КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 4, с. 240-245
УДК 541.49
NEW VANADIUM AND ZINC COMPLEXES WITH SCHIFF BASE LIGAND N,N'-£/s(3-ETHOXY-2-HYDROXYBENZYLIDENE)ETHYLENEDIAMINE: SYNTHESIS, STRUCTURES, AND BIOCHEMICAL PROPERTIES
© 2014 H. Y. Liu, C. Li, and J. J. Ma*
Hebei Key Laboratory of Bioinorganic Chemistry, College of Sciences, Agricultural University of Hebei,
Baoding, 071001 P.R. China *E-mail: majingjun71@aliyun.com Received April 29, 2013
The Schiff base ligand N,N'-bis(3-ethoxy-2-hydroxybenzylidene)ethylenediamine (H2L) reacting with vanadyl acetylacetonate and zinc chloride, respectively, in methanol gave the complexes [VOL] ■ H2O (I) and [ZnL(OH2)] (II). Both complexes were characterized by elemental analyses and IR spectroscopic method in the solid state. Single crystal X-ray analysis was performed, which reveals that both of them are mononuclear complexes. Complex I crystallizes in the monoclinic space group P2i/c with unit cell dimensions a = 9.4387(7), b = 16.996(1), c = 12.758(1) А, в = 98.269(2)°, V = 2025.4(3) A3, Z = 4, R1 = 0.0365, and wR2 = 0.0946.
Complex II crystallizes in the tetragonal space group P42\m with unit cell dimensions a = b = 22.0489(8), c = 4.9846(4) A, V = 2423.3(2) A3, Z = 4, R1 = 0.0890, and wR2 = 0.2278. The V atom in I and the Zn atom in II are in square pyramidal coordination. Anbacterial activities of the Schiff base ligand and the complexes have been studied on the strains B. subtilis, E. coli and S. aureus.
DOI: 10.7868/S0132344X14040045
INTRODUCTION
Schiff bases in general have been shown to be biological active. A great deal of Schiff bases were reported to possess antibacterial, antifungal and antitumor activities [1—3]. The effect of presence of various sub-stituents in the phenyl rings of aromatic Schiff bases on their antibacterial activity has been reported [4]. Due to their multiple implications, the transition metal complexes with Schiff bases, as ligands, are of paramount scientific interest. It has been found that in general the complexation of Schiff bases with most transition metal atoms influences their antibacterial activities [5—7]. With this view and in continuation of work on the study of Schiff bases and their metal complexes, herein we report two new vanadium and zinc complexes, [VOL] ■ H2O (I) and [ZnL(OH2)] (II), where L is the dianionic form of N,N'-bis(3-ethoxy-2-hydroxybenzylidene)ethylenediamine (H2L). The antibacterial activity of the Schiff base and their complexes are reported against B. subtilis, E. coli and S. aureus.
EXPERIMENTAL
3-Ethoxysalicylaldehyde and ethylenediamine were purchased from Merck and Fluka, and used as received. The Schiff base ligand was prepared in over 90% yield according to the literature method [8]. All other chemicals and solvents used in this work were of analytical grade available commercially and used without further purification. Elemental analyses (carbon, hydrogen, and nitrogen) of the compounds were obtained from a Carlo ERBA Model EA 1108 analyz-
er. Infrared spectra were collected by using KBr pellets on a Jasco-5300 FT—IR spectrophotometer. Solution electrical conductivity was measured with a DDS-11A conductivity meter.
Synthesis of I. Vanadyl acetylacetonate (0.01 mmol, 2.65 g) dissolved in methanol (30 mL) was added dropwise to a stirred methanolic solution (30 mL) of H2L (0.01 mol, 3.56 g). The mixture was gently refluxed for 2 h, then most of the solvent was evaporated by distillation. After cooling, the resulting brown solid was filtered off, washed with cold methanol, and dried in a vacuum containing anhydrous CaCl2. The yield was 3.17 g (72%).
For C20H24N2O6V
anal. calcd., %: C, 54.7; H, 5.5; N, 6.4.
Found, %: C, 54.5; H, 5.6; N, 6.3.
Brown block-like single crystals of the complex, suitable for single crystal X-ray diffraction, were obtained by slow evaporation of a methanol solution containing complex I.
Synthesis of II. Zinc chloride (0.01 mmol, 1.36 g) dissolved in methanol (30 mL) was added dropwise to a stirred methanolic solution (30 mL) of H2L (0.01 mol, 3.56 g). The mixture was gently refluxed for 2 h, then most of the solvent was evaporated by distillation. After cooling, the resulting colorless solid was filtered off, washed with cold methanol, and dried in a vacuum
Table 1. Crystallographic data and refinement parameters for complexes I and II
Parameter Value
I II
Formula weight 439.35 437.78
Crystal system Monoclinic Tetragonal
Space group P21/c P42im
Unit cell dimensions:
a, A 9.4387(7) 22.0489(8)
b, A 16.996(1) 22.0489(8)
c, A 12.758(1) 4.9846(4)
ß, deg 98.269(2)
V, A3 2025.4(3) 2423.3(2)
Z 4 4
p, g cm-3 1.441 1.200
p., mm-1 0.529 1.041
T T J min J max 0.8880, 0.9016 0.7736, 0.8188
Reflections collected 19368 21635
Reflections unique 3769 2330
Reflections observed (I > 2ct(I)) 3165 1732
Parameters 270 134
Restraints 2 1
R1, wR2 (I> 2a(I)) 0.0365, 0.0946 0.0890, 0.2278
R1, wR2 (all data) 0.0459, 0.1028 0.1258, 0.2452
Goodness-of-fit on F 2 1.040 1.203
Largest diff. peak and hole, e A-3 0.297, -0.236 0.726, -0.603
containing anhydrous CaCl2. The yield was 2.82 g (64%).
For C2oH24N2O5Zn
anal. calcd., %: Found, %:
C, 54.9; C, 54.7;
H, 5.5; H, 5.7;
N, 6.4. N, 6.5.
Colorless block-like single crystals of the complex, suitable for single crystal X-ray diffraction, were obtained by slow evaporation of a methanol solution containing complex II.
X-ray crystallography. Suitable X-ray quality crystals of the complexes were pick up under a microscope and investigated in a diffraction experiment at 298(2) K on a Bruker Apex II diffractometer with monochromated Mo^ radiation (X = 0.71073 A) obtained from a graded multilayer X-ray optics. The structures were solved by direct methods with SHELXS-97 [9], and refined with full-matrix least-squares techniques on F2 with SHELXL-97 [9]. The C- and O-bonded hydrogen atoms were calculated in an idealized geometry, riding on their parent atoms, with distances restrained to 0.93—0.97 A for C—H. The water hydrogen atoms were located from difference Fourier maps and refined isotropically with O—H distances restrained to 0.85(1) A. The crystal data and refinement parameters are listed
Table 2. Selected bond lengths (A) and angles (deg) for complexes I and II
O(5)V(1)O(2) O(2)V(1)O(1) O(2)V(1)N(2) O(5)V(1)N(1) O(1)V(1)N(1)
I
112.89(7) 87.60(6) 86.57(6) 108.49(7) 86.25(6)
O(5)V(1)O(1) O(5)V(1)N(2) O(1)V(1)N(2) O(2)V(1)N(1) N(2)V(1)N(1)
II
Bond d, A Bond d, A
V(1)-O(1) V(1)-O(5) V(1)-N(2) Zn(1)-O(1) Zn(1)-N(1) 1.9326(14) 1.5939(15) 2.0563(17) I 1.989(7) 2.081(9) V(1)-O(2) V(1)-N(1) I Zn(1)-O(3) 1.9234(14) 2.0619(17) 2.021(10)
Angle ro, deg Angle ro, deg
107.16(7) 102.35(8) 149.85(7) 138.13(6) 78.64(7)
O(1)Zn(1)O(L4) 90.0(4) O(1)Zn(1)O(3) 106.3(3)
O(1)Zn(1)O(3^) 106.3(3) O(1)Zn(1)N(U) 150.7(4)
O(3)Zn(1)N(U) 101.9(4) O(1)Zn(1)N(1) 89.5(3)
N(1)Zn(1)N(U) 77.0(6)
4 KOOP,3HHAUHOHHAH XHMH3 tom 40 № 4 2014
Table 3. Geometric parameters of hydrogen bonds for complexes I and II*
D H-A Distance, À Angle D-H—A, deg
D-H H-A D-A
O(6)-H(6wA)-O(4) O(6)-H(6wA)-O(2) O(6)-H(6wB)-O(1) O(6)-H(6wB)-O(3) 0.85(1) 0.85(1) 0.85(1) 0.85(1) I 2.29(2) 2.26(2) 2.36(3) 2.20(2) II 2.00(6) 2.32(8) 3.037(3) 2.983(2) 3.012(2) 2.984(2) 147(3) 143(3) 134(3) 153(4)
O(3)-H(3)-O(1)i O(3)—H(3)-O(2)i 0.85(1) 0.85(1) 2.756(10) 2.986(7) 147(10) 136(9)
* Symmetry code: i —1/2 + y, 1/2 + x, —1 + z.
in Table 1. Selected bond lengths and angles are given in Table 2. The O-H—O hydrogen bonds in complexes I and II are listed in Table 3.
Supplementary material for structure I and II has been deposited with the Cambridge Crystallograph-ic Data Centre (nos. 935001 (I) and 935002 (II); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam. ac.uk).
Antibacterial assay. The antibacterial activities were tested against B. subtilis, E. coll, and S. aureus using Mueller-Hinton medium. The MICs (minimum inhibitory concentrations) of the test compounds were determined by a colorimetric method using the dye MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazoli-um bromide]. A stock solution of the synthesized compound (50 ^g mL-1) in DMSO was prepared and quantities of the test compounds were incorporated in specified quantity of sterilized liquid Mueller-Hinton medium. A specified quantity of the medium containing the compound was poured into microtitration plates. A suspension of the microorganism was prepared to contain approximately 105 cfu mL-1 and applied to microtitration plates with serially diluted compounds in DMSO to be tested and incubated at 37°C for 24 h. After the MICs were visually determined on each of the microtitration plates, 50 ^L of PBS (phosphate buffered saline 0.01 mol L-1, 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 of MTT/mL was added to each well. Incubation was continued at room temperature for 4-5 h. The content of each well was removed and 100 ^L of isopro-panol containing 5% 1 mol L-1 HCl was added to ex-
Table 4. MIC values (p.g mL 1) of the tested compounds
B. subtilis E. coli S. aureus
H2L 25 50 25
I 1.56 12.5 3.13
II 3.13 12.5 6.25
Penicillin 0.78 >100 3.13
Kanamycin 0.39 6.25 1.56
tract the dye. After 12 h of incubation at room temperature, the optical density was measured with a microplate reader at 550 nm. The antibiotics kanamy-cin and penicillin were used as standard drugs. The observed MIC values are given in Table 4.
RESULTS AND DISCUSSION
Reaction of H2L with vanadyl acetylacetonate and zinc chloride, respectively, under aerobic conditions afforded mononuclear vanadium complex I and mononuclear zinc complex II. Both complexes were obtained as single crystals, stable in air and soluble in polar organic solvents, such as ethanol, methanol, DMF, and DMSO. Elemental analyses of the complexes are consistent with the general molecular formulae proposed by single crystal X-ray de
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