Coordinating Properties of Aromatic and Aliphatic Sulfur with Bivalent Metals in Aqueous Solution. A Calorimetric Study

Abstract

Heats and entropies of complex formation of the thiophen-2-carboxylate ion with Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ have been determined by direct calorimetry, the formation constants being known from the literature. The measurements were carried out in aqueous medium at 25ºC and an ionic strength of 1. The values of the thermodynamic quantities for thiophen-2-carboxylate, compared with those for (ethylthio)acetate and (phenylthio)acetate obtained previously, indicate a greater tendency for aromatic sulfur to form bonds with the above metals than for aliphatic sulfur. The causes of this behaviour are discussed.