STUDIES ON SOME LANTHANIDE COMPLEXES OF HIGHER COORDINATION-NUMBER - SYNTHESIS AND CHARACTERIZATION

Lanthanum(III), cerium(III), praseodymium(III), neodymium(III), samari um(III) and europium(III) form complexes in 1:1, 1:2 and 1:3 stoichiom etric ratios with the ligands 2-thiophenealdehyde salicyloylhydrazone (tash) and indole-3-aldehyde semicarbazone(iasc). The complexes have b een characterised on the basis of elemental analyses, spectral, magnet ic and thermal data. tash is a tetradentate ligand forming complexes u pto maximum coordination number of twelve for the lanthanide ion where as the iasc behaves as bidentate and the other coordination sites are occupied by aqua/or acido ions. The spectral parameters bonding (b(1/2 )), covalency angular overlap(eta), Sinha's covalency (delta), have be en calculated and indicate partial covalent bonding developing between the lanthanide metal and ligand in these complexes. Higher (mu)RT val ues for Sm(III) and Eu(III) complexes along with structural characteri stics of the lanthanide complexes are discussed.