Studies of cyanide–xanthate mixed ligand complexes of mercury(II) in aqueous solution

Abstract

Mercury(II) has been shown to form soluble mixed-ligand complexes with cyanide and alkyl xanthate (ROCS₂^–) ions. At total mercury(II) concentrations <0·006M and at total cyanide to total xanthate ratios between 2·1 : 1 and 4·5 : 1, the complex is of the form Hg(CN)₂X^–(X = ROCS₂^–), and absorbs at 255 nm. On the basis of free xanthate concentrations determined spectrophotometrically, stability constants β₁₂₁=[Hg(CN)₂X^–]/[Hg²⁺]-[CN^–]²[X] were calculated. The values obtained were (1·5 ± 0·1)× 10³⁵, (1·8 ± 0·1)× 10³⁵, (2·7 ± 0·2)× 10³⁵, and (3·5 ± 0·6)× 10³⁵, respectively, for methyl, ethyl, butyl, and hexyl xanthate, at 25 ± 0·5 °C. The overall enthalpy and entropy of formation of the ethyl homologue are –50·5 kcal. mole^–1 and approximately –8 cal. mole^–1 deg.^–1, respectively. At mercury(II) concentrations greater than 0·006M, the concentration of a second mixed ligand species becomes significant. This species absorbs at between 302 and 303 nm, and cannot be studied by the experimental methods used in this work.