Thermodynamic and spectroscopic studies on the complexation of silver(I) by mixed phosphorus–sulfur compounds in propylene carbonate. Crystal and molecular structure of a silver(I)–thiophosphine complex

Abstract

The thermodynamic parameters for complexation of silver(I) with the mixed-donor compounds Ph₂PCH₂SPh and Ph₂P(CH₂)₂SR (R = Me, Et or Ph) have been determined by potentiometric and calorimetric techniques in propylene carbonate at 25 °C and 0.1 mol dm^–3 ionic strength (NEt₄ClO₄). Within the silver(I) concentration range investigated, Ph₂PCH₂SPh forms three successive mononuclear complexes whereas also polynuclear species are formed by the other thiophosphines. All the complexes are strongly enthalpy stabilized, the entropy changes being unfavourable. The ligands behave as either monodentate (through P) or bidentate, depending upon the length of the aliphatic chain between the donor atoms and on the stoichiometry of the species formed. The influence of R on the stabilities of the complexes is discussed. The crystal structure of the 1 : 1 Ag–Ph₂P(CH₂)₂SEt complex has been determined: monoclinic, space group P2₁/c, a= 8.924(2), b= 9.620(1), c= 44.797(6)Å, β= 93.41(1)° and Z= 4. Phosphorus-31 NMR studies have also been performed to obtain additional information on the nature and structure of the species formed. Comparison of the thermodynamic data for formation of the silver(I) complexes with the same ligands in dimethyl sulfoxide evidences a different behaviour of the ligands in the two media: the results are discussed in terms of the different physicochemical properties of the two solvents.