Spectrochemistry of solutions. Part 5. —Raman spectroscopic study of the coordination of silver(I) ions in liquid ammonia by thiocyanate ions
Abstract
A detailed study of the Raman spectra of mixtures of AgNO3 and KSCN in liquid ammonia solution indicates the formation of a weak S-bonded 1:1 complex between Ag+ and SCN–. Formation constants (concentration quotients) are 3.1±0.5 and 1.3±0.4 kg mol–1 at 293 and 233 K respectively. The formation of AgSCN is entropy favoured (ΔS≃ 37 J mol–1 K–1) but enthalpy hindered (ΔH≃ 8.2 kJ mol–1); the equilibrium [Ag(NH3)4]++SCN–⇌[Ag(NH3)3SCN]+ NH3 is proposed on the basis of these results.
The possible existence of species such as [Ag2SCN]+ and [Ag(SCN)2]– is suggested by some minor spectral features.