Scrutiny of Application of the Quadratic Curves to the Lanthanide Tetrad Effects in Two Organic Solvent Extraction Systems

摘要

Based on a large-scale magnification of a diagram presented by Peppard et al. (1969), the logarithms of the concentration ratios of lanthanides in aqueous phase to those in organic phase have been closely estimated for two cases. The differences of the observed values from straight lines connecting directly between La and Gd and between Gd and Lu were scrutinized in connection with the applicability of the quadratic function and with the distortion from it. In case of partitioning between 0.05M HCl and 0.3M di n-octyl phosphinic acid (benzene), two regular cycles of low and high quadratic symmetry were recognized. The features observed are explicable in terms of spatial configuration (degree of steric symmetry) of f electrons themselves, strength of directional preference of ligand-cation bonding and interaction between these two factors. Contrastingly, the system comprising di 2-ethylhexyl chloromethyl phosphonate appears to suggest the state of 4f electron subshell under very weak ligand field.