Spectrophotometric study of kinetics and associated thermodynamics for the complexation of Pr(III) with L-proline in presence of Zn(II)

Abstract

The complexation of L-proline with Pr(III) has been studied in presence and absence of Zn(II) in different environments by employing 4f–4f absorption transition spectra. The study was carried out through the computation of various spectral parameters namely energy interaction (Slator– Condon (Fk’s), nephelauxetic effect (b), bonding (b1/2) and percent covalency (d) parameters) and intensity parameters (oscillator strength and Judd–Ofelt parameters). Pr(III), being a paramagnetic shows characteristic 4f–4f transition bands (3H4 fi 3P2, 3P1, 3P0 and 1D2) in the visible region. The intensities of these bands became more prominent in presence of Zn(II) suggesting the evolvement of Zn(II) towards the complexation of Pr(III) and L-proline. This intensification of bands is visualized to be due to the increased probability of interaction between 4f-orbital of metal ion and ligand. As well as these bands have been found to be highly sensitive to even minor changes in the immediate coordination around Pr(III), occurring as a result of the progress of heterobimetallic complexation of L-proline with Pr(III) and Zn(II). The sensitivities of these bands in terms of oscillator strength have been utilized to monitor the simultaneous coordination of L-proline with Pr(III) and Zn(II). The rate of complexation with respect to 4f–4f transition bands has been determined. The determined activation and thermodynamic parameters corresponding to rate constant were found to be highly favourable for the heterobimetallic complexation of L-proline with Pr(III) and Zn(II).