Solubility of cadmium cyanide and the formation constants of the cadmium-cyanide system in dimethylformamide at 25°C

Abstract

A solubility column technique has been used to measure the solubility of cadmium cyanide in dry dimethylformamide over a range of ionic strengths. The results showed that cadmium cyanide did not behave as a completely dissociated 2:1 electrolyte in this solvent. Evidence for the existence of the species CdCN⁺, Cd(CN)₂, Cd(CN)^–₃ in these solutions has been obtained from experiments on solutions containing either excess cyanide or excess cadmium salt. The first three successive formation constants (K₁, K₂, K₃), and the solubility constant (K_s2), valid at 25°C in a medium containing tetraethylammonium perchlorate at a total ionic strength of 0.1 have been calculated as: log K₁= 4.7; log K₂= 4.4; log K₃= 3.08; log K_s2=–2.60. The tetracyanocadmate ions was not detected, and the anionic complexes appear to be less stable in relation to the stabilities of the lower complexes than is the case in either 3M aqueous NaClO₄, or 0.25 M NaNO₃ in ethylenediamine. Difficulties over the true significance of K₁, K₂ are pointed out.