Synthesis of novel metal complexes of 5-(4-isopropoxyphenyl)-N- phenyl-1,3,4-thiadiazol-2-amine

New5-(4-isopropoxyphenyl)-N-phenyl-1,3,4-thiadiazol-2-amine have been synthesized in good yield by the reaction of N-phenylhydrazinecarbothioamide with a 4-isopropoxybenzoic acid in phosphorusoxychloride. Cr(III), Co(II), Ni(II),Cu(II),Zn(II) and Cd(II) complexes of 5-(4-isopropoxyphenyl)-N-phenyl-1,3,4-thiadiazol-2-amine have been prepared, and characterized by elemental analysis, FT-IR, and UV/visible spectra moreover determination of molar ratio M:L , determination of metal content M% by flame atomic absorption spectroscopy, molar conductance in DMF. solution and magnetic moments ( μ eff.).


Introduction
Thiadiazole contains the fivemembered diunsaturated ring structure composed of two nitrogen atoms and one sulfur atom. There are four isomeric types: 1,2,3-thiadiazole (I); 1,3,4-thiadiazole (II); 1,2,4-thiadiazole (III) and 1,2,5-thiadiazole (IV) 1 been synthesized and  reported to be biologically versatile  compounds having bactericidal, fungicidal, muscle relaxant properties …etc. Some 1,3,4-thiadiazole derivatives possess central nervous system (CNS) depressant activity 2-8 . 2,5-Dimercapto-1,3,4-thiadiazole has been used for many years in flameretardant products 9 . It is utilized in a variety of other applications including synthesizing polymers, in cross linking halogenated polymers; as an additive in lubricating oils and greases; in electrode compositions; as an intermediate or starting material for pharmaceuticals and dyes; as a chelating agent in the analysis of metals; in purifying and treating waste; and as a biocide. It was reported that 1,3,4-thiadiazoles exhibit various biological activities possibly due to the presence of the =N-C-S moiety 10 . In particular, the 1,3,4-thiadiazole derivatives showed these activities [11][12][13][14][15] . Furthermore, a great number of variously substituted 1,3,4-thiadiazoles have been synthesized and tested for their difference activities 16,17 . Substituted thiadiazoles have been reported to display diverse applications as oxidation inhibitor, cyanic dyes and metal complexing agents [18][19][20][21][22] . Metal complexes of 1,3,4-thiadiazole moiety applications. The wide range of application of the ligand and its metal complexes aroused our interest to prepare a new series of some of those metal complexes.

Experimental
All chemical used were of reagent grade (supplied by Either Merck or Fluka) and used as supplied. The FTIR spectra in the range (4000 -200) cm -1 were recorded as cesium iodide disc on FTIR 8300 Shimadzu

Synthesis of Complexes
Addition of ethanol solution of the hydrated metal chloride Cr(III), Co(II), Ni(II) and Cu(II) to an ethanolic solution of (L) in 2:1 (ligand : metal) molar ratios. After stirring for 2hr., colored precipitates formed at room temperature, the rustling solids were filtered off, washed with distilled water dried and recrystallized from ethanol and dried at 90 o C. Preparation of Zn(II) and Cd(II) complexes were prepared in a similar procedure except the molar ratio 1:1 which afforded white and yellow colored complexes in 60 & 70% yield. 892 PDF created with pdfFactory Pro trial version www.pdffactory.com

I. UV/visible spectra
Most of the transition metal complexes are colored 23 and their colors are different from the transition metal salts and the ligand, then this is an important indication to the occurrence of coordination [24][25] . Therefore the colored complexes show different characteristic absorption bands in their position, intensity or both when compared with the bands of the ligand and this was another indication for occurrence of coordination [26][27] .
The peak observed in the electronic spectra are reported in table (2). The origin of band observed at about 700nm in the electronic spectra of complexes has been identified in d-d transition. In these complexes the bands observed at 300-400nm could be assigned to nitrogen-metal charge transfer absorption. Table (2) shows the decomposition point, color and electronic absorption peaks for ligand and complexes. The peaks are classified in to two distinct groups: those that belong to ligand transitions appeared in the UV region while d-d transitions appeared in the visible region. These transitions are assigned in relevance to the structures of complexes and also shown in table (2). II. I-R spectra In the solid state I-R spectra of free ligand showed peak in 3377.1cm -1 due to υNH. The frequencies of the υ(N-H) asm. and υ(N-H) sym. in the complex have suffered from a shift to higher values due to the formation of metal-nitrogen bond, (figures 1,2).
In the free ligand, the band at 1629cm -1 is assigned to the stretching of C = N group showed splitted into two bands related to the two isomethane groups in the thiadiazole ring. One of these bands is shifted to a lower frequency region which indicates the coordination through the nitrogen in position 3 of thiadiazole ring which is probably due to the lowering of bond order of the carbonnitrogen bond resulted from complexation. The second C=N band in the ring is shifted to a higher frequency region due to the changing in the electronic environments of the bond. Stretching of metal-nitrogen bonds of the complexes appeared in low frequency region 497-472 cm -1 . The molar ratio method was followed to detect the ratio of metal ion to ligand in complexes. Ethanol was used as solvent. The

III. Electronic spectral
The U.V.-Visible of the ligand (L) and its metal complexes recorded in table (4). The solution of the ligand (L) in 10 -3 M ethanol exhibited two peaks at 213 & 306 nm, which are attributed to or . The red shift in solution of complexes were investigated depending upon or for all the complexes. The chromium complex showed mixed electronic transition due to low intensity of , the 480nm which is referred to . The square planar geometry of Cu(II) complex in the solid state disappeared due to filling the empty orbital of d -Cu +2 by D.M.F molecule therefore give the peaks at 680nm due to . However Ni(II) complex showed charge transfer at 385nm due to . The complexes of Zn(II) or Cd(II) showed only charge transfer of in the range 307-305nm respectively. 893 poxyphenyl)-N-phenyl-1,3,4-thiadiazol-2-amine

IV. Magnetic Measurements
The magnetic measurements were used to study and identify some paramagnetic transition metal complexes like (Co 2+ , Ni 2+ , and Cu 2+ ) and give us some information about: 1: Oxidation state for transition metal ions to determine the unpaired electrons in metal ion illustrated the complexes state as low spin or high spin. 2: Geometry 3: Bond type The magnetic susceptibility for synthesized complexes at room temperature were measured then the (effective magnetic moment) correlation were measured from this relationship: µeff = 2.828 √ XA. T T = Absolute temperature XA = Atomic susceptibility corrected from diamagnetic The cause of the experimental µe ff values which are lower than the theoretical values attributed to (magnetically dilute) while the cause of the experimental µe ff values which are higher than theoretical values attributed to (orbital contribution) in some cases.
The observed magnetic moment value for the Co(III) complex is 3.60 B.M. which is within the predicted high-spin value for an Tetrahedral Co(III) complex with a considerable orbital contribution to the overall magnetic moment. 27 On the basis of spectral bands, an octahedral geometry is therefore proposed for the Ni(II) ion. The values of ligand field parameters reflect that the M-L bond is quite strong, which in turn suggests sufficient overlapping of the metal orbitals with those of the ligand orbitals.
The compounds are paramagnetic with a room temperature magnetic moment of 4.25B.M. which is consistent with an S = 1 ground state in an Square planner field. V. Molar conductivity measurements: The conductivity measurements have been used in coordination chemistry to identify the ionic compound formula in solution or solid state 28 . From (table 4), it is show that all the complexes are non conducting in solution. VI. According to the results obtained by: C.H.N.M. elemental analysis, electronic spectra and I.R spectra, we proposed the following stereo chemistry of the complexes.