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Abstract
Stability constants for the cyanide complexes of zinc(II) and cadmium(II) have been determined in five acetonitrile-water mixtures containing up to 70% (v/v) MeCN. The constants were measured at 25°C and an ionic strength of 1M NaClO4 by high precision glass electrode potentiometry. Complexes containing up to four cyanide ions have been detected for both Zn(II) and Cd(II) although the lower order complexes ZnCN+ and Zn(CN)2° are difficult to quantify because of the sparing solubility of the zinc cyanide salt. The stability constants for both systems increase monotonically with MeCN concentration and show a striking similarity. Evidence for the formation of ternary hydroxocyano-metal ion complexes was obtained at high pH values but their stability constants could not be evaluated because of the lack of quantitative information for the binary M(II)-OH− species.