Synthesis and Characterization of Some Schiff Bases ( derived from thiazole ) and Their Complexes With Co ( II ) , Ni ( II ) and Cu ( II )

The synthesis of some new coordination compounds for cobalt (II), nickel(II)and copper(II)with Schiff bases derived from(2-aminobenzothiazole,6-nitro-2aminobenzothiazole,4,6-dibromo-2-aminobenzothiazole) and 4-N-dimethylbezaldehyde to give ligands (La,Lan and Ladb) were prepared and then reacted with metal salts in ethanol as a solvent in 1:2 ratio (metal : ligand). The complexes which have the general formula [ML2Cl2] Where M=Co (II) , Ni (II) and Cu (II),( L=La,Lan,or Ladb) all ligands and it's metal complexes were characterized using metal analysis by Atomic absorption, Infrared spectra ,Electronic spectra, Molar conductance and Magnetic moment measurements ; These measurements indicated that the ligands coordinate with metal (II) ion in a bidentate manner through the nitrogen atoms in ligands, Octahedral structures were suggested for metal complexes. Introduction Schiff bases derived from an amine and aldehyde are an important class of ligands that coordinate to metal ions via azomethine nitrogen and have been studied extensively(Arora & Sharma,2003;Vigato & Tamburini,2004 and Katsuki,1995). These complexes are play an important role in the development of coordination chemistry( Sousa et al.,2003;Kou et al.,2004). Thiazole derivatives have been found a number uses in medicinal and pharmaceutical fields(Malik & Rajeev,1982). Some of them have been showed to have antitumer activity(Bradshaw ,2002;Ioaizaperez,2002 and Racane,2006)anticandidous(Sidoova et.al,1997)Parkinson ' s disease (Alain et.al,1997) antihistaminic and antiflammatory (Abignente et.al,1983).Benzothiazole have also shown significant effect against cancer (Swarnkar et.al, 2007)and antibacterial agent (Lednicar & Matcher,1997; Karia & Parsania,1999) .Another area of application of these Schiff bases is analytical chemistry where some of compounds were used as ligand in complexometry topic (Rodriguez et.al,2004) and catalysts as a corrosion


Introduction
Schiff bases derived from an amine and aldehyde are an important class of ligands that coordinate to metal ions via azomethine nitrogen and have been studied extensively (Arora & Sharma,2003;Vigato &Tamburini,2004 andKatsuki,1995).These complexes are play an important role in the development of coordination chemistry ( Sousa et al.,2003;Kou et al.,2004).
Thiazole derivatives have been found a number uses in medicinal and pharmaceutical fields (Malik & Rajeev,1982).Some of them have been showed to have antitumer activity (Bradshaw ,2002;Ioaizaperez,2002 andRacane,2006)anticandidous (Sidoova et.al,1997)Parkinson ' s disease (Alain et.al,1997) antihistaminic and antiflammatory (Abignente et.al,1983).Benzothiazole have also shown significant effect against cancer (Swarnkar et.al, 2007)and antibacterial agent (Lednicar & Matcher,1997;Karia & Parsania,1999) .Another area of application of these Schiff bases is analytical chemistry where some of compounds were used as ligand in complexometry topic (Rodriguez et.al,2004) and catalysts as a corrosion inhibitor in chemical industry (Ramesh & Sivagamasundari,2003) .Thus the aim of this work to prepared some new transition metal complexes of Schiff bases derived from substituted benzothiazoles prepare and characterized of these complexes.

Materials:
All the chemicals were supplied by BDH and Fluka and used without further purification.

Instruments:
The following Instruments have been used for spectroscopic measurements and physical properties for ligands and their complexes :-1-Infrared spectra were record by a SHIMADZU infrared spectrophotometer FT-IR model 8400S in the 4000-400cm -1 Range using KBr disc.2-Electronic spectra were recorded on HITACHI model 2000U spectrophotometer using DMSO as a solvent.3-Melting point or decomposition temper.were determined by an Electro thermal melting point model 9300.4-Magnetic susceptibility measurement were measured on by Faraday method at 25C o using Bruker BM 6 instrument .5-The molar conductivity of complexes (0.001M) in DMSO was measured using HANNA model 214EC conductivity meter.6-Determination of metals percentage by atomic absorption spectrophotometer on Perkin-Elmer model 2280.

• Preparation of the complexes :
The complexes were prepared by dissolving (2mmole) of (La) or (Lan) or(Ladb) in 40 ml absolute ethanol which then added drop wise with stirring to (1mmole) of MCl 2 metal salts M=Co(II), Ni(II) and Cu(II) which were dissolved in 10 ml of hot distilled water.The mixture was heated to 50C ° for 30 min., then left overnight.The precipitated complex was filtered off, washed with 10 ml cold ethanol and dried.

Results and Discussion
Characterization of ligands and it's metal complexes: The ligands and it's metal complexes were insoluble in water but soluble in organic solvents such as DMSO,DMF and Ethanol ,low conductivity values(8.15-13.20 cm 2 ohm -1 mol -1 )indicated that the complexes are nonelectrolytes (Shallary et.al, 1979;Geary,1971).The metal percentage in complexes analytical and some of physical data of ligands and complexes are given in Table (1).

Infrared spectra:
The important infrared spectra data of ligands and their complexes are given in Table (2),The bands in the region 1625-1633 cm -1 and 1600-1615 cm -1 due to ν(C═ N) vibration of thiazole ring and azomethine group in the ligands respectively.These values are increased(thiazole ring) and shifted to lower frequencies(azomethine group) after copmlexation ( EL-Bindary & EL-Sonbati, 1999).The bands ν(C-S-C) in region 750-755 cm -1 which remains in the same region in free ligands and after copmlexation that mean's the sulfur atom in thiazole group doesn't coordinate with metal in complexes (Chattopadhyay & Sinha, 1996).New weak bands in the region 415-450 cm -1 were observed in the spectra of metal complexes , which were not appeared in the spectra of ligands due to ν(M -N) (Nakamoto,1986;Arpalahti & Lehikoinen, 1990) .• The Electronic spectra and magnetic measurements

Table (2): IR absorption bands of ligands and their complexes in cm
The electronic spectra of ligands (La ,Lan and Ladb) show strong bands in the range 41150-42210cm -1 and 33210-33420cm -1 which are attributed to     and    n respectively.The electronic spectra of Cobalt (II) complexes showed two absorption bands at 15250-15730cm -1 and 23230 -23470cm -1 these were assigned to 4 T 1 g (F) → 4 A 2 g (F) (ν 2 ) and 4 T 1 g (F) → 4 T 1 g (P) (ν 3 ) transitions respectively, which are characteristic of octahedral stereochemistry.The magnetic moment of cobalt (II) has been found to be (4.79-5.21 B.M) this values of magnetic moment is higher than the spinonly value (3.87 B.M) for there unpaired electrons and may be ascribe to substantial orbital contribution to the moment which is applicable of high spin octahedral Cobalt (II) complexes(Nicholas1973) (Figgis& Lewis,1960).The magnetic moment for nickel (II) complexes are (2.43-3.60B.M) and the spectra of this complexes show bands at 15225 -15435 cm -1 and 21110 -21290 cm -1 which may have existence of 3 A 2 g (F) → 3 T 1 g (F) (ν 2 ) and 3 A 2 g (F) → 3 T 1 g (P) (ν 3 ) transitions therefore an octahedral configuration suggested .The magnetic moment values of copper (II) complexes (1.86-1.91B.M) which may expressed an octahedral structure.Electronic spectra of these complexes a band show one broad band at 14895-15320 cm -1 due to two or three transitions 2 B 1 g → 2 A 1 g , 2 B 1 g → 2 B 2 g and 2 E 2 g → 2 T 2 g suggesting a distorted octahedral structure (Nicholas,1973;Figgis & Lewis,1960).The spectral data and magnetic moments of prepared complexes were given in Table (3).

Table(3): Electronic spectra and magnetic moments of the complexes.
According to these results the octahedral structure suggested for Co(II), Ni (II) and distorted octahedral due to Jahn-Teler effect Cu(II) complexes The Schiff bases coordinate with metal(II) ions through the nitrogen of the azomethine group and nitrogen of thiazole ring (Fig. 2).