Structural studies on preferential solvation of silver(I) ion by acetonitrile over N,N-dimethylformamide in their mixtures

The solvation structure of the silver(I) ion in neat N,N-dimethylformamide (DMF), neat acetonitrile (AN) and their mixtures has been determined by the X-ray diffraction method at 25 degrees C. In neat DMF and AN, the silver(I) ion forms the tetrahedral [Ag(dmf)(4)](+) and [Ag(an)(4)](+) complexes with the Ag-O and Ag-N bond lengths of 233(1) and 226(1) pm, respectively. The tetrahedral [Ag(dmf)(2)(an)(2)](+) complex is the predominant species in 3:1 and 2:1 DMF:AN molar mixtures. In the 1:2 DMF-AN mixture, the tetrahedral [Ag(dmf)(an)(3)](+) complex is formed as the main species. The silver(I) ions are present as an equilibrium mixture of [Ag(dmf)(2)(an)(2)](+) and [Ag(dmf)(an)(3)](+) (ca. 1:1) in the 1:1 DMF-AN mixture. Thus, a preferential solvation of the silver(I) ion by AN occurs in DMF-AN mixtures, as expected from their solvation energies in each solvent. The Ag-O bond length in the [Ag(dmf)(2)(an)(2)](+) and [Ag(dmf)(an)(3)](+) complexes is 237(3) and 241(3) pm, respectively, and increases with the number of AN molecules within the complexes. On the other hand, the Ag-N bond length remains practically unchanged by the coordination of DMF molecules;224(2) pm in [Ag(dmf)(2)(an)(2)](+) and 224(1) pm in [Ag(dmf)(an)(3)](+).