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

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.