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Cyanide thermodynamics. Part 4.—Enthalpies and entropies of cyanide complexation of CuI, AgI, ZnII and CdII
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Cyanide thermodynamics. Part 4.—Enthalpies and entropies of cyanide complexation of CuI, AgI, ZnII and CdII

S. Jose, P.M. May and G. Hefter
Journal of the Chemical Society - Dalton Transactions, Vol.92, pp.641-644
1996
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Abstract

The enthalpy changes associated with the complexation of CuI, AgI, ZnII and CdII by cyanide to form Cu(CN)43–, Ag(CN)2–, Zn(CN)42– and Cd(CN)42– have been determined by titration calorimetry in (wherever possible) both aqueous NaCl and NaClO4 media at an ionic strength of 1 mol 1–1 and 25 °C. The corresponding entropy changes were calculated by combining these data with stability constants from the literature. The H values show little dependence on the medium but the S values vary considerably. This is attributed to competitive complexation of some of the metal ions by Cl–. The great stability of the cyanide complexes in aqueous solution is shown to be due entirely to the favourable H term as S is negative. Possible reasons for these effects and their variation between metal ions are discussed in terms of the solvation characteristics of the species involved.

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