Silver(I) Complex Formation with Phosphorus Donors in Propylene Carbonate. A Thermodynamic and Spectroscopic Investigation

The thermodynamics of complex formation between silver(I) and PPh3, bis(diphenylphosphino)methane (dppm), 1,2-bis(diphenylphosphino)ethane (dppe) and 1,3-bis(diphenylphosphino)propane (dppp) has been investigated in propylene carbonate at 298 K and 0.1 mol dm-3 ionic strength (NEt4ClO4) by potentiometric and calorimetric techniques. Within the silver(I) concentration range investigated, PPh3 forms three successive mononuclear complexes, dppm only polynuclear species, whereas mononuclear complexes, in addition to polynuclear ones, are formed by dppe and dppp. The thermodynamic data show that all complexes are stabilized by exothermic terms, the entropy changes being negative. In the mononuclear complexes, dppe and dppp act as chelating agents while in the very stable [Ag2L2]2+ species all the diphosphines behave as bridging ligands. These conclusions have been confirmed by P-31 NMR studies on solutions of silver(I). Comparison of the thermodynamic data for formation of the silver(I) complexes with the same ligands in dimethyl sulfoxide (dmso) show that the complexes are considerably weaker in dmso, mainly reflecting the stronger solvation of Ag+ in dmso with respect to propylene carbonate.