Spectroscopic study of rare earth chlorocomplexes in propylene carbonate

Abstract

Absorption spectra of Et 4N +(ClO 4 −, Cl −) 0.18 M lanthanides in propylene carbonate (PC) solutions were investigated in the near UV, visible and near IR. The multiwavelength numerical treatment is based upon the optical density matrix rank analysis and an original optimization calculation, which leads to simultaneous determination of the overall stability constants and specific extinction coefficients of the complexes. The constitution of the rare earth chloride PC solutions, after testing several theoretical models, is limited to LnCl 2+ and LnCl 2+, the latter being the more substituted Ln(III)-chlorocomplex, as shown by the identical absorption bands assigned in the solid state and calculated in solution: the overall stability constants are 54, 92, 80 for LnCl 2+, 1.6 × 10 3, 5.2 × 10 3, 1.0 × 10 4 for LnCl 2 + where Ln is Pr, Nd, Sm respectively. Stabilization of the complexes with respect to the lower donor strength of propylene carbonate compared with methanol is found; however, the values of the calculated stability constants are consistent with the formation of weak complexes. The solvent effect upon the electronic spectra is also illustrated by better separated absorption bands in PC than in anhydrous methanol.