Formation of Mixed-Ligand Metal Salts in an Organic Phase During Cation-Exchange Extraction with Tetraphenylboronic Acid Salts

Abstract

Significant extraction degree of calcium and yttrium chlorides with solutions of the corresponding tetraphenylborates in tributyl phosphate has been revealed, due to the formation of mixed complex compounds in the organic phase. It has been shown that lithium, calcium, and yttrium tetraphenylborates are significantly dissociated in the organic phase. The process has been studied by conductometry. Based on the obtained data, it has been suggested that the formation of mixed halide complexes is owing to the high energy of the solvated ion pairs [CaL_n]²⁺(A⁻)₂ and [YL_m]³⁺(A⁻)₃ in organic solutions, which is significantly decreased upon the exchange of large tetraphenylborate anions with small chloride anions, possibly with the formation of solvated ion pairs with a lower charge of the cationic part of the complex [CaL_n−1Cl]⁺A⁻ or [YL_m−2Cl₂]⁺A⁻