Thermodynamic relationships of complex formation: Part 5. Isoequilibrium relationships in soft-soft interactions in hard solvents

Abstract

The inspection of the Δ H-Δ S patterns for reactions between Ag(I) complex substrata and various entering ligands discloses linear interplay between the two parameters. The actual Δ H (Δ S) values demonstrate that soft-hard interactions can produce favourable enthalpy changes coupled to unfavourable entropy changes, and confirm that soft-soft interactions can yield unfavourable enthalpy changes coupled to favourable entropy changes. These results, together with the already published enthalpy-entropy interplays, which show negative values of both Δ H and Δ S for hard-hard interactions in aqueous solution, demonstrate that in this solvent soft-soft (hard-hard) interactions do not necessarily produce Δ H < 0 (Δ H > 0) coupled to Δ S < 0 (Δ S > 0) because their values also descend from the role of the solvent molecules in the specific reaction. The coordinated solvent produces a sort of ‘shielding’ or ‘levelling’ of the acceptor and donor abilities.