A mechanistic approach on the solid state thermal decomposition of bimetallic oxalate coordination compounds of Mn(II), Fe(II) and Cu(II) with cobalt

The mixed metal carboxylates, manganese(II)bis(oxalato)cobaltate(II)hydrate (MOC), iron(II)bis(oxalato)cobaltate(II)pentahydrate (IOC), and copper(II)bis(oxalato)cobaltate(II)trihydrate (COC) have been synthesized and characterized by elemental analysis, IR spectral and X-ray powder diffraction studies. Thermal decomposition studies (TG, DTG and DTA) in air showed that the compound MOC decomposed mainly to MnCOO3 at 315 degrees C through the formation of a complete anhydrous compound. The species CoFeO3 is generated at 274 degrees C from the compound IOC through the formation of a very transient anhydrous compound at around 218 degrees C. In case of the compound, COC the end product was found to be CuCoO2 at similar to 1000 degrees C through the existence of a quite stable mixture of CuO and COO at similar to 318 degrees C. DSC studies in nitrogen indicated the formation of a mixture of MnO and COO in case of MOC, cobalt ferrite in case of IOC and a brown mixture of Cu2O and COO from COC as end products. The kinetic parameters have been evaluated for both the dehydration and decomposition steps of all the three compounds using four non-mechanistic equations. Using seven mechanistic equations, the rate controlling processes of the dehydration and decomposition mechanism are also inferred. The kinetic parameters, Delta H and Delta S obtained from DSC are presented. IR and X-ray powder diffraction studies identified some of the decomposition products. (c) 2006 Elsevier B.V. All rights reserved.