Isoequilibrium and free energy relationships in complex formation equilibria between Ag(I) and thiocarbonyl ligands in oxygenated solvent media

Abstract

The standard enthalpy and entropy changes for the stepwise and overall complex formation homogeneous equilibria between Ag(I) and thiocarbonyl ligands or for the single reactions (series of reactions) in H₂O, CH₃OH (MeOH), C₂H₅OH (EtOH), C₃H₇OH (n-PrOH), CH₃CHOHCH₃ (Is-PrOH), and CH₃COCH₃ (Ac) are linearly correlated (corr. coeff. R > 0.9). The intercepts of the ∆H − ∆S regression straight lines ∆H = ∆H_res− τ ∆S depend on both solvent and number of coordinated ligands (hereafter coordination level) in the coordination sphere of the substrate AgL_n. The slopes τ = d∆H/d∆S (hereafter susceptivities/sensitivities) depend only on solvent. Robust and sound hard solvent parameter scales, founded on solute–solute soft–soft interactions, can be set up on ∆H_res and/or τ bases. At 25 °C, the transfer standard free energies for the overall complex formation reactions at the single coordination levels n = 1, 2, or 3 between the various solvents are uncorrelated. When considered as unique set with n = 1, 2, and 3, the results linearly correlated (0.85 ≤ R ≤ 0.97) with slope ≈ 1 and intercepts depending on the actual couple of solvent media. The enthalpy(entropy) changes are uncorrelated.

Keywords:

• Enthalpy–entropy relationships
• isoequilibrium
• Ag(I) thiocarbonyl complexes
• non-aqueous solvents