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.