The solid state isomerization and thermal decomposition of pentamminethiocyanatocobalt(III) salts [Co(NH₃)₅SCN] X₂ (X = Cl, SCN)

Abstract

Radiochemical tracer experiments show that in the thiocyanate complex, [Co(NH₃)₅SCN] [SCN]₂, thermal isomerization to the isothiocyanate salt proceeds with incorporation of anionic thiocyanate. At least 45% of the isomerization process proceeds by a dissociative path. This contrasts with the mechanism in water solution where isomerization occurs without exchange with thiocyanate in solution. The result also shows the inadequacy of the generally made assumption that isomerization in the solid state is an intramolecular process. The chloride and thiocyanate salt were subjected to simultaneous thermogravimetric analysis and differential scanning calorimetry. The thiocyanate salt deamminates at a much lower temperature (from 100ºC) than the chloride (from 160ºC), but no process corresponding to the isomerization could be detected.