Thermal Stability of Mixed Fluorides of 3 d Elements

Literature data on the existence of mixed fluorides of 3 d elements M(II)M(III)F 5 (M = Mn, Fe, Co, Ni) were analyzed. Heterogeneous equilibria in MF 2 –MF 3 systems were considered, and equilibrium constants and enthalpies were calculated for the reactions with participation of M 2 F 5 (c). The FeF 2 sublimation enthalpy of 268.7 ± 1.9 kJ/mol was confirmed, and the FeF 3 (c) sublimation enthalpy was essentially refined, equal to 264.5 ± 2.2 kJ/mol. For crystalline fluorides Mn 2 F 5 , Fe 2 F 5 , Co 2 F 5 , and Ni 2 F 5 , the standard formation enthalpies were determined as equal to –1909.0 ± 7.8, –1716.3 ± 4.4, ≥–1554.2 ± 11, and –1370.5 ± 8.0 kJ/mol, respectively, at 0 K. The enthalpies and Gibbs energies of formation of these compounds from crystalline MF 2 and MF 3 were within a range of values typical for the solid solutions with weak interaction.