The Ba–Co and Ba–Zn heterometallic 3D-polymers [BaM(H 2 O) 5 (Me 2 mal) 2 ] n , where Me 2 mal 2− is the dimethylmalonic acid dianion, M II =Co (1), Zn (2), were synthesized by the reactions of CoSO 4 or Zn(OAc) 2 , respectively, with Ba(OH) 2 in water. The thermal dehydration of 1 and 2 occurs in one step. A kinetic model for the dehydration of complexes 1 and 2 is proposed. Crystalline BaCoO 3− x and BaZnO 2 were formed as a result of solid state thermolysis of 1 and 2 under the following conditions: air flow rate 60ml/min, heating rate 10°C/min up to t=800°C (1) or 750°C (2), followed by storage for 12h at the same temperatures.