Synthesis and Theoretical Evaluation of New Binuclear Cr(III), Co(II) and Fe(III) Metal Complexes of Tetradentate Schiff Base and Its Biological Activity

diyl)bis(azan-1-yl-1-ylidene))bis(ethan-1-yl-1-ylidene) bis(4-hydroxy-6-methyl-2H-pyran-2-one) derived from condensation of one mole diethylene diamine triamine (dien) with two moles of dehydroacetic acid have behaved tetra dentate dibasic chelating agent with all metal ions under study. Three bimetallic Cr(III), Co(II) and Fe(III) acyclic polydentate complexes [M 2L2Cl 2]Cl 4 ,M=Cr(III) , Fe(III) and [M 2L2Cl 2], M=Co(II) have been prepared and fully characterized by UV-Vis., FTIR, micro-elemental analysis , as well as the magnetic moments of solid complexes and the measurements of molar conductance in DMSO s olution helped us in investigate the chemical structure of bimetallic models . From the results obtained by different techniques, it was found that the proposed structures of the prepared complexes have octahedral structure. A theoretical treatment of the formation of complexes in the gas phase was studied, this was done


INTRODUCTION
The binuclear metal complexes possessing heterocyclic rings are one of the most widely used as antibiotics, antifungal and semiconductor sensors [1][2][3][4]. Now days, there exists interest in the development of new and more effective antifungal compounds [5], urged infection by the increasing importance of opportunistic provoked by factors that depress or destroy the immune system, like chemotherapy of cancer, the use of drugs to avoid organ rejection in transplanted patients and discussed like AIDS [6]. According to that, the development of new systemic fungicides is of prime importance in modern medicinal chemistry. 3-acetyl-6-methyl -2Hpyran-2,4(3H)-dione [I]a commercially available compound usually obtained through the on to condensation of ethyl acetate [7] has been shown to posses modest antifungal properties [8]. Also, it has been shown that the complexes of dehydroacetic acid with zinc and several transition metal cat ions, are fungi static [9]. This has motivated our study on the synthesis and structural characterization of new bimetallic complexes of Cr(III), Co(II) and Fe(III) with new acyclic Schiff base [L] derived from condensation of diethylenetriamine with dehydroacetic acid.

Physical Measurements
Electronic spectra of the new ligand and its metal complexes were recorded in the region 800-200nm on Shimadzu 670 spectrophotometer. IRspectra were recorded on PC. Shim adz FT-IR spectrophtometric -Japan model as KBr and CsIdisic in the range 400-4000cm -1 . Magnetic moments studies were carried out on magnet-Bruker balance MG. On Al-Nahrain university Laboratories. The conductivity of solution of 10 -3 Mcomplexes in DMSO were done on digital conductivity meter (HPG system, G-3001).
As well as the micro analysis, of C.H.N, were recorded at Carolo Erba 1108 elemental Vario in Laboratories of chemistry Depart in Al-Mustanisrya University. As well as %M in solid complexes were estimated using standard methods [10].

Reagents and Solvents
Dehydroacetic acid and diethylenetriamine (dien) obtained from Merk, was used as supplied, and the metal chloride hydrated CrCl 3 .6H 2 O, CoCl 2 .6H 2 O and FeCl 3 . 6(H 2 O) of An. grade, were used for synthesis of complexes without any purification.

Synthesis of Metal Complexes
(0.65 g, 2 mole) of (CrCl 3 . 6H 2 O) in (20mL) methanol was added to (0.5g, 1mol)of [L] ligand dissolved in methanolic solution of potassium hydroxide(5%) to keep the pH of the solution for( ≈8). The resulting mixture was refluxed under nitrogen atmosphere for 3 hrs. until its solution has become green in color, then cooled to room temperature, a green precipitate formed, filtered off, washed several times with 15ml of diethyl ether ,and dried under vacuum to afford(0.51g, 61%) yield, scheme(2), A similar method was used to prepare Co(II), and Fe(III) complexes Scheme (2), Table (1) shows some physical properties and reactant amount of the prepared complexes.

Study of Biological Activity for Ligands and Their Metal Complexes
The biological activity of the ligands and their metal complexes were studied against two selected type of bacteria which included Escherichia coli, as gram negative (-Ve) and Staphylococcus aureus as gram positive (+Ve) to be cultivated and as control for the disc sensitivity test [11]. This method involves the exposure of the zone of inhibition toward the diffusion of microorganism on agar plate. The plates were incubated for 24 hours at 37°C, the zone of inhibition of bacteria growth around the disc was observed.

RESULTS AND DISCUSSION
The new acyclic Schiff base [L] ligand derived from condensation of one mole diethylenetriamine with two moles of dehydroacetic acid have behaved tetra dentate dibasic chelating agent with all metal ions understudy. The stochiometric of the ligand and its complexes were confirmed by their elemental analysis.

Infrared Spectra
The IR spectrum of the (L) ligand shows bands in the region at 3400cm -1 and 1656cm -1 , which assignable to υ(OH) and azomethane group υ (C=N) [12]. As well as the work absorption at 1695cm -1 attributed to the υ(C=O) of the pyrane group. The IR showed no bands around at 3571 and 3357cm -1 assigned to the υ asy (N-H) and υ sy (NH) respectively which indicate the absent of υ asy (N-H) and υ sy (NH) [13]. The negative shift generally in υ(C=N) further suggested the coordination to metal ions through nitrogen atom of (-C=N-) Schiff's base [12] of the ligand.
The observations indicate the coordination of the ligand L through the carbonyl group stretching frequency decreases to 1650-1640cm -1 compared to the free ligand at 1695cm -1 , due to the charge transfer from the ligand to the metal [13]. The band assigned to the phenolic OH group in the same wave number comparing with that of the free ligand, proving it's not involve coordination. [12] ( Table 2). New bands which appeared at low frequencies in the spectra of the prepared complexes were probably due to (metal-nitrogen), and (metal-oxygen), [14] ( Table 2).

Electronic Spectra and Conductivity Measurements
The free ligand (L) in methanol spectral exhibits three distinct absorptions in the range 42735, 37878 and 31847cm -1 which are assigned to ߨ-ߨ* of benzenoid and E1, E2 and n-ߨ* of C=N, and C=O chromospheres [15]. The green solution of Cr (III) complex in DMF exhibits absorption in the range 22250, 25666 and 37017cm -1 , which resemble these reported to be octahedral. Thus, assuming the effective symmetry to be Duh, and the various bands can be assigned to 4 A 2 g(F)→ 4 T 2 g(p), 4 T 1 g(F)→ 4 T 1 g(P) respectively [15]. The Co(II) complex solution exhibit a well weak absorption in visible region at 25545cm -1 , 20955, 19955cm -1 which can be assigned to 4 T 1 g(F)→ 4 T 2 g and 4 T 1 g→ 4 T 1 g(p) respectively [16]. The measurements of molar conductance in DMSO , ࢫm 90 S.cm 2 ml -1 for Co(II) showed that these are electrolytic and 115, 125 S.cm 2 ml -1 for Cr(III) and Fe(III)respectively which showed electrolytic [10].

The Magnetic Measurement
The magnetic moment of Cr(III)(∼ 3.35BM) revealed the present of three unpaired electrons which agree with octahedral environments around Cr(III) ion, as well as the magnetic moment of Co(II), (∼ 1.55BM) [11]. The magnetic moment of Fe(III)(∼ 3.34BM) revealed which agree with octahedral environments around Fe(III) ion [17]

The Proposed Structure
Based on various physiochemical studier like elemental analyses, conductively measurements, magnetic moments, UV-Visible, and IR spectral studies, a distorted octahedral geometry may be proposed for Cr(III),Co(II) and Fe(III) complexes, as shown in scheme (2).

Theoretical Study
The ball and cylinders and some of selected structural parameters (bond length and angles) of the optimized geometries are shown in Fig. 1 Table 4. As shown in this figure, there is no obvious trend for the variation of these parameters. The values of the bond length and angles of the optimized geometries are quite similar to the experimental results of the corresponding compounds.

Biological Activity
The antibacterial activity of the Schiff bases and its complexes were tested on Gram positive bacteria, Staphylococcus aureus and Gram negative, E. coli. The antibacterial activities of the samples were evaluated by measuring the inhibition zone observed around the tested materials as shown in Fig. 2.
The improved activity of metal complexes can be explained on the basis of chelation theory [18]. The cobalt complex showed the highest value of inhibition against all types of micro organisms, this indicates that the chelation tends to make the ligand act as more powerful and potent antimicrobial agents, thus, inhibiting the growth of bacteria and fungi more than the parent ligand. The structural changes have marked effect on the sensitivity and sensitivity varies with organisms.  and structural study of above new type of octahedral complexes have bidentate ligands. The study of biological activity of the ligands and their metal complexes against two selected type of bacteria which included Escherichia coli, as gram negative (-Ve) and Staphylococcus aureus as gram positive (+Ve) to be cultivated and as control for the disc sensitivity test shows that different activity of inhibition on growth of the bacteria.