Synthesis, characterization, and antimicrobial activities of two mononuclear metal(II) complexes with (Z)-3-hydroxy-4-(3-hydroxy-3- phenylacryloyl)phenyl benzoate

Article abstract of DOI:10.1080/00958972.2011.601459

Two mononuclear complexes with a βdiketone ligand (Z)-3-hydroxy-4-(3- hydroxy-3-phenylacryloyl)phenyl benzoate (L), [CoL₂(CH ₃CH₂OH)₂] (1), and [MnL₂(CH ₃CH₂OH)₂] (2) were prepared. Both complexes were characterized by X-ray crystallography, confirming that the central metal(II) are coordinated by four oxygens from two L and two oxygens from two ethanols. Both complexes were assayed for invitro antibacterial (Bacillus subtilis, Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter cloacae) activities and showed better antimicrobial activity against Gram positive strains than Gram negative strains.

Full text of DOI:10.1080/00958972.2011.601459

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Synthesis, characterization, and
antimicrobial activities of two
mononuclear metal(II) complexes
with (Z)-3-hydroxy-4-(3-hydroxy-3-
phenylacryloyl)phenyl benzoate
Suo-Ping Xu a , Ban-Feng Ruan b , Qi-Yu Pan c & Ren-Tao Hu c
a School of Chemistry and Chemical Engineering, Xuzhou Normal
University , Xuzhou 221116, P. R. China
b School of Medical Engineering, Hefei University of Technology ,
Hefei 230009, P. R. China
c Anhui Research Institute of Chemical Industry , Hefei 230039, P.
R. China
Published online: 14 Jul 2011.
To cite this article: Suo-Ping Xu , Ban-Feng Ruan , Qi-Yu Pan & Ren-Tao Hu (2011) Synthesis,
characterization, and antimicrobial activities of two mononuclear metal(II) complexes with (Z)-3-
hydroxy-4-(3-hydroxy-3-phenylacryloyl)phenyl benzoate, Journal of Coordination Chemistry, 64:14,
2489-2496, DOI: 10.1080/00958972.2011.601459
To link to this article: http://dx.doi.org/10.1080/00958972.2011.601459
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Journal of Coordination Chemistry
Vol. 64, No. 14, 20 July 2011, 2489–2496
Synthesis, characterization, and antimicrobial activities
of two mononuclear metal(II) complexes with
(Z)-3-hydroxy-4-(3-hydroxy-3-phenylacryloyl)phenyl benzoate
SUO-PING XUy, BAN-FENG RUAN*z, QI-YU PANx and REN-TAO HUx
ySchool of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou
221116, P. R. China
zSchool of Medical Engineering, Hefei University of Technology, Hefei 230009, P. R. China
xAnhui Research Institute of Chemical Industry, Hefei 230039, P. R. China
(Received 26 January 2011; in final form 8 June 2011)
Two mononuclear complexes with
a ꢀ-diketone ligand (Z)-3-hydroxy-4-(3-hydroxy-3-
phenylacryloyl)phenyl benzoate (L), [CoL2(CH3CH2OH)2] (1), and [MnL2(CH3CH2OH)2] (2)
were prepared. Both complexes were characterized by X-ray crystallography, confirming that
the central metal(II) are coordinated by four oxygens from two L and two oxygens from two
ethanols. Both complexes were assayed for in vitro antibacterial (Bacillus subtilis,
Staphylococcus aureus, Streptococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, and
Enterobacter cloacae) activities and showed better antimicrobial activity against Gram positive
strains than Gram negative strains.
Keywords: ꢀ-Diketone ligand; Mononuclear complexes; Antibacterial activity
1. Introduction
ꢀ-Diketones are important intermediates in organic synthesis. The high reactivity of
ꢀ-diketones such as 1,4-diphenyl-butane-1,3-dione, 1,4-dithiohene-butane-1,3-dione,
1,4-bis-(benzo(1,3)dio-butane-1,3-dione, 1,4-bis-(3-fluoro-4-methoxy-phenyl)-butane-
1,3-dione, 3-hydroxy-1,3-diphenyl-propenone, and 1,3-di-furan-2-yl-3-hydroxy-prope-
none have been reported [1–4]. ꢀ-Diketones and their derivatives also have a wide range
of applications in heat stabilizers, luminescence, catalysis, solvent extraction, and
pharmaceuticals [5–11]. There were many methods for the preparation of ꢀ-diketones,
but most of them could not provide satisfactory yields for a long time. Therefore,
development of direct and efficient procedures for this class of compounds has been the
target of synthetic organic chemistry. Recently, an operationally simple and new
approach to synthesize ꢀ-diketones from zinc-mediated C–C bond sigmatropic
rearrangement has been reported [12]. Herein, one bidentate ꢀ-diketone, (Z)-3-
hydroxy-4-(3-hydroxy-3-phenylacryloyl)phenyl benzoate (L), was synthesized in good
yield by microwave assistance and two mononuclear complexes were obtained by
*Corresponding author. Email: bf_ruan@163.com
Journal of Coordination Chemistry
ISSN 0095-8972 print/ISSN 1029-0389 online ß 2011 Taylor & Francis
DOI: 10.1080/00958972.2011.601459

2490
S.-P. Xu et al.
reacting L with CoCl2 ꢀ 6H2O and MnCl2 ꢀ 4H2O in ethanol:acetone (1 : 1). Both
complexes were assayed for antibacterial activities against three Gram positive bacterial
strains (Bacillus subtilis, Staphylococcus aureus, and Streptococcus faecalis) and three
Gram negative bacterial strains (Escherichia coli, Pseudomonas aeruginosa, and
Enterobacter cloacae) by the 3-(4,5-dimethyl-2-triazyl)-2,5-diphenyl-2H-tetrazolium
bromide (MTT) method.
2. Experimental
2.1. Materials and instruments
All chemicals were of reagent grade and used as received. UV spectra were recorded on
a U-3000 spectrophotometer. IR spectra were recorded on a Nexus 870 FT-IR. ESI-MS
spectra were recorded on a Mariner System 5304 mass spectrometer. Elemental analyses
were performed on a CHN–O-Rapid instrument and were within ꢁ0.4% of the
theoretical values. Melting points were measured on a Boetius micro melting point
apparatus.
2.2. Preparation of L, 1, and 2
Compound L was designed and synthesized from 2,4-dihydroxyacetophenone and
benzoyl chloride in acetone by microwave assistance. The ligand was reacted with
CoCl2 ꢀ 6H2O and MnCl2 ꢀ 4H2O in ethanol : acetone (1:1), respectively, and afforded
bis(benzoic acid 3-hydroxy-4-(3-hydroxy-3-phenyl-acryloyl)-phenyl ester)-bis-ethanol-
cobalt(II) (1) and bis(benzoic acid 3-hydroxy-4-(3-hydroxy-3-phenyl-acryloyl)-phenyl
ester)-bis-ethanol-manganese(II) (2) (scheme 1).
2.2.1. Preparation of L. K2CO3 (20 g) was slowly added to a round-bottom-flask
containing 2,4-dihydroxyacetophenone (3.04 g, 0.02 mol) and benzoyl chloride (5.6 g,
O
OH
H3C
O
Cl
OH
K2CO3/acetone
M. W, r .t
O
2
+
O
OH
O
OH
L
O
O
O
OH
H
O
2
ethanol
HO
O
O
O
OH
MCl2
+
M
O
acetone
O
O
H
OH
O
O
O
1-2
M = Co, Mn
Scheme 1. Synthesis of L, 1, and 2.

ꢀ-Diketone complexes
2491
0.04 mol) dissolved in acetone (50 mL). The mixture was microwave-irradiated (90 W)
for 2 h and then precipitated. After filtration, the yellow solid was washed with acetone
(100 mL) and water (200 mL), dried, and recrystallized from ethanol/acetone (1/1).
Yield: 80%, m.p.: 241–243ꢂC (lit. 240–243ꢂC [13]). UV (ꢁ nm): 377.5; 256.5. Selected IR
data (cmꢃ1, KBr): 3421.5 (m), 1734.8 (s), 1599.3 (s), 1569.3 (s), 1508.1 (s), 1260.2 (s),
1205.3 (m), 1138.5 (s), 1062.8 (m), 1023.3 (m), 767.0 (m), 710.2 (s); 1H-NMR (CDCl3) ꢂ
ppm: 15.46 (s, 1H), 12.23 (s, 1H), 8.20 (d, J ¼ 7.1 Hz, 2H), 7.95 (d, J ¼ 6.8 Hz, 2H), 7.86
(d, J ¼ 8.8 Hz, 1H), 7.66 (d, J ¼ 14.8 Hz, 1H), 7.55 (d, J ¼ 12.6 Hz, 4 H), 6.91 (d, J ¼ 2þ.4,
1H), 6.85 (d, J ¼ 11.2 Hz, 1H), 6.81 (s, 1H). ESI-MS: 361.10 (C22H17Oþ5 , [MþH] ).
Anal. Calcd for C22H16O5 (%): C, 73.33; H, 4.48. Found (%): C, 73.52; H, 4.45.
2.2.2. Compound 1. Compound L (0.360 g, 1 mmol) was added to an ethanol/acetone
(1/1) solution (5 mL) of CoCl2 ꢀ 6H2O (0.237 g, 1 mmol) and stirred at room temperature
for 15 min to give a clear solution. After standing for 10–15 days, the precipitates were
separated by filtration, washed with ethanol thrice, and dried. Single crystals of 1 were
obtained by slowly evaporating the methanol/ethyl ether solution. Yield: 75%,
m.p.: 250–252ꢂC. UV (ꢁ nm): 373.0; 255.5. IR (cmꢃ1, KBr): 3400.5 (m), 3125.2 (m),
1735.4 (s), 1595.9 (s), 1558.7 (s), 1507.8 (s), 1483.2 (s), 1433.5 (s), 1292.6 (m), 1240.4 (s),
1205.3 (s); 1138.8 (s), 1062.0 (s), 1023.5 (m), 768.6 (m), 706.0 (s). Anal. Calcd for
C48H42O12Co (%) : C, 66.28; H, 4.87. Found (%): C, 66.32; H, 4.84.
2.2.3. Compound 2. Prepared accordingly using L and MnCl2 ꢀ 4H2O. Yield: 81%,
m.p.: 227–229ꢂC. UV (ꢁ nm): 377.5; 255.0. IR (cmꢃ1, KBr): 3385.3 (m), 3138.2 (m),
1733.6 (s), 1595.6 (s), 1559.9 (s), 1507.1 (s), 1483.4 (s), 1430.9 (m), 1290.8 (s), 1252.7 (s),
1205.3 (s); 1139.6 (s), 1062.3 (s), 1023.0 (m), 769.2 (m), 705.6 (s). Anal. Calcd for
C48H42O12Mn (%): C, 65.59; H, 4.89. Found (%): C, 65.43; H, 4.82.
2.3. Crystal structure determinations and refinements
The crystallographic data for 1 and 2 were collected on a Bruker Smart 1000
˚
CCD area detector diffractometer equipped with Mo-Kꢃ (ꢁ ¼ 0.71073 A) radiation
using !-scan mode. Empirical absorption correction was applied to the data. Unit
cell dimensions were obtained with least-squares refinements, and all structures
were solved by direct methods with SHELXL-97. All non-hydrogen atoms were
located from the trial structure and then refined anisotropically. All hydrogens
were generated in idealized positions. All calculations were performed with
SHELXL-97 programs [14]. Other relevant parameters of the crystal structure
are listed in table 1.
2.4. Antimicrobial activity
The antibacterial activity of 1 and 2 was tested against B. subtilis, S. aureus, S. faecalis,
P. aeruginosa, E. coli, and E. cloacae using MTT medium. The MICs of the test
complexes were determined by a colorimetric method using the dye MTT [15]. A stock
solution of the synthesized complex (50 mg mLꢃ1) in DMSO was prepared and graded
quantities of the test complexes were incorporated in a specified quantity of sterilized

2492
S.-P. Xu et al.
Table 1. Crystallographic and experimental data for 1 and 2.
1
2
Empirical formula
Crystal system
Formula weight
Space group
C48H42O12Co
Triclinic
869.75
C48H42O12Mn
Triclinic
865.76
ꢀ
ꢀ
P1
P1
ꢂ
˚
Unit cell dimensions (A, )
a
b
c
ꢃ
ꢀ
ꢄ
7.2070(10)
9.4301(13)
16.5509(18)
106.360(2)
95.4320(10)
90.9180(10)
1073.4(2), 1
1.346
7.1380(10)
9.377(4)
16.578(2)
74.1510(10)
84.2010(10)
89.363(2)
1061.8(5), 1
1.354
0.376
3
˚
Volume (A ), Z
Calculated density (g cmꢃ3
)
Absorption coefficient (mmꢃ1
F(000)
)
0.464
453
451
Data/restraints/parameters
ꢅ range for data collection (ꢂ)
Rint
3728/0/296
2.25–25.02
0.0393
3698/0/287
2.26–25.021
0.0293
Final R indices [I 4 2ꢆ(I)]
Largest difference peak and hole (e A
Reflections collected/unique
R1 ¼ 0.0646, wR2 ¼ 0.1203
0.326 and ꢃ0.396
5624/3728
R1 ¼ 0.0579, wR2 ¼ 0.1329
0.275 and ꢃ0.226
5599/3698
ꢃ3
˚
)
P
P
P
P
R1 ¼ jjFoj ꢃ jFcj/ jFoj, bwR2 ¼ [ [w(Fo2 ꢃ Fc2)2]/ [w(Fo2)2]]1/2
.
Table 2. MICs of the compounds.
MICs (mg mLꢃ1
)
Gram positive
Gram negative
Compound
B. subtilis
S. aureus
S. faecalis
S. faecalis
E. coli
E. cloacae
1
2
L
6.25
12.5
25
12.5
6.25
12.5
6.25
6.25
12.5
12.5
12.5
25
12.5
12.5
25
6.25
12.5
25
PenicillinG
KanamycinB
1.562
0.39
1.562
1.562
1.562
3.125
6.25
3.125
6.25
3.125
3.125
1.562
liquid medium (MH medium for antibacterial activity). A specified quantity of the
medium containing the complex was poured into microtitration plates. Suspension of
the microorganism was prepared to contain approximately 105 cfu mLꢃ1 and applied to
microtitration plates with serially diluted complexes in DMSO to be tested and
incubated at 37ꢂC for 24 h. After the minimum inhibitory concentrations (MICs) were
visually determined on each of the microtitration plates, 50 mL of PBS (Phosphate
Buffered Saline 0.01 mol Lꢃ1, pH 7.4: Na2HPO4 ꢀ 12H2O 2.9 g, KH2PO4 0.2 g, NaCl
8.0 g, KCl 0.2 g, distilled water 1000 mL) containing 2 mg mLꢃ1 of MTT was added to
each well. Incubation was continued at room temperature for 4–5 h. The content of
each well was removed, and 100 mL of isopropanol containing 5% 1 mol Lꢃ1 HCl was
added to extract the dye. After 12 h of incubation at room temperature, the optical
density (OD) was measured with a microplate reader at 570 nm. The observed MICs are
presented in table 2.

ꢀ-Diketone complexes
2493
Figure 1. Molecular structure of 1 (all hydrogens and carbons of EtOH have been omitted for clarity).
Figure 2. Molecular structure of 2 (all hydrogens and carbons of EtOH have been omitted for clarity).
3. Results and discussion
Complexes of formula [L2M(CH3CH2OH)2] (M¼Co and Mn) were prepared as
described in section 2, in moderate yields (75–85%). IR spectra of all three complexes
show four bands at 1480–1600 cmꢃ1, characteristic of the mixed modes of vibrations
arising from normal coordinates having contributions from ꢇ(C¼O) and ꢇ(C¼C) of
ꢀ-diketone groups [16]. The UV spectra of the complexes display intense absorptions
at 255.0–258.5 nm (ꢈ ! ꢈ*) and 368.0–377.5 nm (n ! ꢈ*).
The structures of 1 and 2 were confirmed by single-crystal X-ray diffraction and are
shown in figures 1 and 2, respectively; bond distances and angles are provided in table 3.
Both complexes are electronically neutral mononuclear compounds. The central metals
(Co and Mn), on an inversion center, are in pseudo octahedral coordination geometry

2494
S.-P. Xu et al.
ꢂ
˚
Table 3. Selected bond lengths (A) and angles ( ) of 1 and 2.
1
Co–O1
Co–O1A
Co–O6
2.014(3)
2.014(3)
2.184(3)
Co–O2
Co–O2A
Co–O6A
2.033(2)
2.033(2)
2.184(3)
O1–Co–O2
O1–Co–O2A
O1–Co–O6
88.3(1)
91.7(1)
94.5(1)
O1–Co–O6A
O1–Co–O1A
85.5(1)
180.0(0)
2
Mn–O1
Mn–O1A
Mn–O6
2.084(2)
2.084(2)
2.245(3)
Mn–O2
Mn–O2A
Mn–O6A
2.118(2)
2.118(2)
2.245(3)
O1–Mn–O2
O1–Mn–O6A
84.4(9)
94.8(9)
O1–Mn–O6
85.1(9)
Figure 3. 1-D chains of 1 formed by intermolecular H bonds (O–H ꢀ ꢀ ꢀ O).
with two ethanols occupying both axial positions and oxygen donors from two
ꢀ-diketone fragments binding in equatorial positions; each bis-ꢀ-diketonate is essen-
tially planar [17]. The general M–O (M ¼ Co, Mn) bond lengths are in the range
˚
2.014(3)–2.245(3) A, unexceptional and similar to the corresponding bonds in other
cobalt and manganese diketonate complexes [18–20]. As shown in figures 3 and 4,

ꢀ-Diketone complexes
2495
Figure 4. 1-D chains of 2 formed by intermolecular H bonds (O–H ꢀ ꢀ ꢀ O).
intermolecular H-bonds (O–H ꢀ ꢀ ꢀ O) formed between adjacent molecules lead to 1D
chain structures for 1 and 2, respectively. The H ꢀ ꢀ ꢀ O distances are 2.018(3) and
ꢂ
ꢂ
˚
1.967(2) A and the OH ꢀ ꢀ ꢀ O angles are 167.9(2) and 163.7(2) for 1 and 2, respectively.
From MIC values (table 2), the complexes were more toxic towards Gram positive
strains than Gram negative strains when compared to the positive controls penicillin
and kanamycin, respectively. The reason may be the difference in the structures of the
cell walls [21]. The walls of the Gram negative cells are more complex than those of
Gram positive cells. Lipopolysaccharides form an outer lipid membrane and contribute
to the complex antigenic specificity of Gram negative cells. Anti-microbial activity of
complexes is due to either killing the microbes or inhibiting their multiplication by
blocking their active sites [22]. Since the molecular structures are quite similar, the
antibacterial activities of 1 and 2 are quite similar.
Acknowledgments
The work was co-financed by grants (Projects 30772627) from the National Natural
Science Foundation of China and (Projects 09KJD150005) from Province Natural
Science Foundation of Jiangsu, China.
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