научная статья по теме SYNTHESIS, SPECTRAL, AND BIOLOGICAL STUDIES OF SOME METAL(II) COMPLEXES WITH BENZIL SALICYLALDEHYDE ACYLDIHYDRAZONES Химия

Текст научной статьи на тему «SYNTHESIS, SPECTRAL, AND BIOLOGICAL STUDIES OF SOME METAL(II) COMPLEXES WITH BENZIL SALICYLALDEHYDE ACYLDIHYDRAZONES»

КООРДИНАЦИОННАЯ ХИМИЯ, 2008, том 34, № 4, с. 277-284

УДК 541.49

SYNTHESIS, SPECTRAL, AND BIOLOGICAL STUDIES OF SOME METAL(II) COMPLEXES WITH BENZIL SALICYLALDEHYDE

ACYLDIHYDRAZONES

© 2008 V. P. Singh1, P. Gupta1, and N. Lal2

1Chemistry Department, Faculty of Science, Banaras Hindu University, Varanasi 221005, India 2Institute of Life Sciences, Chhatrapati Shahu Ji Maharaj University, Kanpur 208024, India

E-mail: singvp@yahoo.co.in Received November 7, 2006

Complexes of the general composition [M(Bsodh)]Cl and [M(Bsmdh)]Cl, where M = Co(II), Ni(II), Cu(II), Zn(II,) and Cd(II) (HBsodh = benzil salicylaldehyde oxalic acid dihydrazone and HBsmdh = benzil salicylal-dehyde malonic acid dihydrazone) were synthesized and characterized by elemental analyses, molar conductance, magnetic moments, electronic, ESR, infrared spectra, and X-ray diffraction studies. The complexes are stable solids insoluble in common organic solvents and 1 : 1 electrolytes. The magnetic moments and electronic spectra reveal a square-planar geometry for [M(Bsodh)]Cl and a six-coordinate octahedral geometry for [M(Bsmdh)]Cl. The HBsodh ligand bonds to the metal ion via one >C=O, two >C=N-, and one deprotonated phenolate group, whereas HBsmdh bonds through three >C=O, two >C=N-, and one phenolate group. The lattice parameters for [Co(Bsodh)]Cl and [Ni(Bsmdh)]Cl correspond to tetragonal and orthorhombic crystal lattices, respectively. ESR spectral data indicate the presence of an unpaired electron in d 2 2 of the Cu2+ ion.

x — y

The ligands, as well as their metal complexes, show significant antibacterial activity against Bacillus subtilis and Pseudomonas fluorescens.

INTRODUCTION

Schiff base transition metal complexes have been studied extensively and have applications in various fields, viz., in radioimaging and radiotherapy [1], in sweetening of hydrocarbon fractions [2], in the formation of electroluminescent devices [3], as heat stabilizers for polyamides, etc. [4]. Such complexes have been implicated in the transport of active substances through membranes [5]. Schiff base complexes containing nitrogen and oxygen as donor atoms play an important role in biological systems and represent models for metalloproteins and metalloenzymes that catalyze the reduction of nitrogen and oxygen [6]. These complexes have been reported to show significant antifungal and antibacterial activities [7, 8].

Acyldihydrazines (or organic acid dihydrazides), such as oxalic acid dihydrazide, (CONHNH2)2, malonic acid dihydrazide, CH2(CONHNH2)2, etc. having two terminal amino groups can react either with two molecules of monoketo group containing compounds [9], one molecule of diketo compounds [10], or one molecule each of two different keto group containing compounds under suitable conditions. The acyldihydra-zones thus obtained have two C=N groups in addition to several other potential donor sites for bonding with metal ions [11-13]. In the absence of an adequate studies on such ligands, viz., benzil salicylaldehyde oxalic acid dihydrazone (HBsodh) and benzil salicylaldehyde

malonic acid dihydrazone (HBsmdh), their complexes with some bivalent transition metal ions (Co2+, Ni2+, Cu2+, Zn2+, and Cd2+) were synthesized, characterized and discussed in the present study:

ç-^nnhc-(ch2)x-çn№c-/ \

O O O )-'

HO

where x = 0 for HBsodh and 1 for HBsmdh.

EXPERIMENTAL

Material. All the chemicals used were of BDH (AnalaR) or equivalent grade. The precursor acyldihy-drazines, oxalic acid dihydrazide (Odh), (CONHNH2)2 and malonic acid dihydrazide (Mdh), CH2(CONHNH2)2 were prepared as by the procedure given in the literature [14] and were characterized by their melting points, Odh m.p. 232°C (lit.: 232°C); Mdh m.p. 150°C (lit.: 152°C).

Synthesis of the ligands. For the synthesis of HB sodh, C6H5COC(C6H5)=NNHCOCONHN=

CHC6H4OH, and HBsmdh, C6H5COC(C6H5)= NNHCOCH2CONHN=CHC6H4OH, benzil (10 mmol, 2.1 g) and salicylaldehyde (10 mmol, 1.22 ml) were taken in a beaker containing 50 ml of ethanol. The

above solution mixture was reacted separately with an aqueous solution (50 ml) of oxalic acid dihydrazide (10 mmol, 1.18 g) or malonic acid dihydrazide (10 mmol, 1.32 g), respectively, and was continuously stirred for ~2 h on a magnetic stirrer at room temperature. The product was filtered off by suction and purified by washing several times with hot water and then with eth-anol. The pure ligands were dried in a desiccator over anhydrous CaCl2.

The ligands were characterized by elemental analyses (C, H, N), melting points, and infrared spectra.

Synthesis of the complexes. Metal complexes of HBsodh and HBsmdh were prepared by reacting of 50 ml aqueous solutions containing 5 mmol of CoCl2 ■ 6H2O (1.19 g) (or NiCl2 ■ 6H2O (1.19 g), CuCl2 ■ 2H2O (0.85 g), ZnCl2 (0.68 g), and CdCl2 ■ 2.5H2O (1.14 g)) with 50 ml of aqueous ethanolic solutions (v/v, 1 : 1), 5 mmol of HBsodh (2.07 g) or HBsmdh (2.14 g) in the 1 : 1 (M : L) molar ratio in a RB flask. The Co(II) and Ni(II) complexes were formed by refluxing the reaction mixture solutions for 3-4 h with shaking at regular intervals. However, Cu(II), Zi(II), and Cd(II) complexes were obtained by stirring their corresponding solutions for 1, 2, and 3 h on a magnetic stirrer, respectively. The products were filtered by suction and dried in a desiccator over anhydrous CaCl2 at room temperature after washing. Since these complexes were insoluble and non-crystallizable, and they were purified by washing thoroughly with water and ethanol to remove unreacted metal chlorides or ligands.

Analyses and instrumentation. Metal contents were determined gravimetrically by a literature procedure [15] after digesting the organic matter with aqua regia and evaporating the residue to dryness with concentrated sulfuric acid. The chloride content was analysed gravimetrically as silver chloride. C, H, N data were determined on an Elementar Vario EL model elemental analyzer.

The molar conductance of 10-3 M solutions of the complexes in DMF were measured at room temperature on a Systronic conductivitymeter (model-306). Room temperature magnetic susceptibilities of the complexes were determined on a Faraday balance using Hg[Co(SCN)4] as calibrant and corrected for dia-magnetism [16]. IR spectra of the ligands and their metal complexes were recorded in a KBr medium in the 4000-500 cm-1 range on a Vertex 70 (Bruker) spectro-photometer. Electronic spectra were recorded in DMF on a Cintra 10 spectrophotometer. The X-band ESR spectra of the Cu(II) complexes were recorded on an EMX 1444 EPR spectrometer at liquid-nitrogen temperature in a DMF solution and at room temperature (300 K) in the solid state. Powder X-ray diffraction patterns were recorded on an Iso Debye Flex 2002 apparatus using Cu^a radiations.

The analytical and physicochemical data are given in Tables 1-5.

Antibacterial activity. The antibacterial activity of the ligands and their complexes was studied against Pseudomonas fluorescence (Gram -ve) and Bacillus subtilis (Gram +ve) bacteria. Each of the compounds was dissolved in DMSO and solutions with the concentration 2.0 and 1.0 mg/ml were prepared separately. Paper discs of whatman filter paper (no. 42) of uniform diameter were cut and sterilized in an autoclave. The paper disc soaked in the complex solution of the desired concentration was placed aseptically in the Petri dishes containing nutrient agar media (agar 15 g + beef extract 3 g + peptone 5 g) seeded with Bacillus and Pseudomonas sp. bacteria separately. The Petri dishes were incubated at 32°C and the inhibition zones were recorded after 24 h of incubation. Each treatment was replicated for 9 times.

A common standard antibiotic Ampicillin was also screened for antibacterial activity in the same solvent and at the same concentration. The percent activity index data for the metal complexes were calculated as follows:

%Activity index =

Zo ne 0 f i nhibitio n b y te st c ompound (di ameter) Zone of inhibition by standart (diameter)

x 100.

RESULTS AND DISCUSSION

It appears from the analytical data of the complexes (Table 1) that both the ligands HBsodh and HBsmdh undergo deprotonation of their phenolic proton during complexation. The ligands react with metal ions in 1 : 1 (M : L) molar ratio to form the complexes of the general compositions [M(Bsodh)]Cl and [M(Bsmdh)]Cl. The reactions are shown below:

MCl2 ■ xH2O + HBsodh-or

HBsmdh

■ [M(Bsodh)]Cl + HCl + xH2O, or

[M(Bsmdh)]Cl

where M = Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); x = 0-6.

The metal complexes are air stable solid powders, insoluble in water and common organic solvents, such as methanol, ethanol, chloroform, carbon tetrachloride, diethyl ether, ethyl acetate, and benzene but are fairly soluble in DMF and DMSO. The complexes either melt or decompose in the temperature range 188-266°C except [Cu(Bsodh)]Cl, which does not melt up to 300°C.

The Co(II) complexes are light orange and light brown, Ni(II) complexes are light yellow and greenish yellow, Cu(II) complexes are yellow-green and green, whereas, Zn(II) and Cd(II) complexes are yellow to light yellow in color. The molar conductance values of 10-3 M solution of the complexes in DMF at room temperature fall in the range 69.4-81.5 Ohm-1 mol-1 cm2.

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Table 1. Analytical data of the ligands and their metal complexes

Compound Empirical formula M.p./D.p., °C Contents (found/calcd), % Yield, % Molar conductance,

(colour) (formula weight) Metal CI C H N Ohnr1 mor1 cm2 in DMF

HBsodh (light yellow) C23H18N4O4 (414) 208 65.70/66.67 4.18/4.35 12.32/13.52 85

HBsmdh (cream yellow) C24H20N4O4 (428) 178 67.22/67.29 4.52/4.67 12.80/13.08 80

[Co(Bsodh)]Cl (light brown) C23H17N4O4CIC0 (507.5) 222 11.50/11.62 6.78/7.00 54.19/54.38 3.32/3.35 10.97/11.03 82 70.6

[Ni(Bsodh)]Cl (light yellow) C23HlvN404ClNi (507.5) 230 11.40/11.62 7.00/7.00 54.28/54.38 3.31/3.35 10.93/11.03 80 78.2

[Cu(Bsodh)]Cl (yellow-green

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