Revision and Analysis of the Formation Constants of Rare Earth Diketonates

Abstract

Over the course of the past several decades, spectroscopic surveys have unveiled the intricate nature of the aqueous chelation of Rare Earth Metals. Herein, we have collected a large data set about the interaction between 16 metal ions (Sc³⁺, Y³⁺, La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, and Lu³⁺) and perfluorinated nonsymmetric β-diketones, which contain chalcogen-bearing heterocyclic rings or aromatic moiety. The role and influence of the side ions on the chelation processes have been re-estimated to obtain revised stability constants. After analysis of more than 150 revised formation constants, a better periodic correlation has been shown. Scrutinizing the effects of the substituted group has revealed an “anti-Coulomb” behavior within the chalcogen group of diketones and a strictly electrostatic trend within the Rare Earth Metals series. Within the first-order approximation, the spin–orbit contribution to the Gibbs free energy of chelation has been estimated.