Spectral characterization and antimicrobial activity of Cu(II) and Fe(III) complexes of 2-(5-Cl/NO2-1H-benzimidazol-2-yl)-4-Br/NO 2-phenols

Article abstract of DOI:10.1080/00958971003789835

The compounds of 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/ nitrophenols (HL_X : X = 1-4) and their copper(II) nitrate and iron(III) nitrate complexes have been synthesized and characterized. The structures of the complexes were confirmed on the basis of elemental analysis, thermal gravimetric analysis, molar conductivity and magnetic moment measurements, FT-IR, mass, and UV-Vis spectroscopy techniques. The complexes show high-thermal stability with >350°C m.p. In all complexes, the ligands are bidentate via one imine nitrogen and a phenolate oxygen. Cu(II) complexes having 1 : 2 M : L ratio are classified as non-electrolytes, whereas 1 : 1 M : L ratio is observed in Fe(III) complexes except [Fe(L₃) ₂(H₂O)₂](NO₃)· 3H ₂O. The antimicrobial activities of the ligands and the complexes were evaluated using the disc diffusion method in DMSO as well as minimum inhibitory concentration dilution method against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus mirabilis. Antifungal activities were reported for Candida albicans. The complexes [Fe(L₃)₂(H ₂O)₂](NO₃)· 3H₂O and [Cu(L₃)₂] · 2H₂O are more effective against S. epidermidis than ciprofloxacin.

Full text of DOI:10.1080/00958971003789835

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Spectral characterization and
antimicrobial activity of Cu(II) and
Fe(III) complexes of 2-(5-Cl/NO2-1H-
benzimidazol-2-yl)-4-Br/NO2-phenols
Aydin Tavman a , Ismail Boz b , A. Seher Birteksöz c & Adem Cinarli
a
a Faculty of Engineering, Department of Chemistry, Istanbul
University, 34320 Avcilar, Istanbul, Turkey
b Faculty of Engineering, Department of Chemical Engineering,
Istanbul University, 34320 Avcilar, Istanbul, Turkey
c Faculty of Pharmacy, Department of Pharmaceutical
Microbiology, Istanbul University, 34452 Beyazit, Istanbul, Turkey
Available online: 26 Apr 2010
To cite this article: Aydin Tavman, Ismail Boz, A. Seher Birteksöz & Adem Cinarli (2010): Spectral
characterization and antimicrobial activity of Cu(II) and Fe(III) complexes of 2-(5-Cl/NO2-1H-
benzimidazol-2-yl)-4-Br/NO2-phenols, Journal of Coordination Chemistry, 63:8, 1398-1410
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Journal of Coordination Chemistry
Vol. 63, No. 8, 20 April 2010, 1398–1410
Spectral characterization and antimicrobial activity of Cu(II)
and Fe(III) complexes of
2-(5-Cl/NO2-1H-benzimidazol-2-yl)-4-Br/NO2-phenols
¨
AYDIN TAVMAN*y, ISMAIL BOZz, A. SEHER BIRTEKSOZx
and ADEM CINARLIy
yFaculty of Engineering, Department of Chemistry, Istanbul University,
34320 Avcilar, Istanbul, Turkey
zFaculty of Engineering, Department of Chemical Engineering,
Istanbul University, 34320 Avcilar, Istanbul, Turkey
xFaculty of Pharmacy, Department of Pharmaceutical Microbiology,
Istanbul University, 34452 Beyazit, Istanbul, Turkey
(Received 19 March 2009; in final form 30 December 2009)
The compounds of 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitrophenols (HLX
:
X ¼ 1–4) and their copper(II) nitrate and iron(III) nitrate complexes have been synthesized
and characterized. The structures of the complexes were confirmed on the basis of elemental
analysis, thermal gravimetric analysis, molar conductivity and magnetic moment measure-
ments, FT-IR, mass, and UV-Vis spectroscopy techniques. The complexes show high-thermal
stability with 4350ꢀC m.p. In all complexes, the ligands are bidentate via one imine nitrogen
and a phenolate oxygen. Cu(II) complexes having 1 : 2 M : L ratio are classified as non-
electrolytes, whereas 1 : 1 M : L ratio is observed in Fe(III) complexes except
[Fe(L3)2(H2O)2](NO3) Á 3H2O. The antimicrobial activities of the ligands and the complexes
were evaluated using the disc diffusion method in DMSO as well as minimum inhibitory
concentration dilution method against Staphylococcus aureus, Staphylococcus epidermidis,
Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus mirabilis.
Antifungal
activities
were
reported
for
Candida
albicans.
The
complexes
[Fe(L3)2(H2O)2](NO3) Á 3H2O and [Cu(L3)2] Á 2H2O are more effective against S. epidermidis
than ciprofloxacin.
Keywords: Benzimidazole; Bromo/nitrophenols; Iron(III) and copper(II) complexes;
Antimicrobial activity
1. Introduction
The compound 2-(1H-benzimidazol-2-yl)-phenol and its derivatives are used as chelat-
ing agents with various transition metal complexes reported in [1–4]. For example,
a mixed-ligand Cr(III) complex [5], the tris-chelate Co(III) and the dinuclear
Cr(III) coordination compounds [6], and
2-(2-hydroxyphenyl)benzimidazole were reported. Complexes of iron(III) derived
a
Cu(II) complex [7] with
*Corresponding author. Email: atavman@istanbul.edu.tr
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2010 Taylor & Francis
DOI: 10.1080/00958971003789835

Benzimidazole phenols
1399
from 2-(20-hydroxyphenyl)benzimidazole (HPB) and 2-(20-hydroxybenzyl)-N-methyl-
benzimidazole (HMPB) were reported: Oxo-bridged and hydroxo complexes were
obtained as [Fe(PB)2]2O and [Fe(MPB)2(OH)2] Á 1/2H2O [3]. A series of binuclear
square-planar complexes of Cu(II) with hydroxy bridges and Fe(II) and Fe(III)
binuclear octahedral complexes with 1-(20-hydroxybenzyl)-2-(20-hydroxyphenyl)benz-
imidazole were synthesized [8]. In some U(VI) and Ce(IV) complexes of
1-(20-hydroxybenzyl)-2-(20-hydroxyphenyl)-benzimidazole, the IR spectral data sug-
gested that the ligand was monodentate through the tertiary nitrogen and that the
phenolic oxygen was free from coordination [9]. On the other hand, X-ray crystal
structure studies show coordination through C¼N nitrogen and phenolate oxygen
in the bis[2-(1H-benzimidazol-2-yl-ꢀN3)-phenolato-ꢀO]metal(II) type complexes
(metal : zinc [10], nickel [11], and cobalt [12]).
Antimicrobial activity of some 2-(1H-benzimidazol-2-yl)-phenol derivatives and their
metal complexes were investigated against selected microorganisms [1, 2, 13]. The
ligands were especially effective on Staphylococcus aureus; Ag(I) and Hg(II) complexes
showed high antimicrobial activity toward all bacteria; Fe(III) complexes exhibited
considerable activity against S. aureus and Staphylococcus epidermidis [1]. Some
benzimidazolyl phenols and their Fe(III) complexes showed considerable activity on
some bacteria and fungi [2, 13]. Co(II) and Ni(II) chelates of 2-(20-hydroxyphenyl)-
benzimidazole show antifungal activity against Alternaria alternata and Aspergillus
niger [14, 15].
Iron and copper are the essential elements that play vital roles in biological systems.
Thus, investigations of the coordination chemistry of Cu(II) continue to be stimulated
by interest in developing models for copper proteins and understanding the way they
react [16–18]. The extraordinary properties of these proteins, such as intense blue, are
related to the specific coordination geometries as well as the nature of the donors,
namely, histidine imidazole, cysteine sulfur, and methionine sulfur [19, 20]. One of the
most abundant transition elements is iron and, as an essential element, it has more roles
in biological systems than any other metal. One of the most important aspects is its
oxygen-binding function to hemoglobin, myoglobin, and cytochromes [21].
Studies on characterization and antimicrobial activity of benzimidazolyl phenol type
compounds and their complexes are rather scarce. In this study, we synthesize and
characterize new benzimidazole derivatives (scheme 1) and their Fe(III) and Cu(II)
complexes, and show their antimicrobial activities. The antibacterial and antifungal
activity of the compounds is evaluated by the disc diffusion method against six types of
bacteria and Candida albicans as yeast. Herein, we discuss the differences of metal ion
complexes with the free ligands in their structural–biological activity relationship.
2. Experimental
2.1. Chemistry and apparatus
All the chemicals and solvents were of reagent grade and purchased from Merck and
used without purification.
Analytical data were obtained with a Thermo Finnigan Flash EA 1112 analyzer.
Melting points were determined using an electrothermal melting point apparatus.

1400
A. Tavman et al.
R2
H
N
N
R1
HO
Scheme 1. The structure of the ligands: HL1: R1 ¼ Cl, R2 ¼ Br; HL2: R1 ¼ Cl, R2 ¼ NO2; HL3: R1 ¼ NO2,
R2 ¼ Br; HL4: R1 ¼ NO2, R2 ¼ NO2.
Molar conductivity of the complexes was measured on a WTW Cond315i conductivity
meter in DMSO at 25ꢀC. FT-IR spectra were recorded as KBr discs on a Nicolet 380
FT-IR 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. UV-Vis spectra were obtained on a Perkin Elmer
Lambda 25 UV-Vis spectrometer. Thermogravimetrꢁic1 studies were made on a TG-
60WS Shimadzu, with a heating rate of 10ꢀC min
and air flow at the rate of
50 mL minꢁ1. Magnetic measurements were carried out using MK1 Sherwood Scientific
apparatus at room temperature by Gouy’s method. Diamagnetic corrections were made
using Pascal’s constants.
2.2. Synthesis of the ligands: general procedure
The ligands were prepared according to the procedures in literature [4, 22]. For
instance, 2-(5-chloro-1H-benzimidazol-2-yl)-4-nitrophenol (HL2) has been obtained by
the reaction of 2-hydroxy-5-nitrobenzaldehyde (1.67 g, 10 mmol) with an equivalent of
NaHSO3 (1.04 g, 10 mmol) at room temperature in 25 mL ethanol for ꢂ5 h. The mixture
was treated with 4-chloro-1,2-phenylenediamine (1.42 g, 10 mmol) in dimethylforma-
mide (15 mL) and gently refluxed for 2 h (scheme 2). The reaction mixture was then
poured into ice water (500 mL), filtered, and crystallized from ethanol.
2.3. Synthesis of the complexes
2.3.1. [Cu(L1)2] · 2H2O. 162 mg HL1 (ꢂ0.5 mmol) suspended in methanol (10 mL) and
121 mg Cu(NO3)2 Á 3H2O (0.5 mmol) in methanol (5 mL) were added to the ligand
solution. After 2 h of reflux, the precipitate was filtered, washed with methanol (5 mL),
and dried at 70–80ꢀC. The other Cu(II) complexes were prepared in a manner similar to
[Cu(L1)2] Á 2H2O.
2.3.2. [Fe(L1)(OH)(H2O)3](NO3) · 3H2O. 162 mg HL1 (ꢂ0.5 mmol) suspended in
isopropanol (10 mL) and 210 mg Fe(NO3)3 Á 9H2O (40.5 mmol) in isopropanol
(5 mL) were added to the ligand solution. After 2 h of reflux, the precipitate was
filtered, washed with isopropanol (5 mL), and dried at 70–80ꢀC. The other Fe(III)

Benzimidazole phenols
1401
NO
NO
2
2
H
H
C H OH
2
5
NaO S
+
NaHSO
3
3
Room temperature
O
HO
HO
HO
NO
2
NO
2
NH
2
H
DMF reflux
–H
NaO S
3
+
NH
NH
O
2
Cl
HO
NH
2
HO
OH
SO Na
3
Cl
2
–NaHSO
3
NO
2
NO
2
H
N
H
N
–H
2
H
N
H
N
OH
Cl
Cl
HO
HL
2
Scheme 2. Synthesis of HL2.
complexes were prepared in a manner similar to [Fe(L1)(OH)(H2O)3](NO3) Á 3H2O; the
results are presented in table 1.
2.4. Determination of antimicrobial activity
Antimicrobial activities against S. aureus ATCC 6538, S. epidermidis ATCC 12228,
Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC 4352, Pseudomonas
aeruginosa ATCC 27853, Proteus mirabilis ATCC 14153, and C. albicans ATCC
10231 were determined by the microbroth dilutions technique using the National
Committee for Clinical Laboratory Standards (NCCLS) recommendations [23, 24].
Mueller-Hinton broth for bacteria, RPMI-1640 medium buffered to pH 7.0 with
morpholinepropanesulfonic acid (MOPS) for yeast strain was used as the test medium.
Serial twofold dilutions ranging from 5000 to 4.9 mg mLꢁ1 were prepared in the
medium. As control, antimicrobial effects of the solution were investigated against test
microorganisms. The inoculum was prepared 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
McFarland standard, diluted in broth media to give a final concentration of
5 ꢃ 105 cfu mLꢁ1 for bacteria and from 0.5 ꢃ 103 to 2.5 ꢃ 103 cfu mLꢁ1 for yeast in
the test tray. The trays were covered and placed in plastic bags to prevent evaporation.
Trays containing Mueller-Hinton broth were incubated at 35ꢀC for 18–20 h and
the trays containing RPMI-1640 medium were incubated at 35ꢀC for 46–50 h.

1402
A. Tavman et al.

Benzimidazole phenols
1403
The experiments were performed three times to minimize the error and the average
values were presented. The minimum inhibitory concentrations (MIC) were defined as
the lowest concentrations of compound giving complete inhibition of visible growth.
Ciprofloxacin and fluconazole were used as reference antibimicrobials for bacteria and
yeast, respectively. As control, antimicrobial effects of DMSO were investigated against
test microorganisms. According to the values of the controls, the results were evaluated.
3. Results and discussions
The analytical data and physical properties of the ligands and the complexes are
summarized in table 1.
3.1. General properties
All the Cu(II) complexes are in the ratio of 1 : 2 according to the analytical data. The
Fe(III) complexes have 1 : 1 M : L ratio except the HL3 complex. Molar conductivities of
the complexes support the suggested structures. [Fe(L3)2(H2O)2](NO3) Á 3H2O and
[Fe(L1)(OH)(H2O)3](NO3) Á 3H2O are ionic; the other Fe(III) complexes and the Cu(II)
complexes are non-ionic. High melting points of the complexes (4350ꢀC) show that the
compounds have high-thermal stability.
In the Fe(III) complexes, number of hydroxyl ions present are anomalous. Fe(III)
complexes of HL1, HL2, and HL4 which have 1 : 1 M : L ratio contain hydroxide as
ligand, whereas HL3 complex with 1 : 2 M : L ratio does not. The presence or absence of
hydroxide in the complexes is correlated with pH. Fe(III) salts hydrolyze easily
above pH 5 and thus, this easy hydrolysis leads to the formation of hydroxo complexes
[3, 13, 25]. Other factors which determined the number of hydroxides are acidity of the
ligands, chemical properties of the solvents, and excess of Fe(III) salt. All these factors
play a role in the hydrolysis of Fe(III) salts. The degree of hydrolysis is lower for Fe(III)
complex of HL1 than those of HL2 and HL4; there was no hydrolysis in Fe(III) complex
of HL3. Elemental analysis and ESI–MS spectral analysis results are in agreement with
the suggested composition formulae of the complexes (tables 1 and S2).
The room temperature effective magnetic moment values of Fe(III) complexes are in
the 3.96–5.06 BM range, indicating stabilization of the species having high-ferric spin
(S ¼ 5/2) state. These complexes may have six- or five-coordinate ferric complexes
(scheme 3) [13, 26, 27]. Magnetic moment values of Cu(II) complexes (between 1.58 and
1.66 BM) are closer to the expected value (1.73 BM) for a simple mononuclear Cu(II)
complex (scheme 4). These magnetic moment values can be assumed to square-planar
structure [25].
3.2. Thermal analysis
Major features of the thermal analysis of the complexes are summarized in table 2.
Thermal gravimetric analysis (TGA) curves of [Fe(L4)(OH)2H2O] Á H2O and
[Cu(L4)2] Á 2H2O are shown in figure S1. Samples were heated from room temperature
to 400ꢀC. Thermal analysis results exhibited valuable information about water

1404
A. Tavman et al.
+
Br
NO
2
H
N
H
N
–
NO
3
3H O
2
N
N
3H O
2
Cl
Cl
HO
H O
Fe
OH
O
2
Fe
OH
O
H O
OH
2
H O
OH
2
2
2
+
Br
H
N
–
3
NO
2
NO
N
H
N
O N
2
H O
2
O
O
Fe
3H O
OH
2
2
NO
N
2
H O
2
N
O N
2
HO
H O
Fe
O
N
H
OH
Br
2
Scheme 3. The proposed structures for the Fe(III) complexes.
R2
H
N
N
nH2O
R1
O
Cu
O
R1
N
N
H
R2
Scheme 4. The proposed structure for the Cu(II) complexes (R1 ¼ Cl, NO2, R2 ¼ Br, NO2; n ¼ 1 or 2).
coordination of the complexes. Thermal degradation occurred in three stages. At the
first stage, uncoordinated lattice water was lost through evaporation from 50ꢀC to
100ꢀC (table 2, first column). At the second stage, coordinated water was removed,
especially from Fe(III) complexes, at temperatures between 100ꢀC and 150ꢀC (table 2,
second column) [25, 28]. For the Cu(II) complexes, there are no weight losses
corresponding to removal of coordinated water, consistent with four coordination
(no water coordination). The Fe(III) complexes have coordinated and uncoordinated
water molecules and are five- or six-coordinate according to the analytical and thermal
analyses. For example, the TGA data are very informative for coordinated and

Benzimidazole phenols
1405
Table 2. TGA data of the complexes (thermal decomposition).
Weight loss (%)
250 300
5.4 7.1
Complex
Temperature (ꢀC)
100
4.2
8.7
2.9
9.9
4.1
5.9
4.6
4.7
150
4.9
11.7
3.3
13.1
4.3
7.4
5.5
200
5.2
350
8.7
24.5
10.7
56.0
11.5
67.3
10.7
24.5
400
[Cu(L1)2] Á 2H2O
22.0
32.0
37.8
67.2
63.2
74.5
32.1
72.3
[Fe(L1)(OH)(H2O)3](NO3) Á 3H2O
[Cu(L2)2] Á H2O
13.0
3.6
16.2
4.4
19.8
5.6
[Fe(L2)(OH)2(H2O)2] Á 3H2O
[Cu(L3)2] Á 2H2O
17.7
4.4
25.3
6.8
42.7
8.3
[Fe(L3)2(H2O)2](NO3) Á 3H2O
[Cu(L4)2] Á 2H2O
13.3
5.9
15.1
6.7
20.0
8.2
[Fe(L4)(OH)2H2O] Á H2O
6.4
8.7
16.1
19.2
uncoordinated water molecules of the five-coordinate [Fe(L4)(OH)2H2O] Á H2O : 4.7%
and 4.2% found and calculated, respectively, for one uncoordinated water molecule of
[Fe(L4)(OH)2H2O] Á H2O (figure S1).
In all complexes, weight losses above 250ꢀC can be explained in terms of cleavage of
Cl, Br, and nitro groups, and also as decomposition of nitrate ions. Above 350ꢀC, all
other organic parts of complexes are oxidized to carbon dioxide and water.
3.3. IR spectra
FT-IR spectral data of the ligands and the complexes are given in table S1. The ꢁ(O–H)
and ꢁ(N–H) vibration frequencies of the ligands exhibit only a single strong band at
ca 3300 cmꢁ1 caused by double intramolecular hydrogen bonding between the phenoxy
hydrogen and one of the imine nitrogens [13, 29–31]. These bands change significantly
upon metal complexation indicating deprotonation and subsequent coordination of the
phenoxy [32]. Appearance of strong or medium, broad bands between 3200 and
3500 cmꢁ1 in the complexes strongly support the presence of coordinated and
uncoordinated water molecules (figures S2 and S3). N–H stretching vibrations of the
ligands are observed between 3120 and 3275 cmꢁ1 in the complexes, suggesting that the
imine proton remains attached at N-1.
The ꢁ(C–H) and ꢂ(C–H) modes of ring residues in the ligands and the complexes are
observed between 3145–3070 cmꢁ1 and 845–730 cmꢁ1 (table S1), respectively. The ring
residue C¼C and the imidazole C¼N stretching frequencies are expected to appear
between 1650 and 1600 cmꢁ1 with their own characteristics for the ligands and the
complexes. Also, these bands are combined with coupled vibrations, such as ꢂ(C–H)
and ꢂ(N–H). Specific differences between spectra of the free ligands and the complexes
in this region support the formation of new complexes. In the spectra of free ligands and
their complexes, there is a band at around 1280 cmꢁ1 which is assigned to ꢁ(C–O) of the
phenolic group [33]. Phenolic C–O bands of the uncoordinated ligand shift to higher
frequencies during complex formation [34]; retention of the 1280 cmꢁ1 band in spectra
of the presented complexes suggests that the phenolic oxygens are coordinated to the
metal [26].
In IR spectra of HL2, HL3, HL4, and their complexes, the strong or medium bands
near 1500 cmꢁ1 (1532–1483) and in the 1377–1305 cmꢁ1 range are assigned to symmetric

1406
A. Tavman et al.
Figure 1. ESI-MS spectra of [Fe(L3)2(H2O)2](NO3) Á 3H2O.
and asymmetric ꢁ(NO2), respectively. The C–Br stretching vibration is at 500–550 cmꢁ1
as medium bands for HL1, HL3, and their complexes [35]. The C–Cl stretching
vibration is at 600–650 cmꢁ1 as medium or weak bands for HL1, HL2, and their
complexes [36]. Fe(III) complexes of HL1 and HL3 show strong bands at 1386 cmꢁ1 in
their IR spectra, supporting the presence of uncoordinated nitrate [37], also confirmed
by conductivity data.
3.4. Mass spectra
The ESI-MS spectral data of the complexes are given in table S2 as molecular ions with
relative abundance. The assignments of some intense ions are given in table S2 also. The
ESI-MS spectra of [Fe(L3)2(H2O)2](NO3) Á 3H2O and [Cu(L3)2] Á 2H2O are shown in
figures 1 and S4. Molecular ions of the complexes have been determined. The molecular
ions for [Cu(L1)2] Á 2H2O and [Cu(L2)2] Á H2O were observed with 100% relative
abundance. The other complexes showed their ions peak with various ratios. Also, the
peaks of the ligands (shown in table S2 as L) are easily determined in the mass spectra
of the complexes. It is known that chlorine, bromine, and copper have two isotopes:
35Cl(75.8%) : 37Cl(24.2%) (3 : 1); 79Br(50.7%) : 81Br(49.3%) (1 : 1); and 63Cu(69.2%) :
65Cu(30.8%) (2 : 1). Many isotopic patterns are identified for copper complexes that
include chlorine and bromine. For example, in the mass spectra of [Cu(L3)2] Á 2H2O, the
isotopic patterns are observed clearly (table S2): 764.6 (21.7%, [M ꢁ 1]þ, 65Cu); 762.6
(36.8%, [M ꢁ 3]þ, 63Cu); 334.3 (100%, L, 79Br); and 332.3 (97.6%, L, 81Br). Also, the
fragment of [Cu(L1)2] Á 2H2O complex produces many peaks. For example, M þ 2 peak
is observed at 746.7 mass number with 100% relative abundance. There are many
peaks between m/z 744 and m/z 748 because of various combinations of Cl, Br, and
Cu isotopes. No isotopic patterns are observed in spectra of [Fe(L4)(OH)2H2O] Á H2O,
as expected.

Benzimidazole phenols
1407
3.5. UV-Vis spectra
The UV-Vis spectral data are given in table 3. The sample visible electronic spectra
for Fe(III) and Cu(II) complexes are shown in figures S5 and S6.
The lower wavelength bands (200–300 nm) in the electronic spectra of the ligand and
the complexes correspond to ꢃ ! ꢃ* transitions of the aromatic rings. The medium or
weak bands above 300 nm are due to n ! ꢃ* transitions. Fe(III) complexes have broad,
strong bands in the 516–556 nm region caused by phenolic oxygen ! metal charge
transfer (L ! Fe3þ charge transfer; figure S5) [2]. The electronic spectra of the Cu(II)
complexes showed two or three bands at the visible region. Among them, the lowest
wavenumber bands are attributed to ligand to metal charge transfer transitions
(O ! Cu2þ). For example, in the spectra of [Cu(L1)2] Á 2H2O, the 497 nm band is due to
the L ! Cu2þ charge transfer transition (figure S6). The other two weak bands, 584
2
2
2
2
and 628 nm, may be assigned to B1g ! A1g and B1g ! Eg transitions, respectively.
These assignments can be attributed to a square-planar geometry for Cu(II) complexes
(scheme 4) [25, 38, 39].
3.6. Antimicrobial activity
The results concerning in vitro antimicrobial activity of the ligands and the
complexes together with MIC values of compared antibiotic and antifungal agents
are presented in table 4.
Table 3. UV-Vis spectral data of the compounds (in methanol).
Compound
Wavelength (ꢄmax (nm)) (log ")
Solution color
Colorless
Yellow
HL1
226(4.58), 292sh(4.27), 300(4.37), 327(4.44),
341(4.42)
212(4.70), 297(4.57), 325(4.62), 334sh(4.57),
356(4.21), 404br(3.83)
HL2
HL3
214(4.68), 230(4.30), 263sh(4.19), 269 (4.20),
349(4.11)
Yellow
HL4
227(4.44), 262sh(4.48), 269(4.49), 342(4.40),
413br(3.85)
Yellow
[A]
227(4.75), 230(4.73), 252sh(4.65), 300(4.41),
342(4.35), 548br(3.28)
Red
[Cu(L1)2] Á 2H2O
[B]
227(4.02), 261(3.65), 268sh(3.60), 303(3.41),
366(3.10), 497(2.04), 584(1.99), 628(1.96)
214(4.59), 253(4.01), 268sh(3.60), 297(4.01),
337(4.02), 527br(2.89)
213(4.52), 254(3.62), 264sh(3.62), 284(3.37),
372(3.11), 383(3.11), 476sh(2.37),
632(2.14)
Light brown
Red–violet
Dark yellow
[Cu(L2)2] Á H2O
[C]
217(4.67), 242(4.67), 252sh(4.60), 288(4.39),
348br(4.34), 388(4.07), 429(2.54), 556br(3.21)
223(4.63), 268(4.08), 276sh(4.00), 299(3.87),
375(3.19), 425(3.51), 436(3.52), 488 (2.82)
214(4.57), 223(4.63), 256(4.33), 267sh(4.31),
355br(4.28), 516br(3.00)
214(4.66), 236(4.68), 245sh(4.65), 252(4.64),
261sh(4.62), 274(4.61), 381(3.56), 459(3.07),
640(2.36)
Purple–violet
Orange
[Cu(L3)2] Á 2H2O
[Fe(L4)(OH)2H2O] Á H2O
[Cu(L4)2] Á 2H2O
Dark red
Light brown
[A]: [Fe(L1)(OH)(H2O)3](NO3) Á 3H2O, [B]: [Fe(L2)(OH)2(H2O)2] Á 3H2O, and [C]: [Fe(L3)2(H2O)2](NO3) Á 3H2O.

1408
A. Tavman et al.
Six bacteria and only one fungus have been studied in the antimicrobial activity tests.
Most of the compounds (HL1, HL2, HL4, and their complexes) and also
Fe(NO3)3 Á 9H2O and Cu(NO3)2 Á 3H2O have no significant antimicrobial activity in
this study. The antibacterial data indicate that both the bromo- and the nitro-
substituted ligand (HL3) have very strong and penetrating activity against S. aureus
(2.4 mg mLꢁ1) and S. epidermidis (19.5 mg mLꢁ1) which are Gram-positive bacteria.
Fe(III) and Cu(II) complexes of HL3 have a similarly very strong activity against the
above-mentioned bacteria. For instance, [Fe(L3)2(H2O)2](NO3) Á 3H2O and
[Cu(L3)2] Á 2H2O show superior activity against S. epidermidis organism (MIC value is
39 mg mLꢁ1 for both compounds) compared to the reference ciprofloxacin (MIC ¼
156 mg mLꢁ1). Superior activity of HL3, [Fe(L3)2(H2O)2](NO3) Á 3H2O and [Cu(L3)2] Á
2H2O against S. aureus and S. epidermidis is a valuable contribution to research on
metal-based drugs, indicating selective activity toward Gram-positive bacteria.
In the literature, there are numerous studies dealing with the antimicrobial activity of
coordination compounds [40–48]. Some complexes showed higher antimicrobial activity
than the ligands alone and the reference compounds [49–51]. In line with the results
published, there are several promising complexes which show some prospects in
antimicrobial activity. Therefore, there is a room for further studies on the metal
complexes. The results of our study indicate that HL3 ligand, [Fe(L3)2(H2O)2]
(NO3) Á 3H2O, and [Cu(L3)2] Á 2H2O complexes have potential to generate novel
metabolites, by displaying high affinities toward most of the receptors. The strong
antimicrobial activities of these complexes against S. aureus and S. epidermidis warrant
further investigation.
HL3 and its Fe(III) and Cu(II) complexes are effective against Staphylococcus-type
bacteria (Gram positive) only. However, at this stage it is impossible to find a simple
explanation for the antibacterial effect of HL3 and its complexes, while the other
complexes and HL1 ligand have no activity on these bacteria and further studies will
be needed to elucidate this phenomenon.
Table 4. In vitro antimicrobial activity of the compounds (MIC, mg mLꢁ1).
Microorganisms
Compound
Saa
Sea
Ecb
Kpb
Pab
Pmb
Ca
HL1
HL2
HL3
HL4
–
–
–
19.5
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
312
2.4
78
–
–
[A]
[B]
9.8
19.5
–
–
0.125
39
39
–
–
156
–
–
–
–
–
–
–
–
–
–
2.00
–
–
–
–
–
–
–
–
–
1.00
Fe(NO3)3 Á 9H2O
Cu(NO3)2 Á 3H2O
Ciprofloxacin
Fluconazole
–
0.0625
–
–
0.0625
–
–
0.0312
–
–
–
[A], [Fe(L3)2(H2O)2](NO3) Á 3H2O; [B], [Cu(L3)2] Á 2H2O.
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; and Ca,
Candida albicans ATCC 10231.
aGram-positive bacteria; bGram-negative bacteria.
– Denotes antimicrobial activity was not detected.

Benzimidazole phenols
1409
4. Conclusion
In this study, 2-(5-chloro/nitro-1H-benzimidazol-2-yl)-4-bromo/nitro-phenols ligands
(scheme 1) and their copper(II) nitrate and iron(III) nitrate complexes were synthesized
and characterized. Their antibacterial and antifungal activities were evaluated by the
disc diffusion method against six bacteria and C. albicans as yeast.
All of the Cu(II) complexes are of the bis-type (1 : 2) according to the analytical data.
The Fe(III) complexes have 1 : 1 M : L ratio except the HL3 complex. Fe(III) complexes
of HL1, HL2, and HL4 contain hydroxide as ligand because of hydrolysis, whereas the
HL3 complex does not. According to the magnetic moment measurements, Fe(III)
complexes are high spin (S ¼ 5/2) and are five- or six-coordinate. From the TGA data,
the presence of coordinated and uncoordinated water molecules was confirmed; Fe(III)
complexes have both coordinated and uncoordinated water molecules. Cu(II)
complexes do not contain coordinated water molecules; however, they contain water
molecules in the crystal. Complexation occurred via the nitrogen of C¼N and the
oxygen of phenol. Cu(II) complexes are square-planar structure according to the
UV-Vis spectra. Molar conductivity measurements also confirm the structures.
Molecular ions of the complexes and also the isotopic patterns have been determined
in the ESI–MS spectra.
The antibacterial data indicate that HL3 ligand having both the bromo and the
nitro substituents and its complexes show a very strong activity against S. aureus
and S. epidermidis (Gram-positive bacteria). [Fe(L3)2(H2O)2](NO3) Á 3H2O and
[Cu(L3)2] Á 2H2O complexes are more effective against S. epidermidis than ciprofloxacin.
The antimicrobial activity results of this study extend the literature. Various Cu(II)
complexes have considerable antimicrobial activities [44, 45, 50, 52], and Fe(III)
complexes are effective on various microorganisms [1, 2, 13, 41, 51, 53] with some
Fe(III) and Cu(II) complexes more effective than the free ligand [51, 54]. The presented
compounds warrant further investigation.
The proposed structures for the complexes are shown in schemes 3 and 4, in
accordance with the experimental data obtained from analytical data, magnetic
moments, molar conductivities, TGA, MS, FT-IR, and UV-Vis spectroscopic
techniques.
Acknowledgments
This work was supported by TUBITAK (The Scientific and Technological Research
Council of Turkey, COST project no. TBAG-U/185 (106T086).
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