THERMAL AND SPECTRAL PROPERTIES OF LANTHANIDE(III) COMPLEXES OF 3-AMINO-2-HYDROXY-1,4-NAPHTHOQUINONE

Octa-coordinated La(III), Ce(III), Pr(III), Nd(III), Sm(III), Gd(III) and Dy(III) complexes of 3-amino-2-hydroxy-1,4-naphthoquinone (3A2HNQ) of general formula [M(3A2HNQ)(3)(H2O)(2)] have been synthesized and c haracterized. The non-isothermal thermogravimetric profiles indicate t he loss of one of the coordinated ligands along with one coordinated w ater molecule at a significantly higher energy of activation than that of the second step of decomposition with loss of two ligands and one water molecule. Such a difference in the energy of activation for the two steps can be correlated to the strong intermolecular hydrogen bond ing interactions between quinone carbonyls and coordinated water molec ules. These chelates exhibit slightly lowered magnetic moments probabl y due to their polymeric nature. IR and far-IR spectral data suggest t hat phenolic oxygen and amino nitrogen are the coordinating sites for 3A2HNQ, while coordinated water molecules are involved in the intermol ecular hydrogen bonding interactions with free quinone carbonyls of 3A 2HNQ molecules. The nephelauxetic ratio (beta), covalency factor (b(1/ 2)) and Sinha's parameter (delta) evaluated from electronic spectral s tudies of Ce(III), Sm(III), Gd(III) and Dy(III) reveal a negligible am ount of covalency in metal-ligand bonding.