Absorption spectroscopy has been used as tool to understand the coordination of mixed ligand complexes of praseodymium (III) [PrCl3(H2O)7], with hexafluoroacetylacetone[C5H2O2F6] and their complexes with pyridine [C5H6N],chloropyridine [C5H6NCl]&bromopyridine [C5H6NBr].Using comparative absorption spectroscopy involving 4ƒ-4ƒ transitions in various solvents, like methanol (CH3OH), acetonitrile (CH3CN) and dimethylformamide [(CH3)2NCOH].The change in coordination sphere in various solvent medium is observed. The 4ƒ-4ƒ transition spectra yield sharp bands which were analyzed individually by Gaussian curve analysis, the energy interaction parameters (FK,EK), Lande spin orbit coupling (ξ4f), nephelauxetic ratio (β), bonding parameter (b1/2), percent covalency (δ), oscillator strength were calculated and the Judd-Oflet intensity parameters of 4f-4f transition have been computed on computer using partial multiple regression analysis. The intensity of hypersensitive transitions has been used to distinguish between outer and inner sphere coordination, in identifying the coordinating sites of ligands. These parameters oscillator strengths electronic dipole parameter gives information about nature of binding between lanthanide metal and ligands complexes in different solvents.
