INTRODUCTION:

Coordination compounds exhibit different characteristic properties, which depends on the metal ion to which they are bound, the nature of the metal as well as the type of ligand etc. These metal complexes have found extensive application in various fields of human interest. Thiourea and salicylaldehyde are capable to form complexes with transition metal ions in the form of Schiff base. The complexes of Ni(II), Fe(II), Hg(II), Zn(II) and Cd(II), Schiff base have been synthesized. The M(II) Schiff base complexes also have been prepared from Salicylaldehyde and O-aminobenzoic acid. Metal selected for the preparation of complexes was Cu, Ni, Fe and Zn. They showed that the Ni complex of Schiff base showed best antibacterial activity^1-3. Mixed ligand complexes of Ni,Cu,and Zn(II) with 5-chloro(or bromo) salicylaldehyde and hydroxyl aromatic aldehydes or ketons have been synthesized and characterized these complexes by conductance, TLC, thermalanalysis, magnetic moments, IR, ¹H NMR and electronic spectral studies^4-7. Synthesis, characterization and antimicrobial activity of cobalt(II) and nickel(II) complexes of acetyl derivatives of urea and thiourea have been synthesized Metal Schiff base complexes are monodentate and bind to the central metal atom through the oxygen and sulphur donor atoms^8-10.

Homogeneous catalytic hydrogenation of organic compounds using orthometallated Schiff base complexes of palladium (II) have been carried out. Catalytic activites of various dinuclear orthopalladated complexes with differently C,N- substituted Schiff base ligand^11-12also have been carried. As all these work suggest that Schiff base complexes have a large number of roles as drugs, catalysts etc. In the present work, complexes of Ni(II), Fe(II), Hg(II), Zn(II) and Cd(II) with Schiff base derived from Salicylaldehyde and Thiourea, have been synthesized, characterized by IR,UV,NMR and Elemental analysis. The antibacterial activity of the prepared Schiff base complex derived from Salicylaldehyde and Thiourea have been investigated.

MATERIALS AND METHODS:

Metal salts Nickel Nitrate, Ferrous Sulphate, Zinc oxide and Cadmium acetate Salicylaldehyde (AR), Thiourea (AR), Ethanol were purchased from Sd. Fine Chemical Ltd. Boisar. Mercury(II)chloride HgCl₂ (AR) is obtained from E. Merck Ltd., Mumbai. The Antibacterial activity of synthesized Schiff base metal complexes was determined by Disc diffusion method. For the synthesis of Schiff base 20ml of ethanolic solution of salicylaldehyde (2.094ml; 0.01M) and the same volume of ethanolic solution of thiourea (0.76gram; 0.01 M) were mixed. The mixture was stirred for 4-5 hours in a mechanical stirrer. This solution was evaporated to remove the solvent. The product after filtration was washed several times with ethanol and recrystallized from hot ethanol and dried.

For each metal complex, different metal salt solution were prepared. The compounds used for the synthesis of the Ni (II), Fe (II), Hg (II), Zn (II) and Cd (II ) complexes were Nickel nitrate, Ferrous sulphate, Mercury chloride, Zinc Oxide and Cadmium Acetate, respectively. The Schiff base (0.01M; 0.0568 gram) in 20 ml of ethanol and the same volume of ethanolic solution of M (II) salt (0.01M) were mixed and stirred in the magnetic stirrer for 4-5 hours. It was kept in the water bath for the evaporation of excess of ethanol. It was then cooled. The precipitate formed was filtered and washed several time with hot ethanol to remove excess metal ion. The precipitate was then dried and stored in a desiccator over anhydrous CaCl₂ under vacuum.

RESULTS AND DISCUSSIONS:

Metal ions play a vital role in a number of different biological processes through co-enzymatic system. The interaction of these ion with biologically active ligand, for instance in drugs, is subject of great interest. Some biologically active compounds act via chelation, but for most of them little is known about how metal coordination influences their activity.

The yield and colour of samples are given in Table.1.

TABLE – 1 : Yield and the colour of the complexes

S. No	Compound	Colour	% Yield
1.	S.T.1	Green	85.6
2.	S.T.2	Sandal	94.3
3.	S.T.3	Silver	96.7
4.	S.T.4	White	88.4
5.	S.T.5	Yellow	73.1

S.T.1 à Nickel complex, S.T.2 à Ferrous complex,

S.T.3 à Mercury complex, S.T.4 à Zinc complex and

S.T.5 à Cadmium complex.

The percentage of C, H, N, S and Metal obtained from the Elemental analyzer are compared with the percentages calculated using the assumed structure of 1:1(M:L) complex. The proximity of the values suggests that the ligand forms 1:1 complex with the metal ions. The results are tabulated in Table-2.

The results of the IR Spectrum of the complexes are collectively given in Table.3.From the FT-IR Spectral studies, we observed that Schiff base shows bands at 3152-3300cm^-1 which is due to the intramolecular bonding involving hydrogen of the phenolic group and nitrogen atom of amine group. This band disappears in complexes indicating the replacement of phenolic hydrogen by metal ion. The γ_C=Nband appears at 1533-1600 cm^-1 in the metal complexes (except Ferrous complex) as compared to that at 1612 cm^-1in Schiff base. This decrease indicates the coordination of Nitrogen of Azomethine group with the metal ion.

The γ_C=Sband appears at 715-617 cm^-1 in the metal complexes as compared to that at 731 cm^-1 in Schiff base. This decrease indicates the coordination of Sulphur of thiol group with the metal ion.

The γ_M-N, γ_M-O, γ_M-S bands appears at 500-619 cm^-1, 423-490 cm^-1, 400-423 cm^-1 respectively in the metal complexes. This arises due to the formation of M-O, M-N, and M-S bonds in the complexes (Nickel, Mercury, Zinc and Cadmium). From this we confirm that Oxygen, Nitrogen and Sulphur atom in the Ligand are coordinated to metal ion.

From the UV-Vis Spectral studies it was concluded that Ni (II) complex have the octahedral geometry, and Fe (II) complex have the tetrahedral geometry. The UV-Vis Analytical data for the complexes and Ligand was given in Table.4.The other three complexes like Hg (II), Zn (II) and Cd (II) have d¹⁰ configurations. So there is no d-d transitions are possible.

The ¹H NMR Spactra of the ligand show multiplet at 6-7.8 ppm which is due to aromatic protons. Phenolic –OH proton appears as singlet at 10.05-10.81ppm. Ar-CH=N proton gives singlet at 3.320-3.452ppm. Proton from water molecule from DMSO form singlet at 2.55ppm. These peaks correspond to the different kinds of protons present in the ligand. In ¹H NMR spectra of the Zinc complex the signal at 6-7.8 corresponds to the aromatic proton. The proton from water molecule in DMSO shows the downfield shift at 2.6-2.7ppm. The proton from Ar-CH=N show downfield shift at 3.520-3.652 ppm. These peaks correspond to the different kinds of protons present in the Zinc complex. These shifts arise due to the coordination of metal ion towards the ligand. All the spectral data gave evidence for the structure of ligand as well as the complexes.

With the discovery of more new diseases, the need for potential antibiotics is also increasing. So, we carried out the analysis of antibiotic activity of the complexes against the different types of bacteria, Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Ceftazidime, Salmonella typhi “H”, Klebsiella Aerogenes, Micrococci, Proteus vulgaris, Bacillus subtilis. From this analysis we found that some of the complex were found to possess antibacterial activity for E. coli, Bacillus subtilis, Klebsiella aerogenes, Staphylococcus, and Pseudomonas aeruginosa. Mercury complex show inhibition Zone of 3 mm for the Bacillus stubtilis, and 1mm for the E. Coli bacteria. Zinc Complex show inhibition zone of 3mm for the Pseudomonas areuginosa, and inhibit 1mm of growth for the E. coli, Bacillus subtilis, Klebsiella aerogenes, Staphylococcus bacteria. Cadmium complex show inhibition Zone of 1mm for the Staphylococcus bacteria.

The results are tabulated in the Table: 5. Comparison of antibacterial activity of the different metal complexes against various bacteria can be obtained from the graph given in Fig.1

Table-2 Elemental Analytical data of Schiff base and its M(II)complexes

Compound	Found (Calc)%					Melting point ^oC
Compound	M	C	H	N	S	Melting point ^oC
Ligand	-----	62.14 (63.36)	4.11 (4.25)	9.62 (9.85)	11.21 (11.28)	182-185
Ni (II)complex	16.24 (16.26)	49.89 (49.90)	3.89 (3.91)	7.70 (7.76)	8.86 (8.88)	295-298
Fe (II)complex	15.52 (15.59)	50.26 (50.30)	3.87 (3.94)	7.80 (7.82)	8.91 (8.95)	223-227
Hg (II)complex	39.84 (39.88)	35.78 (35.82)	2.79 (2.81)	5.52 (5.57)	6.32 (6.38)	292
Zn (II)complex	17.76 (17.78)	48.91 (48.99)	3.80 (3.84)	7.59 (7.62)	8.71 (8.72)	253-259
Cd (II)complex	27.09 (27.10)	43.34 (43.44)	3.34 (3.40)	6.72 (6.75)	7.69 (7.73)	241-247

Table: 3. Comparison of IR- Spectra of M(II) Complexes

Complex	Free -OH cm^-1	-OH Stretching cm^-1	-C=N cm^-1	-C=S cm^-1	M-N cm^-1	M-O cm^-1	M-S cm^-1
Ligand	----	3152-3300	1612	731	---	---	----
Ni (II) Schiff base Complex	3450	1373	1533- 1600	715	556	423	401
Fe (II) Schiff base Complex	3446	1350-1400	1627	617	586	456	412
Hg (II) Schiff base Complex	3100-3350	1398	1436	713	547	459	412
Zn (II) Schiff base Complex	3250-3450	1350-1378	1600	713.6	510	440	409
Cd (II) Schiff base Complex	3300	1355	1541	715	619	478	418

Table.4. UV-Vis Analytical data for the Ligand and Metal complexes

Compound	Solvent	Absorption(nm)	Band assignment	Geometry
L	Ethanol	260	INCT	------
Ni(II) Schiff base complex	Ethanol	268 713	INCT ³A_2gà³T_1g	Octahedral
Fe(II) Schiff Base complex	Ethanol	220 562	INCT ⁵T_2gà⁵E_g	Squareplanar

Table.5. Analysis of Antibacterial Activity of metal Complexes

Bacteria	Zone of Inhibition(mm)
Bacteria	ST1	ST2	ST3	ST4	ST5
Pseudomonas sp	----	----	----	3	----
Klebsiella sp	----	----	----	1	----
Bacillus sp	----	----	3	1	---
Staphyloccous	----	----	----	1	1
E. Coli	---	----	1	1	----
Micrococcus	----	----	----	----	----
Proteus sp	----	----	----	----	----
Pseudomonas fluorescence	----	---	----	----	----
Salmonella enterica	----	----	----	----	----

Fig.1

Based on the spectral data the following structure has been proposed. The predicted structure of the metal complex is given below:

M = Ni (II), Hg (II), Zn (II), Cd (II).

M=Fe (II).

CONCLUSION:

Schiff base transition metal complexes plays an important role in medicinal field. So, we have prepared the transition metal complexes of the metal ions Ni (II), Fe (II), Hg (II), Zn (II) and Cd (II), using the Schiff base derived from Salicylaldehyde and Thiourea. The Schiff base was first prepared by condensing Salicylaldehyde (2) and Thiourea (1). Using this as the ligand, the Schiff base metal complexes were prepared with Ni (II), Fe (II), Hg (II) and Zn (II) and Cd (II) as metal ions. The structure of the ligand was confirmed by IR, UV-Vis, ¹H NMR Spectra. The shift in the spectral bands of the ligands upon complexation was also confirmed by taking the Spectra of complexes. Using this we proposed the possible common structures for the complexes. To assess the antibacterial ability of the metal complexes, we determined the antibacterial activity of Schiff base transition metal complexes against the bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Ceftazidime, Salmonella typhi “H”, Klebsiella aerogenes, Micrococci, Proteus vulgaris, Bacillus subtilis) by finding out their Zone of Inhibition using Disc Diffusion Method. We have observed antibacterial activity of 3mm in both Zinc and Mercury complexes against Bacillus sp and Pseudomonas sp. Therefore both of these transition metal complexes can be used in Medicinal field.

SUMMARY:

A new polydentate Schiff base ligand was prepared by the condensation of Thiourea and Salicylaldehyde (1:2). The ligand has been characterized by Elemental Analysis, IR, UV-Vis, ¹H NMR. Metal complexes of Ni (II), Fe (II), Hg (II), Zn (II) and Cd (II) ions were synthesized and characterized by the usual spectral and analytical techniques. The data show that they have composition of ML. Where M=Ni (II), Fe (II), Hg (II), Zn (II) and Cd (II). The UV-Vis, ¹H NMR, IR spectral datas suggests that all complexes have octahedral geometry (except Fe (II)). The antibacterial activities of the compounds are tested in vitro against ten bacteria by the disc diffusion method. The zone inhibition property of microorganisms is much larger for metal complexes than the ligand.

REFERENCE:

1. Rajeev Johari, et al. Journal of Indian Council of Chemistry. 2009: 26: 23-27.

2. Prasad R.N, Mithlesh Agarwal and Ramesh George. Journal of Indian Chemical Society. 2005:82: 445-447.

3. Joshua A Obaleye and Chike L Orjiekwe. Journal of Indian Chemistry. 1995: 34A: 310-312.

4. Deb K Mukherjee, Biman K Palit and Chitta R Saha. Indian Journal of Chemistry. 1992: 31A:243-250.

5. Patel R.N., V.L N Gundle and D K Patel. Indian Journal of Chemistry. 2008: 47A:353-360.

6. Singh B. and Preeti Sahai. Journal of Indian Chemical Society. 1995: 34A:306-309.

7. Prasad R.N. and Anjali Agarwal. Journal of Indian Chemical Society. 2006: 83: 75-77.

8. More P.G., Muthal B.N. and Lawand A.S. Journal of Indian Chemical Society. 2006: 83:36-38.

9. Psrithri R.K., Patel R.K and Patel R.N. Journal of Indian Chemical Society. 1999: 76: 258-259.

10. Shashidhara G.M. and Goudar. T.R. Journal of Indian Chemical Society. 2001: 78: 360-361.

11. Yapas Ghosh and Bipul Mondal. Indian Journal of Chemistry. 2008: 47A:361-368.

12. Baiu S.H. Asian Journal of Chemistry. 2009: 21: 5-10.

Received on 23.07.2010 Modified on 03.08.2010

Asian J. Research Chem. 4(1): January 2011; Page 80-83

INTRODUCTION:

Table-2 Elemental Analytical data of Schiff base and its M(II)complexes

Ligand

Compound

Bacteria