Hydrothermal synthesis, crystal structure, and biological properties of a Mn(II) complex with phenylformic acid-imidazole ditopic ligand

Article abstract of DOI:10.1080/15533170802265780

A new Mn(II) coordination complex derived from 4-(imidazole-1-yl)-benzoic acid was synthesized by hydrothermal method and characterized by X-ray single crystal diffraction. Antimicrobial activity and DPPH free radical scavenging activity of the free ligand and its Mn(II) complex have been tested. The result indicated that the title complex shows stronger activity than the free ligand. The catalytic activity of the title complex [(L- H)2Mn(4H2O)] and the effect of added imidazole were also investigated for the disproportionation of hydrogen peroxide.

Full text of DOI:10.1080/15533170802265780

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Hydrothermal Synthesis, Crystal Structure, and
Biological Properties of a Mn(II) Complex with
Phenylformic Acid-Imidazole Ditopic Ligand
Jian Gao a b , Kai-Ju Wei b , Jia Ni c & Ju-Zhou Zhang d
a Department of Chemical Engineering, Lianyungang Technical College , Lianyungang, P.
R. China
b Department of Chemistry , University of Science and Technology of China , Hefei, P. R.
China
c Center Lab , Shantou University , Shantou, P. R. China
d Materials of Science and Engineering , University of Science and Technology of China ,
Hefei, P. R. China
Published online: 04 Sep 2008.
To cite this article: Jian Gao , Kai-Ju Wei , Jia Ni & Ju-Zhou Zhang (2008) Hydrothermal Synthesis, Crystal Structure, and
Biological Properties of a Mn(II) Complex with Phenylformic Acid-Imidazole Ditopic Ligand, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:6, 562-566
To link to this article: http://dx.doi.org/10.1080/15533170802265780
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 38:562–566, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533170802265780
Hydrothermal Synthesis, Crystal Structure, and Biological
Properties of a Mn(II) Complex with Phenylformic
Acid-Imidazole Ditopic Ligand
Jian Gao,1,2 Kai-Ju Wei,2 Jia Ni3 and Ju-Zhou Zhang4
1Department of Chemical Engineering, Lianyungang Technical College, Lianyungang, P. R. China,
2Department of Chemistry, University of Science and Technology of China, Hefei, P. R. China
3Center Lab, Shantou University, Shantou, P. R. China
4Materials of Science and Engineering, University of Science and Technology of China, Hefei, P. R. China
mutation, water oxidation, and ribonucleotide reduction.[12,13]
A new Mn(II) coordination complex derived from 4-(imidazole-
1-yl)-benzoic acid was synthesized by hydrothermal method and
characterized by X-ray single crystal diffraction. Antimicrobial ac-
tivity and DPPH free radical scavenging activity of the free ligand
and its Mn(II) complex have been tested. The result indicated that
the title complex shows stronger activity than the free ligand. The
catalytic activity of the title complex [(L−H)2Mn(4H2O)] and the
effect of added imidazole were also investigated for the dispropor-
tionation of hydrogen peroxide.
Herein we report the synthesis of a Mn(II) coordination com-
plex derived from the ligand 4-(imidazole-1-yl)-benzoic acid,
which has two kinds functional coordination groups, carboxy-
late and imidazole moieties, as shown in Scheme 1. The complex
was synthesized by hydrothermal method and characterized by
X-ray single crystal diffraction. Detailed structural, catalysis to
the disproportionation of H2O2, capacity to scavenge free DPPH
radical, and antimicrobial activity studies are also reported
hereunder.
Keywords 4-(imidazole-1-yl)-benzoic acid, Mn(II) complex, single
crystal structure, antimicrobial activity, antioxidant activ-
ity, catalytic activity
EXPERIMENTS
Materials and Methods
All starting chemicals were of reagent-grade quality and were
obtained from commercial sources. All reagents and solvents
were dried and purified by usual methods. H NMR spectra
were recorded on a Bruker 300 Ultrashield spectrometer op-
erating at 300 MHz. The FT-IR spectra were recorded in the
region 400–4000 cm−1 on a Bruker EQUINOX 55 VECTOR22
spectrophotometer, and the samples were prepared using KBr
pellets. Elemental analyses were carried out with an Elementary
Vario EL-III analyzer (Germany).
INTRODUCTION
It is well known that small molecule model complexes are
useful in studying more complex biological systems,[1] espe-
cially given the fact that structural geometries of some model
complexes are quite comparable to those in the proteins.[2] Im-
idazole is ubiquitous in biology and chemistry; therefore, it is
of considerable interest as a unit of ligand since its presence in
many biological systems provides a potential binding site for
metal ions.[3,4] Imidazole-containing compounds are reported
to have biological functions such as thrombin-inhibitor, antiox-
1
idant, antifungal, and antimicrobial activity.[5–11] Manganese is Preparation of the Ligand and Complex
known to participate in a variety of biological reactions, such as
Synthesis of 4-(Imidazole-1-yl)-Benzaldehyde
hydrogen peroxide decomposition, superoxide anion (O−2 ) dis-
A mixture of 4-fluorobenzaldehyde (5.58 g, 45 mmol),
imizole (2.05 g, 30 mmol), anhydrous K2CO3 (4.14 g, 30
mmol), and 18-Crown-6 (0.159 g, 0.6 mmol) in anhydrous
DMF (50 mL) was stirred for 48 h under dry nitrogen at 120◦C
After the reaction mixture was cooled, the solvent was removed
by vacuum distillation, and ice-water was added to the residue.
The product was isolated by filtrating to obtain the straw yellow
solid. Yield: 4.2 g, 81%. IR (cm−1, KBr): 3110 (m), 1687 (s),
1607 (s), 1525 (s), 1483 (s), 1400 (w), 1375 (w), 1311 (s), 1270
(m), 1171 (m), 1061 (m), 834 (s). 1H NMR (400 MHz, CDCl3,
Received 4 June 2007; accepted 2 March 2008.
The project was supported by Open-end Funds of Jiangsu
Key Laboratory of Marine Biotechnology, Huaihai Institute of
Technology (No. 2006HS007) and Lianyungang Technical College
(No. YKJ200712).
Address correspondence to Jian Gao, Department of Chemical
Engineering, Lianyungang Technical College, Lianyungang, 222006,
P. R. China. E-mail: gaojian553@163.com.
562

MN(II) COMPLEX SYNTHESIS AND STRUCTURE
563
TABLE 1
Crystallographic data for the complex [(L−H)2Mn(4H2O)]
Formula
C20H22MnN4O8
Formula weight
T/K
λ(Mo-Kα) A
501.36
293(2)
˚
SCHEME 1. Preparation of the ligand.
0.71073
Monoclinic
0.28 × 0.26 × 0.25
P2(1)/c
12.2841(10)
11.0162(10)
7.9642(7)
90
96.791(2)
90
1070.19(16)
1.556
Crystal system
Crystal size/mm3
Space group
ppm) δ: 9.2 (s, 1H), 8.03 (d, 2H), 8.00 (s, 1H), 7.59 (d, 2H),
7.43 (s, 1H), 7.26 (s, 1H)
˚
a/A
˚
b/A
Synthesis of 4-(Imidazole-1-yl)-Benzoic Acid (L)
˚
c/A
A mixture of 4-(imidazole-1-yl)-benzaldehyde (3.12 g,
20 mmol) and 6M NaOH (4 mL) was stirred at 0◦C◦ Then
30% H2O2 was added dropwise. The A mixture was filtrated
after it was stirred at 0◦C for 12 h and at room temperature for
12 h. The filtrate was then adjusted to pH 5.0 with diluent hy-
drochloric acid to obtained large amount of solid product. The
resulting solid product was washed with water and dried. Yield:
2.86 g, 76%. IR (cm−1, KBr): 3121 (m), 2430 (w), 1925 (w),
1700 (s), 1608 (s), 1525 (s), 1491(w), 1431 (w), 13,752 (w),
α/deg
ß /deg
γ /deg
3
˚
V /A
Dc/Mg m−3
Z
2
518
0.673
5739
1878
0.0188
1878/0/151
0.0597, 0.1258
0.0611, 0.1312
1.030
F(000)
µ/mm−1
Reflections collected
Reflections unique
Rint
Data/restraints/parameters
R1, wR2[I> 2σ(I)]
R1, wR2 (all data)
GOF on F2›
1
1309 (s), 1251 (s), 1182 (m), 1116 (m), 1059 (s), 962 (m). H
NMR (300 MHz, CDCl3, ppm) δ: 8.380 (s, 1H), 8.064–8.035
(d, 2H), 7.843–7.784 (t, 3H), 7.144 (s, 1H)
Synthesis of the Title Complex [(L−H )2Mn(4H2O)]
Fresh Mn(ClO4)2·6H2O (0.361 g, 1.0 mmol) and 4-
(imidazole-1-yl)-benzoic acid (0.188 g, 1.0 mmol) were mixed
in water with stirring, then the mixture was sealed in a 30-mL
stainless steel reactor with Teflon liner at 160◦C for 72 h, result-
ing in the formation of light yellow crystals of the title complex.
Yield: 36%. The C, H, and N content were determined by el-
emental analysis: Anal. Calcd. for Mn (C10H7N2O2)2(4H2O)
(%): C, 47.87; H, 4.39; N, 11.17. Found: C, 47.66; H, 4.38; N,
11.46.
cell at 16◦C, 1 mL of the above solution was stirred with 5 mL
of water and 1 mL of an aqueous imidazole solution (6.81 mg,
0.1 × 10−3 mol). With a vacuum pump, an average 80 mbar
pressure above the solution was obtained and measured with
a pressure gauge. Then, hydrogen peroxide (1 mL; H2O2 30%
w/w) was introduced in the stirred solution and the evolved
oxygen was measured.
Crystallographic Study
X-ray diffraction data were collected on a Bruker APEX area-
detector diffractometer at 293 K using ω rotation scans with Mo
DPPH Free Radical Scavenging Activity
˚
Kα radiation (λ = 0.71073 A). The structures were solved by
The free-radical scavenging capacity of different concentra-
tions of Ligand L and the title complex [(L−H)2Mn(4H2O)]
was tested by their ability to bleach the stable 1,1-diphenyl-
2-picrylhydrazyl radical (DPPH) according to the methods of
Lamaison et al.[14] Various concentrations of the test compounds
in absolute methanol were added to an methanolic solution
of DPPH radical (final concentration of DPPH was 1 × 10−4
mmol/L). The mixture was shaken vigorously and allowed to
stand for 30 min; absorbance at 517 nm was determined by
a Perkin-Elmer U-2001 spectrophotometer, and the percentage
inhibition was determined by comparing the absorbance values
direct methods and refined with full-matrix least-squares tech-
nique using SHELXTL. Anisotropic thermal parameters were
applied to all non-hydrogen atoms. All of the hydrogen atoms
in these structures are located from the differential electron den-
sity map and constrained to the ideal positions in the refinement
procedure. The crystallographic calculations were conducted
using the SHELXL-97 programs. Crystal data and experimental
details for the crystal are given in Table 1.
Hydrogen Peroxide Disproportionation
Ligand L and the title complex [(L−H)2)Mn(4H2O)] (4 × of test and control tubes. IC50 values were obtained from the
10−5 mol) was dissolved in DMSO (10 mL). In a thermostated plot, drawn for concentration in microgram versus percentage

564
J. GAO ET AL.
Fig. 1. A stereoview of [(L−H)2Mn(4H2O)] with the atom numbering scheme (ellipsoids at 30% probability).
inhibition. All tests and results were undertaken on three repli- centers from H2O. Thus, MnN2O4 tetragonal bipyramid coor-
cates and the results averaged.
dination geometry is ensured. The apical positions are occupied
by atoms N(1) and N(1A). [N(1)-Mn(1)-N(1)#1: 180.00(18)].
The Mn atom lies in the basal plane [O(3)/O(4)/O(3A)/O(4A)].
Antimicrobial Activity Screening
˚
The Mn-N bond length 2.243(3) A and Mn-O(H2O) bond length
The two compounds L and [(L−H)2Mn(4H2O)] were
screened for their toxicity by testing antimicrobial activity
against bacterial strands using the agar diffusion method in the
same procedure as in Gao et al.[15] Compounds dissolved in
dimethylformamide (DMF) were tested against standard strains
of Candida albicans CMCC (F) 98 001, Staphyloccus aureus
CMCC (B) 26 003, Bacillus pumilus CMCC (B) 63 202, and
Klebosiella pneumoniae CMCC (B) 46 117. All tests were re-
peated three times and average data were taken as the final result.
[16]
˚
2.144(3) (or 2.189(3)) A agree well with literature reports.
The dihedral angles of the two aromatic rings (benzene ring and
imidazole ring) and benzene ring to carboxyl plane are 6.4◦ and
22.4◦, respectively. It indicates that slight distort was produced.
H-bonds are observed between the carboxylate groups and the
coordinated water molecules (Figure 2), 3D architecture was
formed and stabilized by the above hydrogen bonding.
Symmetry transformations used to generate equivalent
atoms:
RESULTS AND DISCUSSION
#1 − x, −y, −z
Description of the Structure
The structure of [(L−H)2Mn(4H2O)] is shown in Figure 1.
Selected bond distances and angles are listed in Table 2. The
complex consists of a central manganese atom surrounded by
Catalytic Activity
The catalytic activity of the title complex [(L−H )2Mn(4H2O)]
two 4-(imidazole-1-yl)-benzoic acid ligands and four O donor and the effect of added imidazole were investigated for the
TABLE 2
◦
˚
Selected bond distances (A) and bond angles ( ) for [(L−H)2Mn(4H2O)]
Bond
Dist.
Bond
Dist.
Mn(1)-O(3)#1
Mn(1)-O(3)
Mn(1)-O(4)
2.144(3)
2.144(3)
2.189(3)
Mn(1)-O(4)#1
Mn(1)-N(1)
Mn(1)-N(1)#1
2.189(3)
2.243(3)
2.243(3)
Angle
(◦)
Angle
(◦)
O(3)#1-Mn(1)-O(3)
O(3)#1-Mn(1)-O(4)
O(3)-Mn(1)-O(4)
O(3)#1-Mn(1)-O(4)#1
O(3)-Mn(1)-O(4)#1
O(4)-Mn(1)-O(4)#1
O(3)-Mn(1)-N(1)
180.00(17)
92.68(12)
87.32(12)
87.32(12)
92.68(12)
180.00(14)
92.41(14)
87.59(14)
O(4)-Mn(1)-N(1)
93.21(12)
86.79(12)
92.41(14)
87.59(14)
86.79(12)
93.21(12)
180.00(18)
O(4)#1-Mn(1)-N(1)
O(3)#1-Mn(1)-N(1)#1
O(3)-Mn(1)-N(1)#1
O(4)-Mn(1)-N(1)#1
O(4)#1-Mn(1)-N(1)#1
N(1)-Mn(1)-N(1)#1
O(3)#1-Mn(1)-N(1)

MN(II) COMPLEX SYNTHESIS AND STRUCTURE
565
Fig. 2. A packing diagram for[(L−H)2Mn(4H2O)]. Hydrogen bonds are indicated by dashed lines.
disproportionation of hydrogen peroxide. Figure 3 presents the the reaction. It was suggested that imidazole may be essential
evolution of oxygen pressure in absence or presence of the im- in the catalysis disproportionation of H2O2 by the manganese
idazole. In absence of the imidazole, the complex has a very complex. The result is consistent with the former report.[16]
weak ability to catalyze the reaction. The experment result indi-
cated that the hydrogen peroxide disproportion catalytic activity
Antioxidant Activity
of the Mn(II) complex was found remarkably only in the pres-
The lower the IC50 values, the higher the antioxidant activity.
ence of added imidazole, and imidazole may be essential in
From the IC50 values (Table 3), we can see that the two com-
pounds show different DPPH free radical scavenging activity.
[(L−H)2Mn(4H2O)] has high activity compared to the ligand L,
but its activity is somewhat lower than Vitamin C.
Antimicrobial Activity
From Table 4 we can see that the two compounds were active
against four test organisms but showing different antimicrobial
activities. The complex [(L−H )2Mn(4H2O)] was more active
than its parent ligand L, which may be attributed to its higher
lipophilic character. The highest antimicrobial activity among
TABLE 3
IC50 values of L and [(L−H )2Mn(4H2O)]
Compound
IC50 (µM)
L
96.2
36.3
25.1
[(L−H )2Mn(4H2O)]
Vitamin C∗
Fig. 3. Hydrogen peroxide disproportionation by the title complex curves:
(A) complex with and addition of imidazole; (B) complex without addition of
imidazole.
∗Cited from reference Vekateswarlu et al.[17]

566
J. GAO ET AL.
TABLE 4
The diameter of inhibition zone (mm) of L and [(L−H)2Mn(4H2O)]
Diameter of inhibition zone (mm)
Candida
albicans
Staphyloccus
aureus
Bacillus
pumilus
Klebosiella
pneumoniae
Compound
L
Concentration (mmol/L)
5.0
2.5
1.2
0.6
5.0
2.5
1.2
0.6
12.4
11.1
9.2
6.16
15.2
14.8
11.9
11.0
15.9
13.8
12.1
9.0
20.3
16.3
15.9
14.8
11.6
10.5
9.7
11.8
11.2
9.9
7.9
7.2
[(L−H)2Mn(4H2O)]
16.0
15.1
14.5
13.1
16.0
13.9
13.5
12.1
the group of these organisms was observed against Staphyloc-
cocus aureus. In the range of 0.6–5.0 mmol/L, the compounds
were more active against the test strains with the increase of
concentration.
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Crystallographic data have been deposited with the CCDC
(12 Union Road, Cambridge, CB2 1EZ, UK) and are avail-
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