THIOAMIDE ADDUCTS OF ZINC-GROUP CHLORIDES - A THERMOCHEMICAL STUDY

The standard molar enthalpies ΔrH°m of the adducts of zinc-group chlorides with thioacetamide (ta) and thiobenzamide (tb) have been determined through reaction-solution calorimetry at the temperature 298.15 K: MCl2(cr) + vL(cr) = MCl2 · vL(cr); ΔrH°m/(kJ · mol-1): ZnCl2 · 2ta, -(62.09±0.33); CdCl2 · 2ta, -(45.77±0.30); HgCl2 · ta, -(61.59±0.28); ZnCl2 · 2tb, -(52.26±0.69); CdCl2 · tb, -(19.44±0.20); and HgCl2 · 2tb, -(76.81±0.09). From ΔrH°m the standard molar enthalpies of formation of the crystalline thioamide adducts were calculated; the values decrease from zinc to mercury within the ta: { -(623.2±0.9) to -(358.9±1.1)} kJ · mol-1 and tb: {-(377.0±3.1) to -(210.7±3.2)} kJ · mol-1, series. The mean metal-sulphur bond dissociation enthalpies decrease with increase of number of ligands, and are roughly of the same size as the equivalent metal-oxygen bond for zinc and cadmium. The softer behaviour of mercury favours its bonding to the sulphur donor atom. © 1992 Academic Press Limited All rights reserved.