Spectrochemistry of solutions. Part 14. Raman and infrared spectra of thiocyanatosilver(I) complexes in some non-aqueous solutions

Abstract

Infrared and Raman spectra have shown that, when Ag⁺ is complexed by SCN^–, the species present and the equilibrium steps involved are solvent specific. In pyridine, complexation of Ag⁺ by SCN^– passes through [Ag₂(SCN)]⁺ and AgSCN to [Ag(SCN)₂]^–. Only AgSCN and [Ag(SCN)₂]^– have been identified in tetrahydrofuran, dimethyl sulphoxide, and acetone, and only [Ag(SCN)₂]^– was found in propylene carbonate. Solutions in dimethylformamide and dimethylacetamide at high [SCN^–]/[Ag⁺] ratios contain a small proportion of the SCN^– in the bridged complex [Ag₂(SCN)₃]^–, but in trimethyl phosphate the SCN^– is approximately equally distributed between [Ag₂(SCN)₃]^– and [Ag(SCN)₂]^–. The spectra of thiocyanatosilver(I) complexes in hexamethylphosphoramide differ from those of all the other solutions; no linear [Ag(SCN)₂]^– complex is found and two feasible explanations of the spectra are offered. No complex higher than [Ag(SCN)₂]^– occurs in any of these solutions.