Synthesis and Characterization of Mn ( II ) , Co ( II ) , Ni ( II ) , Cu ( II ) , Zn ( II ) , and Hg ( II ) Complexes with [ ( N-( N-benzilidin aminoethyl ) Iodomethylene Dithiocarbamate

A new series of transition metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Hg(II), with Schiff base (L) (N-(N-benzilidine aminoethyl) iodomethylene dithiocarbamate) is derived from (2aminoethyldithiocarbamato -iodomethane) and benzoyl, by (1:2) metal to ligand molar ratio. The complexes were characterized by metal analysis, magnetic susceptibility, molar conductance and IR, UV-Vis, spectral studies. The data showed that these complexes have the composition of [ML2Cl2] type. The UV-Vis spectral and magnetic susceptibility of the complexes suggest an octahedral geometry around each central metal ion.


INTRODUCTION
The Schiff bases and their metal complexes have more importance recently (Mobinlkhaledi et al., 2010 ; Saritha et al., 2006) because of their variety of applications in many fields: biological, inorganic and analytical chemistry (Omprakash et al., 2010;Singh et al., 2007).They have been found to possess the pharmacological activities such as antimalarial (Li et al., 2003), anticancer (Villar et al., 2004) antibacterial (Venugopal et al., 2008), antifungal (Pandey et al., 2003), antitubercular (Kathikeyan et al., 2006) and antimicrobial (Wadher et al., 2009).Schiff base ligands are able to coordinate with different metal ions and to stabilize them in various oxidation states (Chandra and Gupta, 2005;Fabbrizzi, 2010;Fry, 1997).The Schiff base complexes have been used in catalytic reactions (Mobinlkhaledi et al., 2010).Furthermore, Schiff bases have often been used as chelating ligands in the field of coordination chemistry and their metal complexes are of great interest for many years.It is well known that N, O and S atoms play a key role in the coordination of metals at the active sites of numerous metallobiomolecules (Singh et al., 2007).The aim of the present study was to prepare and characterize a new Schiff base ligand [N-(N-benzilidine aminoethyl) iodomethylene dithiocarbamato] derived from 2-aminoethyldithiocarbamatoiodo methane with benzoyl, and their complexes with Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Hg(II), (Fig. 1).

EXPERIMENTAL Material and Measurements
All chemicals were of reagent grade and used as supplied without further purification.Infrared absorption spectra were recorded on FTIR spectrophotometer Tensor 27, Brucker 2003 in the 400-4000cm -1 range using KBr discs.Electronic spectra were recorded by using a Shimadzu UV-Vis-Spectrophotometer UV-1650 for 10 -3 M solution of the compounds in dimethylformamide (DMF) at 25 °C with 1 cm quartz cell.Conductivity measurements were made on 10 -3 M solutions of the complexes in DMF at 25 °C using conductivity measuring apparatus model PCM 3 , Jenway.The metal contents of the complexes were determined using Shimadzu AA670 Atomic Absorption Spectrophotometer, after digestion with concentrated nitric acid.The magnetic susceptibility measurements were made at 25 °C by the Faraday method on the solid in a pyrex tube using Bruker BM6 instrument.

Preparation of 2-aminoethyldithiocarbamato iodo methane
The ligand was prepared by the addition of (0.1mol, 6.68ml) of ethylenediamine dropwise to a mixture of carbon disulfide (0.1mol, 6.06ml) and diiodomethane (0.1 mol, 8.056ml) in ethanol (15 cm 3 ).The mixture was stirred for about 1h, keeping the temperature at 0 °C.The white solid product so obtained was filtered of, washed with ethanol and dried in vacuum (Desai et al., 2006).

Preparation of the ligand [N-(N-benzilidine aminoethyl)iodomethylane) dithiocarbamate].
Schiff base ligand was prepared as follows: (0.01 mol, 2.74g) of 2aminoethyldithiocarbameto iodomethane dissolved in ethanol 20 cm 3 was mixed with (0.01 mol, 2.10g) of Benzil.The resulting mixture was refluxed with boiling for 2h under constant stirring.The precipitate was then removed from the reaction mixture by filteration, washed with ethanol and dried in vacuum.(Prakash et al., 2011).

RESULTS AND DISCUSSION
The analytical data for the ligand and complexes together with some physical properties are summarized in Table (1).The data from complexes correspond well with the general formula [ML 2 Cl 2 ], where M = Mn(II), Ni(II), Co(II), Cu(II), Zn(II), and Hg(II), L = (C 18 H 17 S 2 N 2 OI).The magnetic susceptibility of the complexes at room temperature was consistent with octahedral geometry around the central metal ion.All the complexes are solid and stable at 25 °C.The complexes are insoluble in common organic solvents but they are relatively soluble in DMF and DMSO.The molar conductance values indicate the nonelectrolyte nature of the complexes in DMF (Geary, 1971), Table (1).

IR Spectra:
The infrared spectra of the ligand are recorded in the 400-4000 cm -1 region and compared with the spectra of the complexes.The characteristic of the ligand and complexes bands are listed in Table (2).The ligand spectrum showed absorption bands at 1679,1618, 1027 and 869 cm -1 that are assigned to υ(C=O), υ(C=N), (C=S) and (C-S), respectively (Nakamoto, 1970).
The band corresponding to υ (C=N) vibration group is shifted to lower values in the spectra of the complexes indicating that the nitrogen atom shared in coordination with metal ion in these complexes (Shaker et al., 2010).The υ (C=O) absorption is also shifted to a lower frequency indicating that the ligand is coordinated with the metal ion through the oxygen of the carbonyl group (Chandra and Gupta, 2005).The υ (C= S), υ (C-S) vibration groups are not shifted to lower frequencies in the complexes indicating that there is no coordination to the metal ions.The other band in the ligand spectrum at 3415 cm -1 is due to the NH group remained unaltered in the complexes indicating that there is no coordination through the NH group.The other band at (542)cm -1 due to (C-I) group remained unaltered in the complexes indicating that there is no coordination through the (C-I) group (Nakamoto,1970).Moreover, all complexes show new bands at (460-511) and (415-425) cm -1 assigned to (M-O) and (M-N) stretching vibrations respectively indicating that the ligand is coordinated through the azomethine nitrogen and carbonyl oxygen (Shaker, 2010).

Electronic spectra:
The electronic spectra of the ligand showed an absorption bands in (29576 -32467 cm -1 ) Table (3), which can be assigned to π π* of the aromatic rings and to n π* transition in the C=O, C=N and C=S chromophoric groups respectively.These transitions were found in the spectra of the complexes but shifted to lower frequencies indicating coordination of the ligand to the metal ion.(Mukta and Singh, 2006).
The electronic spectra of Mn(II) complex had only ligand bands in addition to many very weak absorptions characteristic of d 5 electronic configuration for octahedral high spin complex, d-d transitions due to spin and laporte-forbidden.The very weak bands arise from promotion of an electron to give various excited states containing only three unpaired electrons which may be assigned to the transitions : 6 A 1 g 4 T 1 (G), 6 A 1 g 4 Eg(G ), 6 A 1 g 4 A 1 g (G) , 6 A 1 g 4 Eg(D), and 6 A 1 g 4 T 1 g (p) , exhibit a very small intensity and are conceald by the intraligand transitions.The absorption band at (25371, 30675) cm -1 can be attributed to the charge transfer of ligand to metal.(Chandra and Gupta, 2005).
Cobalt (II) complex gave two bands at 11211, 20921 and 26455cm -1 which were attributed to transitions 4 T 1 g(F) 4 A 2 g (F) υ 2 , 4 T 2 g(F) 4 T 1 g(P) υ 3 respectively and other bands at (29070) cm -1 region which could be attributed to charge transfer transition.These bands are consistent with the octahedral geometry of the complex (Agarwal et al., 2006;Cotton et al.,1999).
Cu(II) complex also showed the presence of one broad band at (14577) cm -1 , which can be attributed to the transitions 2 B 2 g 2 A 2 g, 2 B 1 g 2 B 2 g and 2 B 1 g 2 Eg characteristic for Cu(II) ions in an octahedral environment.(Mahapatra et al., 2010;Monika et al., 2011) Two transitions of the ligand are found also in the spectra of the Zn(II) and Hg(II) complexes, but they shifted towards lower frequencies, confirming the coordination of the ligand to the Zn(II) and Hg(II) ions.(Dunn, 1960 ;Alexia et al., 2007).

Magnetic properties:
The magnetic moment for Mn (II) complex at 25°C temperature was 6.01 B.M, corresponding to five unpaired electrons, the characterization based and metal analyses, suggesting an octahedral geometry (Kulkarni et al., 2009).
For Co(II) complex the magnetic moment was 4.70 BM, this high value is due to the orbital contribution in high spin octahedral geometry (Ajaykumar et al ., 2009).
The Zn(II), and Hg(II) complexes were diamagnetic as expected for d 10 system.Based on these data, an octahedral geometry has been assigned to the Zn(II) and Hg(II) complexes (Dunn, 1960 ;Alexia et al., 2007) (Fig. 1).According to the different results, the ligand behaves as bidentate and coordinate with the metal ions through nitrogen atom of azomethine and oxygen of carbonyl with two chloride ions form octahedral complexes as shown in (Fig. 1).