Thermodynamic and spectroscopic studies on the complexation of silver(I) by mixed phosphorus–nitrogen ligands in dimethyl sulfoxide and propylene carbonate

Abstract

The results of a thermodynamic study concerning Ag(I) complexation in dimethyl sulfoxide (dmso) and propylene carbonate (4-methyl-1,3-dioxolan-2-one, pc) with the mixed P–N ligands: 1-(diphenylphosphino)-2-(dimethylamino)ethane (Me₂Npe), 1-(diphenylphosphino)-2-(dimethylamino)benzene (Me₂Npph), 1-(diphenylphosphino)-3-(dimethylamino)propane (Me₂Npp) and 1-(diphenylphosphino)-2-(2-pyridyl)ethane (ppye) are reported. Potentiometric and calorimetric measurements have been performed to obtain, respectively, free energy and enthalpy data for the reactions at 298 K and 0.1 mol dm^–3 ionic strength (NEt₄ClO₄). A common feature of the different ligands is the formation of successive mononuclear complexes [AgL_j]⁺ (j = 1–3) both in dmso and pc. In the former solvent Me₂Npph gives only the first two species. Me₂Npe, Me₂Npp and ppye also form appreciable amounts of the dinuclear species [Ag₂L]²⁺ and [Ag₂L₂]²⁺ in pc. All the complexes are strongly enthalpy stabilized, the entropy changes being unfavourable. The ligands behave as P donors in dmso, while are normally chelating or bridging in behaviour in pc, depending on the stoichiometry of the species formed. The results are discussed in terms of the steric requirements of the species and of the different donor properties of the solvents. ³¹P-{¹H} and ¹H NMR studies and FT-IR investigations have also been performed to obtain additional information on the nature of the species in solution.