Double complex salts (DCSs) [Co(NH3)6][Fe(CN)6] (I) and [Co(NH3)6]2[Cu(C2O4)2]3 (II) and complex [Co(NH3)6]2(C2O4)3·4H2O (III) are synthesized and investigated by single crystal XRD, crystal optics, and elemental analysis. The crystalline phases of I, II, and III (R-3, P21/c, and Pnnm space groups respectively) have the following crystallographic characteristics: a = 10.9804(2) Å, b = 10.9804(2) Å, c = 10.8224(3) Å, V = 1130.03(4) Å3, Z = 3, d x = 1.65 g/cm3 (I); a = 9.6370(2) Å, b = 10.2452(2) Å, c = 13.2108(3) Å, V = 1932.90(9) Å3, Z = 2, d x= 1.97 g/cm3 (II), and a = 11.7658(3) Å, b = 11.7254(3) Å, c = 14.1913(4) Å, V = 1304.34(5) Å3, Z = 2, d x = 1.68 g/cm3 (III). This paper investigates the products of DCS thermolysis in a hydrogen atmosphere: the intermetallic compound CoFe with the bcc parameter a = 2.852 Å for I and a heterogeneous mixture of Co and Cu in the decomposition of II. The coordinated CN− and C2O 4 2− groups then turn into NH3, hydrocarbons, and CO2. The dominant hydrocarbon is methane.