Thermal decomposition of [Co(NH₃)₆][Fe(C₂O₄)₃]∙3H₂O in argon atmosphere, at a low heating rate (3°/min), and in large amounts of the initial complex (~0.1 mole), has been studied. It was possible to distinguish four decomposition steps upon heating: In the temperature range of 50–100 °C—the loss of crystal water; 100–190 °C—stability region of dehydrated complex; 230–270 °C—the range of stability of intermediate phase with the formula CoFe(NH₃)₂(C₂O₄)₂; 270–350 °C—thermal decomposition of the intermediate with the formation of metallic products and further air oxidation with the formation of Co_1.5Fe_1.5O₄. Catalytic properties of thermolysis products were tested in the decomposition reaction of H₂O₂ (inactive), oxidation of acetone (average activity), and decomposition of ammonium perchlorate (highly active).

This review deals with the thermal behavior of cationic, anionic, and double complex compounds of 3d-metals (Fe, Co, Ni, Cu, Mn, and Cr) in comparison with complexes of noble metals, with coordinated ammonia, organic amines, urea, cyanide, thiocyanate, oxalate, and nitrite. It is shown that in the thermolysis process carried out under non-equilibrium conditions, double complexes can withstand heating up to 200–250°C, regardless of their thermodynamic stability.

The current state of studies on binary complex compounds [M¹L _a ] _x ·[M²A _b ] _y (M¹ and M² are the central ions, L and A are ligands) is considered, notably: synthesis, composition, structures, magnetic properties, and thermal decomposition.

Binary complexes [Co(A)₆][M(C₂O₄)₃] (A = NH₃, 1/2C₂H₈N₂, M = Fe, Cr) are synthesized, and their physicochemical properties and thermal decomposition in air, argon, and hydrogen are studied. The qualitative and quantitative analyses are carried out for the solid and gaseous thermolysis products. Similar regularities are revealed in the behavior of complexes [Co(NH₃)₆][Fe(C₂O₄)₃] (I), [Co(En)₃][Fe(C₂O₄)₃] (II), [Co(NH₃)₆][Cr(C₂O₄)₃] (III), and [Co(En)₃][Cr(C₂O₄)₃(IV). The solid thermolysis product for complexes I and III in argon at 225 and 300°C is Co(NH₂)₂M(C₂O₄)₂, respectively; and that for complexes II and IV at 280 and 380°C is Co(En)₂M(C₂O₄)₂. The gaseous thermolysis products are CO and CO₂, NH₃, En partially isolated upon thermal destruction, other products of En destruction, and En itself. Complex III forms the most highly dispersed solid products in a range of 300–400°C.

The complexes [Ni(Pn)2]2[Fe(CN)6] · 3H2O ( I), [Ni3(Pn)5][Fe(CN)6]2 · 9H2O ( II), [Ni5(Pn)9][Fe(CN)6]3 · 9H2O ( III), and [Ni(Pn)2]3[Fe(CN)6]2 · 6H2O ( IV) (Pn = 1,3-diaminopropane) were obtained....