X-RAY K-ABSORPTION NEAR-EDGE STRUCTURE STUDIES OF SOME MIXED-LIGAND COBALT (II) COMPLEXES

X-ray absorption near edge structure (XANES) measurements have been made on the K-edges of cobalt in the five oximinoacetone thiosemicarbazone (oatsc) complexes of cobalt viz., [(Co(oatsc)2 (oAc)2]; [Co(oatsc)2 (Br) 2]; [Co(oatsc)2(Cl)2]; [Co(oatsc)2(ClO4)2] and [Co(oatsc)2(NO3)2]. These complexes are important from the pharmacological point of view. The present XANES studies reveal that as far as the structure is concerned, the four complexes with (oAc)2, Br2, Cl2 and (ClO4)2 ligands are similar and these ligands are part of the first coordination sphere. In [Co(oatsc)2(NO3)2] we find that one nitrate group is inside the coordination sphere, whereas one nitrate group is outside the coordination sphere. Our studies establish the relative ionic character in the order [Co(oatsc)2(NO3)2] > [Co(oatsc)2(ClO4)2] > [Co(oatsc)2(Cl)2] >[Co(oatsc)2(Br)2] > [Co(oatsc)2(oAc)2 The average metal-ligand bond distance have been estimated and explained on the basis of the structures of the complexes.