Double complex compounds (DCC) of the [Cr(ur)₆][Fe(CN)₆]^·4H₂O (I), [Cr(ur)₆][Co(CN)₆]·4H₂O (II), [Cr(ur)₆][Fe(Ox)₃]·2H₂O (III), and [Cr(ur)₆][Co(Ox)₃].3.5H₂O (IV) composition, where ur is CO(NH₂)₂, Ох – С₂О₄ ²⁻ have been synthesized and their crystal structures have been studied. The DCC I, II and IV are triclinic (Р-1); III is orthorhombic (С222₁). The DCC thermal behavior in air and argon atmospheres was analyzed by the following parameters: the temperature interval of total decomposition and the nature of gaseous and solid products. The end solid products in air were FeO and FeCr₂O₄ for I, a mixture of СоCr₂O₄ + Со₂CrO₄ for II and IV and an X-ray amorphous phase with composition CrFeO_2.5 for III. The gaseous products were HCN, NH₃, HNCO, N₂O, СО, СО₂, N₂, and urea. The temperatures of total decomposition in air were: I, II 400°С, III – 350°С, IV – 460°С. In argon, the solid residue contained, besides the oxides, 7–30% of carbon up to 1000°С.