Synthesis, Characterization and Antimicrobial Study of Some Transition Metal Complexes with Aldimine

Abstract

Aldimine ligand 2-Hydroxy-4,5- diiodo-benzylidene-4-hydroxy-aniline (L) and its complexes with Cu (II), Ni (II), Co (II) and Zn (II) were prepared and characterized by analytical, spectroscopic (IR, UV-Vis) techniques, thermal study, electrical conductivity and magnetic measurements. The results indicate that the ligand coordinate through azomithine nitrogen and oxygen of enolic group. The complexes were further screened for antimicrobial activity.

Introduction

  I. INTRODUCTION

Aldimine are important class of ligand in coordination chemistry and their complex formation ability containing different donor atom is widely reported.    The chemistry of transition metal complexes containing heterocyclic donor continues to be of interest on account of their biological importance1. The aldimine metal complexes show antimicrobial2, fungicidal3 anti-cancer4 and anti-inflammatory activity5.Thus the present study describe synthesis, characterization and antimicrobial studies of some aldimine transition metal complexes.

A. Experimental

The ligand 2-Hydroxy-4,5- diiodo-benzylidene-4-hydroxy-aniline (L) has been characterized by infrared spectral studies. The complex characterized by infrared spectral studies, electronic spectral studies, magnetic moment, thermal analysis and conductivity measurement. The antimicrobial activity of the investigated compound was tested by the paper diffusion method.

B. Synthesis of Aldimine

The aldimine was synthesized by reported procedure6. To the solution of 2-hydroxy-4, 5-diiodobenzyldehyde 0.373 gm (0.001 mole) in 25 ml ethanol and 0.109 gm (0.001 mol) p-amino phenol in 25 ml ethanol was added. The solution was refluxed for 5-6 hrs. The solution was monitored on TLC, on completion of reaction the solution was concentrated, cooled and poured in water the separated solid was filtered, washed with water and recrystallized from ethyl alcohol and dried over calcium chloride in vacuum. The composition and yield of aldimine have shown in table no 1.

C. Synthesis of Metal Complexes

The metal complexes of Cu (II), Ni (II), Co (II) and Zn (II) with ligand were prepared by refluxing the ethanolic solution of metal nitrate and ligand in 1:2 molar ratios. The pH of solution was adjusted by alcoholic ammonia.

Ligand (0.02 mole) in slight excess was taken in a round bottom flask containing 30 ml anhydrous ethanol and refluxed for few minutes with constant stirring to ensure complete dissolution; a solution of the appropriate metal nitrate (0.01 M) in 20 ml of anhydrous ethanol was then added drop by drop with constant-stirring in the hot solution of ligand. The content was refluxed five hours. After cooling, the pH of the mixture was maintained by the addition of alcoholic ammonia solution. The resultant precipitate was digested for one hour. The precipitate was filtered, washed with hot ethanol and dried in vacuum desiccators over anhydrous granular calcium chloride. The composition and yield of metal complexes have shown in table no 1.

II. RESULT AND DISCUSSION

The metal complexes are colored and stable to air and moisture. They are insoluble in water, sparingly soluble in benzene, chloroform, carbon tetrachloride etc. and completely soluble in dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO). Elemental analysis suggests that the complex have 1:2(metal-ligand) stoichiometry.

The conductivity value in DMF (1 x 10-3M) reveals their electrolyte nature 7,8. Based on elementary chemical analysis the formula, ML2(H2O)2 (NO3)2 were suggested for all compounds. In IR spectrum of ligand, shows band at 2823.60 cm-1 assigned to –OH stretching, the lowering of normal free –OH stretching frequency from 3600- 3500   cm-1 to above value is expected due to the strong intramolecular hydrogen bonding.9  A  bond at 1620.10 cm-1 assigned to azomethine (C=N) stretching vibration. A bond at 1274.90 cm-1 is assigned to enolic C-O stretching frequency.

Table 1: Analytical data of ligand and metal complexes

In the spectra of Cu(II) complexes the band at 2823.60 cm-1 disappears. The band at 1620.10 cm-1 is shifts to lower frequency (1615.10 cm-1), indicating the co-ordination of azomethine nitrogen to metal atom. In spectra of complex the broad band at 3354.73 cm-1, indicating the presence of coordinated water. The bands at 1274.90 cm-1 show upward shift (1285.90 cm-1 ) suggest the bonding of enolic oxygen of aldimine base with metal during complexation10,11 , further confirmed by a new band. The new bands at 527.18 cm-1 and 498.77 cm-1 in the spectra of complex are assigned to stretching vibration of M-N and M-O bands respectively12.

Table-2: IR frequency (cm-1) of ligand and complexes

The UV-Visible spectra of copper complexes of ligand exhibit bands at 15576 cm-1, 27932 cm-1 attributed to 3Eg?2T2g and charge transfer transition which indicate distorted octahedral geometry of Cu (II) complexes, which further supported by μeff value 1.90 B.M.13.

The ligand field parameter values (Dq and LFSE) observed at 15576 cm-1 and 44.47 kcal mole-1 respectively and these are in good agreement with the distorted octahedral Cu (II) complexes.

The electronic spectra of Ni (II) complex exhibit bands in the three regions as 9587 cm-1 15948 cm-1 and 24213 cm-1. This pattern of absorption may be assigned to transition 3A2g?3T2g(F), 3A2g?3T1g (F) and 3A2g?T1g (P) respectively. This may be assigned to characteristic three spin allowed transition of octahedral complexes14, further supported by μeff value 3.39 B.M.

The reduction of B values for the Ni(II) complexes (760.00 cm-1)  as compared to the free ion value for Ni(II) ion (1030 cm-1) reveals complex formation. The Nephelauxetic ratio (β) obtained are less than unity (0.737) in this case suggesting considerable amount of covalent character of the metal ligand bonds.  The LFSE value (27.37 Kcal mole-1) indicate considerable stability of Ni(II) complexes.  The energy ratio ν2/ ν1 (1.663) being close to reported values (1.6-1.82) as well as the 10Dq (9587cm-1) and percentage of β found (35.68) indicate that the Ni (II) complex is in octahedral geometry.

The electronic spectra of Co (II) complex exhibit bonds at 9451 cm-1 , 18281 cm-1 and 22123 cm-1. These bands may be assigned to to 4T1g(F)?4T2g , 4T1g(F)?4A2g, (F) and 4T1g(F)?4T1g, (p)  respectively, suggesting a high spin octahedral geometry around the cobalt ion. Octahedral geometry around  cobalt ion15 further supported by μeff value 4.73B.M.

The reduction in B values for all the Co(II) complexes (803.40 cm-1) as compared to the free ion value for Co(II) ion (971 cm-1) reveals complexes formation thereby favoring the orbital overlap and delocalization of d orbital.  The Nephelauxetic ratio (β) in each case is less than unity (0.827) and their %β values (20.91 %) indicate partial covalent character in metal ligand bond. The LFSE value (25.21 Kcal mole-1) indicates considerable stability of Co (II) complexes.

The electronic spectra of Zn (II) complex exhibits bands at 27777 cm-1 attributed to charge transfer transition suggesting an octahedral environment16. This complex is diamagnetic in nature.

The simultaneous use of TG and DTA is made in the present study of metal complexes with a view to understand stoichiometry, thermal stability, the presence and nature of water molecules. The water in inorganic compounds may be classified as lattice water and coordinated water. There is however, no definite border line between the two. The former term denotes water molecules trapped in the crystalline lattice, either by weak bonds to the anion or by weak ionic bonds to the metal or by both, where as the latter denotes water molecules bonded to the metal through partial covalent bonds or coordinate bonds.  According to Freman and Carrol18 the water eliminated below 150 °C can be considered as lattice water and above 150 °C as water coordinated to metal ion19.

A close look at TG curve (Figure-3) of Cu(II) complexes of show that, the complexes stable up to 160 °C. Thereafter, the complexes start decompressing gradually. The percentage weight loss is about 3.40% in complex (cal 3.5%).  This decomposition begins at 160 °C and continues up to 240 °C.  The weight corresponds to two mole of coordinated water molecule. The loss of coordinated water molecules in Cu(II) complex is a single step process, indicated by endothermic peak in DTA curve. After this, Cu(II) complexes show sharp decrease in weight, indicating decomposition of complexes, further confirmed by endothermic nature of peaks obtained in DTA curve, organic part content of meal complex is removed during this loss and decomposition continues up to the temperature 800 °C leading to the formation of stable residue of metal oxide i.e. CuO.

The simultaneous use of TG and DTA show that the metal complexes are thermally quite stable.  Thermograms of all the complexes indicate the presence of coordinated water molecules. X-Ray powder pattern investigation suggests that all the complexes are crystalline in nature.

A. Antimicrobial Activity

The ligand and their metal complexes were tested for antibacterial activity Mueller Hinton agar was used for testing the susceptibility of microorganism by well diffusion method, using DMSO as solvent, at a concentration of 0.01 M against gram positive (staphylococcus aureus) and gram negative (Escherichia coli) bacteria.

The zones inhibition against the growth of microorganisms was determined at the end of incubation period 24 h at 37oC and the results are presented in table 3. It was found that the metal complexes are more active than the free ligand.

III. ACKNOWLEDGMENT

The author is thankful to Dr. W N. Jadhav, Principal Sharda Mahavidyalaya Parbhani, Dr. B. C. Khade, Dr. S.R. Bhusare, DSM College, Parbhani, Dr. B. R. Patil, Sharda Mahavidyalaya , Parbhani for their valuable guidance. Also thanks to Dr S. L. Sadawrte, Principal, DSM College, Jintur, for providing the necessary facilities.

Table 3: Antimicrobial activities of Schiff bases and their complexes

References

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