КООРДИНАЦИОННАЯ ХИМИЯ, 2008, том 34, № 5, с. 380-387
УДК 541.49
SYNTHESIS, SPECTRAL STUDIES OF COBALT(II) TETRATHIOCYANATO DICUPERATE(I) COMPLEXES WITH SOME ACYLHYDRAZONES AND THEIR ANTIMICROBIAL ACTIVITY
© 2008 V. P. Singh and A. Singh
Department of Chemistry, Banaras Hindu University, Varanasi 221005, India E-mail: singvp@yahoo.co.in Received March 1, 2007
Cobalt(II) complexes of the type Co[Cu(NCS)2]2 ■ L, where L is acetophenonebenzoylhydrazone (Abh), ace-tophenoneisonicotinoylhydrazone (Ainh), acetophenonesalicyloylhydrazone (Ash), acetophenoneanthra-niloylhydrazone (Aah), p-hydroxyacetophenonebenzoylhydrazone (Phabh), p-hydroxyacetophenoneisonicoti-noylhydrazone (Phainh), p-hydroxyacetophenonesalicyloylhydrazone (Phash), and p-hydroxyacetophenon-eanthraniloylhydrazone (Phaah) were synthesized and characterized by elemental analyses, molar conductance, magnetic moments, electronic and IR spectra, and X-ray diffraction studies. The complexes are insoluble in common organic solvents and are non-electrolytes. These complexes are coordinated through the >C=O and >C=N groups of the hydrazone ligands. The magnetic moments and electronic spectra suggest a spin-free octahedral geometry around Co(II). The X-ray diffraction parameters (a, b, c) for Co[Cu(SCN)2]2 ■ Ainh and Co[Cu(SCN)2]2 ■ Phabh correspond to orthorhombic and tetragonal crystal lattices, respectively. The complexes show a fair antifungal and antibacterial activity against a number of fungi and bacteria. The activity increases with increasing concentration of the compounds.
INTRODUCTION
Schiff bases containing the RC=N- group constitute an interesting class of chelating agents capable to coordinate with one or more metal ions giving mononuclear or polynuclear metal complexes, which serve as models for metalloproteins [1]. It has been suggested that monoamine oxidase enzyme inhibition occurs via metal Schiff base complex formation [2]. Copper(II) sali-cylaldehyde benzoylhydrazone [3] and 2-pyridine car-boxaldehyde-2-pyridylhydrazone [4] have been reported to produce significant inhibition of tumor growth.
Cobalt(II) complexes, besides existing in several stereochemical dispositions, interact with molecular oxygen ultimately oxidizing complexed Co(II) to Co(III). The best studied examples are cobalt(II) Schiff base complexes that take up O2 in DMF or pyridine solution [5]. Heterobimetallic complexes formed by the combination of two metal thiocyanates, Co(NCS)2 and CuSCN, with a potent acylhydrazone ligand should be more biologically active than the metal thiocyanate or the hydrazone ligand. Therefore, we report here the synthesis, characterization, electronic, and IR spectral studies, and X-ray diffraction studies of cobalt(II) tetrathiocyanatodicuperate(I) complexes with some acylhydrazones. The antifungal and antibacterial properties of the ligands and their complexes were also tested.
EXPERIMENTAL
Materials. All chemicals were of AnalaR (BDH) or equivalent grade. Isonicotinic acid hydrazide
(NC5H4NHNH2) was obtained from S.D. Fine Chemicals (Mumbai) and used after recrystallization in etha-nol. Benzoic acid hydrazide (C6H5CONHNH2), salicylic acid hydrazide (HOC6H4CONHNH2), and anthranilic acid hydrazide (H2NC6H4CONHNH2) were synthesized by the reported methods [6].
Synthesis of acetophenone acylhydrazones (L).
Acetophenone benzoyl hydrazone (C6H5C(CH3)=NN HCOC6H5, Abh), acetophenone isonicotinoyl hydrazone (C6H5C(CH3)=NNHCOC5H4N, Ainh), acetophe-none salicyloyl hydrazone (C6H5C (CH3)=NNHCO C6H4(OH), Ash), acetophenone anthraniloyl hydrazone (C6H5C(CH3)=NNHCOC6H4(NH2), Aah) were synthesized by reacting the corresponding acid hydrazides with acetophenone in a 1 : 1 molar ratio in 50 ml of eth-anol in a round-bottom flask. The reaction mixture was refluxed at 60°C for 2-4 h and then allowed to cool in a beaker, and the product was filtered off by suction on a buckner funnel. The Abh and Aah ligands were re-crystallized from hot benzene while Ash and Ainh were recrystallized from hot ethanol and dried in a desiccator over anhydrous CaCl2.
Synthesis of p-hydroxy acetophenone acylhydrazones (L). p-Hydroxy acetophenone benzoylhydrazone (C6H4(OH)C(CH3)=NNHCOC6H5, Phabh); p-hy-droxyacetophenone isonicotinoylhydrazone (C6H4 (OH)C(CH3)=NNHCOC5H4N, Phainh); p-hydroxyac-etophenone salicyloylhydrazone (C6H4(OH)C(CH3)=N NHCOC6H4(OH), Phash); p-hydroxyacetophenone anthraniloylhydrazone (C6H4(OH)C(CH3)=NNHCO C6H4(NH2), Phaah) were synthesized by reacting their
Tablel. Analytical data of the ligands
Ligand (color)
Empirical formula (formula wt.)
Melting point, °C
Contents (found/calcd), %
C
Abh (white) C15H14N2O (238) 145 74.89/75.63 5.92/5.88 11.16/11.76 65
Ainh (white) C14H13N3O (239) 162 70.10/70.29 5.50/5.44 17.32/17.57 60
Ash (white) C15H14N2O2 (254) 205 70.22/70.86 5.61/5.51 10.85/11.02 65
Aah (cream yellow) C15H15N3O (253) 175 70.72/71.15 5.81/5.93 16.41/16.60 50
Phabh (light yellow) C15H14N2O2 (254) 210 70.40/70.86 5.67/5.51 10.72/11.02 60
Phainh (light yellow) C14H13N3O2 (255) 260 65.32/65.88 5.18/5.10 16.08/16.47 55
Phash (light yellow) C15H14N2O3 (270) 240 65.95/66.67 5.26/5.18 10.32/10.37 65
Phaah (light yellow) C15H15N3O2 (269) 225 66.40/66.91 5.48/5.57 15.41/15.61 55
H
N
Yield, %
corresponding acid hydrazide with p-hydroxyace-tophenone in a 1 : 1 molar ratio in 50 ml of ethanol. The reactants were refluxed for 4-6 h in a round-bottom flask at 60°C. The crude product was filtered off after cooling, recrystallized from hot ethanol, and dried in a desiccator.
The ligands were characterized by their melting points, CHN analyses, and IR spectra (Table 1).
Synthesis of metal thiocyanates. a) Cobalt(II) thio-cyanate was prepared by dissolving Co(NO3)2 ■ 6H2O (2.90 g, 10 mmol) in 50 ml of absolute ethanol and KSCN (1.94 g, 20 mmol) in 25 ml of absolute ethanol separately. Both solutions were mixed in a beaker at room temperature. Potassium nitrate was thus formed as white solid and removed by filtration. The filtrate containing Co(NCS)2 was slowly evaporated to dryness to obtain a blue colored solid product, which was redis-solved and then purified from dry ethanol to ensure removal of water soluble KNO3.
b) Copper(I) thiocyanate was prepared according to the method [7] by dissolving CuSO4 ■ 5H2O (2.49 g, 10 mmol) in 50 ml of dilute HCl (0.05 N). The solution was treated with sulfurous acid (H2SO3) to reduce Cu2+ to Cu+ and then was treated with NH4SCN (0.77 g, 10 mmol) dissolved in 25 ml of distilled water. White CuSCN was filtered off and washed with water followed by eth-anol and finally with diethyl ether.
Synthesis of Co[Cu(SCN)2]2. The Lewis acid Co[Cu(SCN)2]2 was prepared by reacting Co(NCS)2 (1.74 g, 10 mmol) and CuSCN (2.42 g, 20 mmol) in a 1 : 2 molar ratio in a round-bottom flask containing 50 ml of dioxane and fitted with anhydrous CaCl2 guard tube. The reaction mixture was stirred continuously for 48 h on a magnetic stirrer at room temperature to complete the reaction. Bright green Lewis acid thus formed was filtered off through a closed assembly, washed with dioxane, and dried in a desiccator at room temperature.
Syntheses of Co[Cu(SCN)2]2 • L were carried out by reacting Lewis acid Co[Cu(SCN)2]2 (2.85 g, 5 mmol) separately with 5 mmol each of the ligands Abh (1.19 g), Ainh (1.20 g), Ash (1.27 g), Aah (1.26 g), Phabh (1.27 g),
Phainh (1.28 g), Phash (1.35 g), and Phaah (1.35 g) dissolved in 50 ml of dioxane in a round-bottom flask. The mixture was well stirred on a magnetic stirrer for 20-48 h at room temperature until a visible color change of the product occurs. The product was filtered off, washed with dioxane followed by diethyl ether and then dried in a desiccator at room temperature.
Analyses and physicochemical studies. For determination of the copper and cobalt contents were used method described in [7]. Carbon, hydrogen, and nitrogen contents were determined by using an Elemental Vario EL III Carlo Erba 1108 model microanalyzer. The molar conductances of 10-3 M solutions of the complexes in DMSO were measured at room temperature on a Systronic Conductivity meter model-306. Room temperature magnetic susceptibilities were determined on a Faraday balance using Hg[Co(SCN)4] as calibrant and corrected for diamagnetism [8]. IR spectra were recorded in a KBr medium on a Vector-22 spectrophotometer. Electronic spectra were recorded in DMSO solution on a Perkin Elmer Lambada-2 spectro-photometer. Powder X-ray diffraction patterns of a few complexes were recorded on an Iso Debye Flex 2002 apparatus using CuA^ radiations. The elemental analysis and physicochemical data of complexes are given in Tables 2-4.
Antifungal activity. The ligands, as well as their complexes, were screened for antifungal activity against various fungi, viz., Rizoctonia sp. and Pénicillium sp. These species were isolated from the infected organs of the host plants on a potato dextrose agar (potato 250 g + dextrose 20 g + agar 20 g) medium. The cultures of the fungi were purified by the single spore isolation technique.
The solutions with different concentrations 0.5, 1, and 1.5 mg/ml of each compound in DMSO were prepared for testing against spore germination. A drop of the solution of each concentration was kept separately on glass slides. The conidia, fungal reproducing spores (~200) lifted with the help of an inoculating needle, were mixed in each drop of each compound separately. Each treatment was replicated thrice and a parallel DMSO
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