Isostructurality and Thermal Properties in the Series of Double Complex Salts [M1(NH3)6][M2(C2O4)3]·3H2O (M1 = Co, Ir, M2 = Fe, Cr)

Abstract

A series of four isostructural double complex salts are prepared on the basis of [M¹(NH₃)₆]³⁺ cations and [M²(C₂O₄)₃]^3– anions, where M¹ = Co, Ir, M² = Fe, Cr. The salts are crystallized in a hexagonal space group P3̄c1. According to thermal analysis data, thermal stability in an atmosphere of argon (starting temperature of the decomposition of dehydrated products) of studied compounds depends on the nature of the complex tris-oxalate anion and increases in the series [M¹(NH₃)₆][Co(C₂O₄)₃] < [M¹(NH₃)₆][Fe(C₂O₄)₃] < [M¹(NH₃)₆][Cr(C₂O₄)₃] < [M¹(NH₃)₆][Ir(C₂O₄)₃] (M¹ = Co, Ir). Hexammineiridium(III) salts are more stable than cobalt(III) salts with the same anion. Thermal decomposition of [Co(NH₃)₆][Fe(C₂O₄)₃]·3H₂O and [Ir(NH₃)₆][Fe(C₂O₄)₃]·3H₂O salts in an atmosphere of hydrogen leads to the formation of solid solutions Co_0.5Fe_0.5 and Ir_0.5Fe_0.5, respectively.