An exchange reaction between Ba[RuNO(NO2)4OH] and cobalt (nickel) sulphate results in the formation of heterometallic [RuNO(NO2)4OHM(H2O)3] complexes with bridging (N,O)-NO2 and μ-(OH) ligands. The crystal structures of both complexes are determined. Thermal decomposition in H2/He atmosphere leads to the formation of solid solutions of the metals. In the case of the nickel complex, the compositions of the prepared solid solutions are in the miscibility gap. In oxygen atmosphere mixed oxide systems NiO–RuO2 and Co3O4–RuO2 are formed in temperature interval from 400 to 600 °C. At temperatures from 900 to 1000 °C spinel-type phase Co2.1Ru0.9O4 is formed.