4f-4f absorption spectra of nine-coordinate Pr (III) and Nd (III) complexes in different environments.

Absorption spectroscopic studies on the mixed-ligand complexes of Pr (III) and Nd (III) with 2,2'-bipyridyl and thiocyanate in pyridine, DMSO, DMF and methanol are presented. The oscillator strengths for the hypersensitive and non-hypersensitive transitions have been calculated and variation in the oscillator strength and band shapes with respect to solvent type is rationalized in terms of solvent structures and coordinating properties. A comparison is made with 1,10-phenanthroline complexes and has been shown that bpy is a weaker ligand than phen for these ions. Pyridine has been found most effective in promoting 4f-4f intensity and the increase in the oscillator strength in this solvent is due to dynamic ligand polarization mechanism.