3)2, respec-
tively [32]. The C–Cl stretching vibration is observed at 634, 608,
649 and 641 cm−1 as medium or weak bands for HL1, Zn(L1)2, HL2,
Zn(L2)2, respectively [33].
3.2. UV–vis spectra
The UV–vis spectral data are presented in Table 2. The UV–vis
spectra of the ligands and the complexes in methanol showed
three to five absorption bands. The lower wavelength bands
(200–300 nm) correspond to ␲ → ␲* transition of the aromatic
rings. The bands between 300 and 350 nm are due to n → ␲* tran-
sitions. The visible region (>350 nm) bands in the Zn(II) complexes
are due to L → Zn (oxygen → zinc) charge transfer (reason of the
darker color of the complexes than the ligands) [34–36].
Table 1
The analytical and physical properties of the ligands and the complexes.
Compound
Elemental analysis Found (Calcd) (%)
Yield (%)
Dec. (◦C)
ꢁa
Color
C
H
N
HL1
C13H8BrClN2O
HL2
C13H8ClN3O3
HL3
48.4 (48.2)
2.8 (2.5)
8.6 (8.7)
64
63
58
70
74
80
73
63
309
328
–
–
Dirty white
Yellow
54.2 (53.9)
46.4 (46.7)
52.3 (52.0)
42.5 (42.9)
48.6 (48.6)
41.1 (40.7)
44.2 (44.6)
3.1 (2.8)
2.6 (2.4)
3.1 (2.7)
2.0 (2.2)
2.7 (2.2)
2.5 (2.4)
2.9 (2.6)
14.4 (14.5)
12.8 (12.6)
18.4 (18.7)
7.4 (7.7)
277
–
Dark yellow
Dark yellow
Dark yellow
Dark yellow
Light brown
Dark green
C13H8BrN3O3
HL4
318
–
C13H8N4O5
[Zn(L1)2]·H2O
>350
>350
>350
>350
8
C26H16Br2Cl2N4O3Zn
[Zn(L2)2]
12.6 (13.1)
11.4 (10.9)
16.5 (16.0)
13
15
21
C26H14Cl2N6O6Zn
[Zn(L3)2]·2H2O
C26H18Br2N6O8Zn
[Zn(L4)2]·2H2O
C26H18N8O12Zn
a
ꢁ, molar conductivity in DMSO, ꢂ−1 cm2 mol−1 (25 ◦C). Dec., decomposition.

202
A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
Table 2
FT-IR and UV–vis spectral data of the ligands and the complexes.
Compound
HL1
Frequency (cm−1), KBr pellets
Wavelength (nm), in MeOH
226, 246sh, 292, 300, 327, 341
3340s, 3072m, 2921m, 1632m, 1623m, 1580m, 1485s, 1377s, 1284m, 1255s, 1140m,
1062m, 843m, 812s, 634m, 577m, 550m, 424m
[Zn(L1)2]·H2O
HL2
3451m,br, 3296m, 3093m,br, 1625m, 1598m, 1515s, 1471s, 1351m, 1308m, 1255m,
1069m, 824m, 723m, 608m, 515m, 429m
3263s, 3097w, 1630m, 1608m, 1587s, 1488m, 1396m, 1338s, 1317s, 1296s, 1133s,
1062m, 937m, 807m, 748m, 649m, 573m
229sh, 254, 262, 268, 326, 344, 366br,
382, 437br
211, 228, 297, 320, 335, 356sh, 402br
[Zn(L2)2]
HL3
3279s, 3112m, 1624m, 1598m, 1561m, 1489s, 1346s, 1314s, 1135s, 1062m, 838m,
805m, 752m, 645m, 508w
3327m,br, 3085m, 1630m, 1597m, 1583m, 1518s, 1483s, 1339s, 1322s, 1249s, 1065m,
970m, 817m, 737m, 633m, 554m, 468w
223, 269, 297, 320, 334, 412br, 477br
214, 230, 263 269, 349
[Zn(L3)2]·2H2O
HL4
3460m,br, 3373m,br, 3104m, 1631m, 1604m, 1527m, 1515m, 1474m, 1345m, 1248m,
1144m, 1060m, 819m, 738m, 624m, 541m, 465w
3264m, 3100m, 1659m, 1631m, 1612m, 1592m, 1518m, 1483m, 1342s, 1329s, 1299s,
1129m, 891m, 812m, 736m, 643m, 569w, 468w
216, 226, 264 351, 498
228, 262, 269, 342, 413br
[Zn(L4)2]·2H2O
3523m,br, 3227m,br, 3123m, 1626m, 1610m, 1563m, 1532m, 1488s, 1350s, 1305s,
1135s, 1085m, 900m, 820m, 732m, 628m, 473w
230, 268, 299br, 337, 486br, 538br
3.3. NMR spectra
observed at 7.26 and 7.41 ppm, respectively. H6 proton appeared
at 6.91 ppm. Similarly, the NMR spectral studies of some 2-(2-
hydroxyphenyl)-1H-benzimidazole derivatives were also reported
[25,28,40].
1H NMR spectral data and their assignments are presented
in Table 3. 1H NMR spectra of HL2 and [Zn(L2)2] are pre-
sented in Fig. 4. The 1H NMR spectra of HL2 and HL4 ligands
exhibit only a single broad band for the OH and the amine NH
protons (13.81 and 13.61 ppm for HL2 and HL4, respectively).
This combination results from strong intramolecular hydrogen
bonding between the amine nitrogen with double bond and
phenolic hydrogen atoms (Fig. 2) [33,37]. In the HL3 spec-
tra two broad singlets are observed for these protons. The
NH and OH protons could not be detected in HL1 spectra
(Table 3).
It is observed that benzimidazole ring protons of HL1 and HL2
(having chloro substituent 5-position on the benzimidazole ring)
appear below 8.0 ppm (Fig. 4). Namely, 8.31 and 9.06 ppm sig-
nals must belong to the H3ꢀ proton in the spectra of HL1 and
HL2, respectively. The ppm values of H4 protons of HL1, HL2,
[Zn(L1)2]·H2O and [Zn(L2)2] are 7.73, 7.76, 7.91, 7.99, respec-
tively (Fig. 4). However, the protons neighboring to the nitro
group (HL2, HL3 and HL4) are observed at above 8.0 ppm. HL3
and HL4 have a nitro group at the 5-position on the benzim-
idazole ring. The chemical shift values of H4 protons of HL3,
HL4, [Zn(L3)2]·2H2O and [Zn(L4)2]·2H2O are 8.51, 8.60, 8.94,
9.00 ppm, respectively. It is known that the nitro group on aro-
matic ring moves the resonance of the ortho protons downfield
by approximately +0.95 ppm, while bromine and chlorine atoms
move them approximately +0.2 and 0.0 ppm, respectively [41].
In the literature, 1H NMR spectrum of benzimidazole was
reported firstly by Black and Heffernan (in CD3OD) [38]. They
reported that H4 (or H7) protons appeared at 7.61 ppm and H5 (or
H6) protons at 7.24 ppm. On the other hand, Claramunt et al. studied
the tautomerism of omeprazole in THF-d8 by means of NMR spec-
tra [39]. They reported that the signals of H4 and H7 protons were
Fig. 4. 1H NMR spectra of HL2 and [Zn(L2)2].

A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
203
Table 3
1H NMR spectral data (the chemical shift values, ıH, ppm, with coupling constants, J, Hz, in DMSO-d6).
Compound
The benzimidazole protons
The phenolic protons
H4
H6
H7
NH
H3ꢀ
H5ꢀ
H6ꢀ
OH
a
a
HL1
7.73 d
J = 1.9
7.91 d
J = 2.6
7.76 d
J = 2.0
7.99 s,br
7.33 d-d
J = 8.8, 1.9
8.07 d-d
J = 9.3, 2.7
7.31 d-d
J = 2.1, 8.8
8.09 s,br
7.69 d
J = 8.8
7.54 s,br
–
8.31 d
J = 2.4
8.26 s
7.53 d-d
J = 8.8, 2.4
7.28 s,br
7.07 d
J = 8.8
6.68 d,br
J = 9.1
7.20 d
J = 9.3
6.73 s,br
–
[Zn(L1)2]·H2O
HL2
13.53 s,br
13.81 s,br
13.65 s,br
13.41 s,br
13.44 s,br
13.61 s,br
–
7.69 d
J = 8.7
7.32 d,br
J = 10.4
7.78 d
9.06 d
J = 3.1
8.97 s,br
8.23 d-d
J = 9.1, 3.1
7.69 s,br
13.81 s,br
[Zn(L2)2]
HL3
–
8.51 s,br
8.14 d-d
J = 8.9, 1.5
7.82 s,br
8.29 d
J = 2.2
8.15 d,br
J = 2.4
9.13 d
J = 2.7
9.00 s,br
7.55 d-d
J = 8.8, 2.4
7.38 s,br
7.04 d
J = 8.9
6.83 s,br
12.37 s,br
J = 8.8
7.71 s,br
[Zn(L3)2]·2H2O 8.94 s
–
HL4
8.60 s,br
8.20 d-d
J = 1.8, 8.7
8.14 s,br
7.88 d
J = 8.7
7.81 d,br
J = 6.8
8.30 d-d
J = 2.7, 8.9
8.19 d-d
J = 8.8, 2.0
7.28 d
J = 8.9
6.96 s,br
13.61 s,br
–
a
[Zn(L4)2]·2H2O 9.00 s,br
–
a
Not detected.
Indeed, it is observed that the nitro groups move the resonance
of the ortho protons (H4, H6, H3ꢀ and H5ꢀ) downfield (above
8.0 ppm) in the 1H NMR spectra of HL4 and its Zn(II) com-
plex.
It is observed that the doublets and doublets of doublets at the
NMR spectra of the ligands which belong to the protons of the ben-
zimidazole benzene and phenol rings, changed to broad doublets
on complexation. It is interesting to note that H3ꢀ and H4 protons
in [Zn(L4)2]·2H2O complex show a broad singlet at almost the same
position, 9 ppm.
13C NMR spectral data are given in Table 4. In the 13C NMR spec-
tra of the ligands and the complexes the signals at the highest ppm
values (over 150 ppm), e.g. 157.6 and 150.6 ppm for HL1, belong
to C1ꢀ, bonded to the OH oxygen, and imidazole C N (C2) carbon
atoms, respectively [39]. NMR signals belonging to C8, C9 and also
the carbon atoms that bonded to the nitro group appear at the
140–150 ppm region. The other signals belong to the benzimidazole
Fig. 5. ESI-MS spectra of [Zn(L3)2]·2H2O.
of non-existence of coordinated and uncoordinated water molecule
[42–45] and, it is in line with the ESI-MS data and elemental analysis
of [Zn(L2)2] complex.
TGA curves showed that decomposing of the complexes start
above 350 ◦C except [Zn(L4)2]·2H2O. [Zn(L4)2]·2H2O starts to
decompose above 200 ◦C. On the other hand, it is observed that
a considerable weight loss occurred in this complex. This complex
contains two nitro groups and, it is assumed that weight loss is due
to the elimination of two nitro groups above 200 ◦C. This result is in
benzene and phenol rings carbon atoms (Table 4). Good quality 13
C
NMR spectra for [Zn(L2)2] and [Zn(L4)2]·2H2O complexes could not
be recorded because of their low solubility characters in DMSO-d6
and in the other strong solvents such as methanol and DMF, too.
3.4. Mass spectra
The ESI-MS spectral data of the complexes are given in Table 5
as molecular ions with the relative abundance. The assignments
of the some intense ions are given in Table 5, also. Molecular ions
of the complexes are observed in their ESI-MS spectra. The ions
for Zn(L3)2 and Zn(L4)2, [M−2H2O]+, are present at m/z values of
729.6 and 663.2, respectively (Fig. 5). Also, the peaks of the ligands
are easily determined in the mass spectra of the complexes (the
ligands are shown as L in Table 5).
The higher m/z values than the molecular ions may be due to
condensation products of lower mass ions. Some of the higher m/z
values according to the molecular ions can be interpreted as form-
ing of the polymeric structures under ESI-MS conditions.
3.5. Thermogravimetric analyses
The major features of the thermal analysis of the complexes are
summarized in Table 6. TGA curves of [Zn(L1)2]·H2O, [Zn(L2)2] and
[Zn(L4)2]·2H2O complexes are shown in Fig. 6.
In the TG analysis of [Zn(L2)2], there is no comparatively sig-
nificant weight loss until 300 ◦C. At about 300 ◦C, a weight loss of
3.1% is observed (Fig. 6). This finding alone is explained as a proof
Fig. 6. TGA curves of [Zn(L4)2]·2H2O (1), [Zn(L1)2]·H2O (2) and [Zn(L2)2] (3) com-
plexes.

204
A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
Table 4
13C NMR spectral data (in DMSO-d6).
Compound
Chemical shifts (ıC, ppm)
HL1
157.6, 150.6, 135.8, 130.2, 128.8, 124.7, 116.7, 115.1, 114.3, 111.1
161.0, 152.6, 144.8, 134.8, 129.8, 128.2, 126.6, 119.8, 100.7
164.1, 151.5, 140.4, 128.4, 127.9, 124.3, 124.0, 118.9, 113.6
153.2, 128.1, 128.7, 126.2, 117.1
160.0, 157.5, 143.8, 135.6, 134.6, 132.2, 130.3, 129.4, 120.2, 119.7, 115.4, 111.2, 110.9
157.4, 153.9, 143.9, 141.1, 137.1, 136.0, 130.3, 120.1, 119.4, 115.4, 114.6, 112.2. 111.2
163.7, 154.0, 144.0, 140.5, 128.4, 125.0, 119.4, 118.9, 114.2
143.8, 132.3, 129.4, 128.5, 119.9, 119.6, 110.0
[Zn(L1)2]·H2O
HL2
[Zn(L2)2]
HL3
[Zn(L3)2]·2H2O
HL4
[Zn(L4)2]·2H2O
Table 5
ESI-MS spectral data of the complexes.
Compound and MW (g/mol)
Molecular ions (m/z) with relative abundance (%) and assignmentsa
[Zn(L1)2]·H2O 728.5
[Zn(L2)2] 642.7
[Zn(L3)2]·2H2O 767.6
732.5 (23.6, [MH4]+), 424.6 (15.3, [L+Zn+2H2O]+), 387.8 (12.5, [L+Zn]+), 368.3 (25.9, [(L+Zn)−OH−3H]+), 322.9 (100, L)
641.3 (26.9, [M−1]+), 550.0 (19.5, [M−2NO2]+), 352.1 (12.3, [M−L−1]+), 289.6 (100, L)
766.7 (100, [M−H]+), 768.7 (83.5, [M+1]+), 729.6 (33.2, [M−2H−2H2O]+), 666.8 (34.9, 2L), 434.5 (10.5, [L+Zn+2H2O]+), 396.9
(27.5, [L+Zn]+), 334.2 (25.5, L)
[Zn(L4)2]·2H2O 699.9
697.4 (9.3, [M−2H]+), 682.1 (7.0, [M−H2O]+), 663.2 (100, [M−2H2O]+), 597.8 (7.2, 2L), 410.2 (50.5), 298.9 (32.5, L)
a
The ligands are shown as L.
Table 6
TGA data of the complexes (thermal decompositions).
Complex
Temperature (◦C)
110
150
200
250
300
350
400
Weight loss (%)
[Zn(L1)2]·H2O
[Zn(L2)2]
3.4
0.8
5.2
4.5
3.8
1.2
7.1
6.9
4.2
1.9
7.3
5.5
2.3
8.4
7.6
3.1
11.3
19.1
9.8
3.9
15.4
25.2
16.7
4.6
51.0
73.2
[Zn(L3)2]·2H2O
[Zn(L4)2]·2H2O
10.8
15.8
agreement with the theoretical calculations. According to the the-
oretical calculations [Zn(L4)2]·2H2O has the lowest stability among
the complexes (see Section 3.7).
In the TG analysis of [Zn(L4)2]·2H2O complex, a weight loss is
observed for 4.5% ratio at ca. 100 ◦C (Fig. 6). This figure corresponds
to two moles of uncoordinated lattice water molecules [46,47]. The-
oretical weight loss for two moles of water is 5.1%. [Zn(L1)2]·H2O
and [Zn(L3)2]·2H2O complexes have similar TG curves to that of
[Zn(L4)2]·2H2O. TGA curves of the complexes are consistent with
the theoretical weight losses for their water contents.
3.6. Microbial activity
The results concerning in vitro antimicrobial activity of the lig-
ands and the complexes together with MIC values of compared
antibiotic and antifungal reagents are presented in Table 7.
Actually six bacteria and only one fungus have been stud-
ied in antimicrobial activity tests. The antimicrobial activity
results show that all of the complexes have selective antibacte-
rial effect on S. epidermidis. It is unambiguous that HL3, HL3·HCl,
[Zn(L1)2]·H2O and [Zn(L3)2]·2H2O have considerable antibacte-
Table 7
In vitro antimicrobial activity of the compounds (MIC, ␮g/ml).
Compound
Microorganisms
Saa
Sea
Ecb
Kpb
Pab
Pmb
Ca
HL1
–
–
312
–
2.4
2.4
78
–
2.4
–
19.5
–
–
0.125
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
2.00
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1.0
HL1·HCl
HL2
HL2·HCl
–
HL3
19.5
2.4
–
–
2.4
HL3·HCl
HL4
HL4·HCl
[Zn(L1)2]·H2O
[Zn(L2)2]
[Zn(L3)2]·2H2O
[Zn(L4)2]·2H2O
Zn(NO3)2·6H2O
Ciprofloxazin
Fluconazole
156
156
156
–
156
–
–
–
–
0.0625
–
0.0625
–
0.0312
–
Sa Staphylococcus aureus ATCC 6538; Se Staphylococcus epidermidis ATCC 12228; Ec Escherichia coli ATCC 8739; Kp Klebsiella pneumoniae ATCC 4352; Pa Pseudomonas aeruginosa
ATCC 1539; Pm Proteus mirabilis ATCC 14153; Ca Candida albicans ATCC 10231.
–, antimicrobial activity was not detected.
a
Gram(+).
Gram(−).
b

A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
205
4. Conclusions
In this work, we synthesized and characterized the chloro,
bromo, nitro derivatives of 2-(1H-benzimidazol-2-yl)-phenols and
their Zn(NO3)2 complexes. The metal:ligand ratio of the non-
electrolyte complexes is 1:2. The DFT calculations proved that
the bromo derivatives have higher stability than the nitro and
chloro derivatives. Antimicrobial activities of the compounds were
investigated towards six bacteria and a fungus. According to the
antimicrobial activity results, HL3 and [Zn(L1)2]·H2O are more
effective than Ciprofloxazin and [Zn(L2)2] exhibited microbial
activity as potent as Ciprofloxazin against S. epidermidis. HL3,
HL3·HCl, [Zn(L1)2]·H2O and [Zn(L3)2]·2H2O have very strong and
penetrating activity against Gram+ bacteria such as S. aureus and S.
epidermidis. It is noteworthy to point out that [Zn(L1)2]·H2O showed
strong antibacterial effect while the ligand itself had no any activity.
In conclusion, the structures of the mononuclear complexes were
verified by FT-IR, NMR, UV–vis and ESI-MS spectroscopic methods,
as well as by elemental analysis, molar conductivity and thermo
gravimetric analysis. All the analytical and spectral data are con-
sistent with the optimized structures. According to the geometry
optimization, Zn(II) ion is located on a distorted tetrahedral center
with the C N nitrogen and hydroxy oxygen atoms (Fig. 7).
Fig. 7. Optimized structure of Zn(L3)2 complex.
rial effect on S. aureus and S. epidermidis. Also, it is seen that
HL3 and [Zn(L1)2]·H2O are more active than Ciprofloxazin ref-
erence drug; and microbial activity of [Zn(L2)2] complex is
as potent as Ciprofloxazin against S. epidermidis. The antibac-
terial data indicate that the bromo substituted ligands and
their complexes have a very strong and penetrating activity
against Gram+ bacteria. For instance, HL3·HCl and [Zn(L1)2]·H2O
showed superior activity (MIC = 2.4 ␮g/ml for both of them)
against S. epidermidis (Gram+) than the reference Ciprofloxazin
(MIC = 156 ␮g/ml).
Microbial activity of HL1 and Zn(NO3)2 against the selected
microorganisms in our study is found to be insignificant. On
the other hand, [Zn(L1)2]·H2O complex showed superior activity
against S. epidermidis. The results of our study indicate that partic-
ularly HL3 and [Zn(L1)2]·H2O have displayed activity to generate
novel metabolites due to high affinities towards various receptors.
The strong antimicrobial activities of these compounds especially
against S. epidermidis warranted further investigation on these
compounds.
Acknowledgements
This work was supported by TUBITAK (The Scientific and Tech-
nological Research Council of Turkey). COST project number:
TBAG-U/185 (106T086).
References
[1] R. Bonnett, Chem. Rev. 63 (1963) 573–605.
[2] N.G. Brink, K. Folkers, J. Am. Chem. Soc. 72 (1950) 4442–4443.
[3] C.S.P. Sastry, P.Y. Naidu, S.S.N. Murty, Talanta 44 (1997) 1211–1217.
[4] C. Delescluse, M.P. Piechock, N. Ledirac, R.H. Hines, R. Li, X. Gidrol, R. Rahmani,
Biochem. Pharmacol. 61 (2001) 399–407.
[5] K.K. Mothilal, C. Karunakaran, A. Rajendran, R. Murugesan, J. Inorg. Biochem.
98 (2004) 322–332.
[6] E.J. Cardoso, A.F. Luna, J.P. Urizar, Acta Trop. 92 (2004) 237–244.
[7] M. Savlik, P. Polaskova, B. Szotakova, J. Lamka, L. Skalova, Res. Vet. Sci. 79 (2005)
139–147.
[8] R.G. Almeida, J.C. Florio, H.S. Spinosa, M.M. Bernardi, Neurotoxicol. Teratol. 24
(2002) 255–265.
[9] J. Gronvold, T.S. Svendsen, H.O. Kraglund, J. Bresciani, J. Monrad, Vet. Parasitol.
124 (2004) 91–99.
[10] B. Ülküseven, A. Tavman, G. Ötük, S. Birteksöz, Folia Microbiol. 47 (2002)
481–487.
3.7. Theoretical calculation and stability
According to the DFT calculations, HL1, HL3 and their Zn(II)
complexes, [Zn(L1)2]·H2O and [Zn(L3)2]·2H2O, have higher energy
values: −3695, −3441, −9205, −8695 a.u., respectively. The total
energy values of HL2, HL4 and their complexes are: −1344, −1073,
−4468, −3958 a.u., respectively. The DFT calculations prove that the
bromo derivatives have higher stability than the nitro and chloro
derivatives, comparing them with each other.
It is observed that HL1, having bromo and chloro substituents,
is more stable (total energy: −3695 a.u.) than HL3, having bromo
and nitro substituents (−3441 a.u.). It can be said that the nitro
substituent on the HL3 lead to a decrease in the stability. The
DFT calculations show that the stability of HL4 ligand is the low-
est among the ligands probably due to two nitro substituents
on the phenol and the benzimidazole benzene rings of it. Like-
wise, Zn(L4)2 has the highest energy among the complexes and
consequently the lowest stability: −3958 a.u. Also, this result is
consistent with the TGA data of [Zn(L4)2]·2H2O: it is observed that
onset of decomposition of [Zn(L4)2]·2H2O is at lower temperatures
than those of other complexes as explained in thermogravimetric
analyses.
[11] A. Tavman, N.M. Agh-Atabay, A. Neshat, F. Gücin, B. Dülger, D. Haciu, Transit.
Met. Chem. 31 (2006) 194–200.
˙
[12] A. Tavman, S. Ikiz, A.F. Bag˘cıgil, Y. Özgür, S. Ak, Russ. J. Inorg. Chem. 55 (2010)
215–222.
˙
[13] A. Tavman, S. Ikiz, A.F. Bag˘cıgil, Y. Özgür, S. Ak, J. Serb. Chem. Soc. 74 (2009)
537–548.
˙
[14] A. Tavman, S. Ikiz, A.F. Bag˘cıgil, Y.N. Özgür, S. Ak, Turk. J. Chem. 33 (2009)
321–331.
[15] A. Tavman, N.M. Agh-Atabay, S. Güner, F. Gücin, B. Dülger, Transit. Met. Chem.
32 (2007) 172–179.
[16] D.E. Fenton, Biocoordination Chemistry, Oxford University Press, Oxford, 1997.
[17] A. Tavman, S. Birteksöz, G. Ötük, Folia Microbiol. 50 (2005) 473–478.
[18] A. Tavman, B. Ülküseven, S. Birteksöz, G. Ötük, Folia Microbiol. 48 (2003)
479–483.
[19] S.O. Podunavac-Kuzmanovic, D.M. Cvetkovic, J. Serb. Chem. Soc. 72 (2007)
459–466.
[20] C.-Y. Guo, Y.-Y. Wang, K.-Z. Xu, H.-L. Zhu, P. Liu, Q.-Z. Shi, S.-M. Peng, Polyhedron
27 (2008) 3529–3536.
[21] E. Lukevics, P. Arsenyan, I. Shestakova, I. Domracheva, A. Nesterova, O. Pudova,
Eur. J. Med. Chem. 36 (2001) 507–515.
[22] N.M. Agh-Atabay, A. Neshat, T. Karabiyik, M. Somer, D. Haciu, B. Dülger, Eur. J.
Med. Chem. 42 (2007) 205–213.
[23] M. Sönmez, I. Berber, E. Akbas¸ , Eur. J. Med. Chem. 41 (2006) 101–105.
[24] H.F. Ridley, G.W. Spickett, G.M. Timmis, J. Het. Chem. 2 (1965) 453–456.
[25] A. Tavman, B. Ülküseven, Main Group Met. Chem. 24 (2001) 205–210.
[26] Clinical and Laboratory Standards Institute (CLSI), Methods for Dilution Antimi-
crobial Susceptibility Tests for Bacteria that Grow Aerobically, Approved
Standard, M7-A5, 2006, Wayne, PA, USA.
According to the geometry optimization of [Zn(L)2] structure
with DFT calculations, Zn is located on a distorted tetrahedral center
with the C N nitrogen and hydroxy oxygen atoms of benzimida-
zole moiety and phenol ring, respectively (molecular symmetry:
Cs). An exemplary optimized structure for Zn(L3)2 complex is given
in Fig. 7.

206
A. Tavman et al. / Spectrochimica Acta Part A 77 (2010) 199–206
[27] Clinical and Laboratory Standards Institute (CLSI), Reference Method for Broth
Dilution Antifungal Susceptibility Testing of Yeasts, Approved Standard M27-
A2, 2nd ed., 2002, Wayne, PA, USA.
[28] A. Tavman, Spectrochim. Acta A63 (2006) 343–348.
[29] D. Kanamori, Y. Yamada, A. Onoda, T.A. Okamura, S. Adachi, H. Yamamoto, N.
Ueyama, Inorg. Chim. Acta 358 (2005) 331–338.
[37] F.R. Prieto, J.C. Penedo, M. Mosquera, J. Chem. Soc. Faraday Trans. 94 (1998)
2775–2782.
[38] P.J. Black, M.I. Heffernan, Aust. J. Chem. 15 (1962) 862–864.
[39] R.M. Claramunt, C. Lopez, I. Alkorta, J. Elguero, R. Yang, S. Schulman, Magn.
Reson. Chem. 42 (2004) 712–714.
[40] G. Navarrete-Vazquez, L. Yepez, A. Hernandez-Campos, A. Tapia, F. Hernandez-
Luis, R. Cedillo, J. Gonzalez, A. Martinez-Fernandez, M. Martinez-Grueirod, R.
Castillo, Bioorg. Med. Chem. 11 (2003) 4615–4622.
[30] N. Ueyama, N. Nishikawa, Y. Yamada, T. Okamura, A. Nakamura, Inorg. Chim.
Acta 283 (1998) 91–97.
[31] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Com-
pounds, Part B, 5th ed., John Wiley & Sons Inc., New York, 1997.
[32] N. Sundaraganesan, C. Meganathan, B. Anand, C. Lapouge, Spectrochim. Acta
A66 (2007) 773–780.
[33] N. Sundaraganesan, B. Anand, F.-F. Jian, P. Zhao, Spectrochim. Acta A65 (2006)
826–832.
[41] W. Kemp, NMR in Chemistry: A Multinuclear Introduction, 2nd ed., McMillan
Education Ltd., London, 1998.
[42] K.K.M. Yusuf, R. Sreekala, Thermochim. Acta 179 (1991) 313–322.
[43] A.A. Soliman, W. Linert, Thermochim. Acta 338 (1999) 67–75.
[44] P.R. Chetana, X. Siddaramaiah, P.G. Ramappa, Thermochim. Acta 425 (2005)
13–21.
[34] D.S. Chowdhuri, A. Rana, M. Bera, E. Zangrando, S. Dalai, Polyhedron 28 (2009)
2131–2136.
[35] G.-X. Liu, K. Zhu, S. Nishihara, R.-Y. Huang, X.-M. Ren, Inorg. Chim. Acta 362
(2009) 5103–5108.
[45] S.-F. Si, R.-J. Wang, Y.-D. Li, Inorg. Chem. Commun. 6 (2003) 1152–1155.
[46] B.-M. Kukovec, Z. Popovic, J. Mol. Struct. 930 (2009) 121–125.
[47] F.-Q. Wang, D.-F. Weng, X.-J. Zheng, J.-J. Zhang, H. Ma, L.-P. Jin, Inorg. Chim. Acta
360 (2007) 2029–2038.
[36] S.L. Li, Y.Q. Lan, J.F. Ma, J. Yang, G.H. Wei, L.P. Zhang, Z.M. Su, Cryst. Growth Des.
8 (2008) 675–684.