On the thermal decompositions of the trivalent trioxalato complexes of Al, Cr, Mn, Fe and Co

The thermal decompositions of the complexes K3[M(ox)3]·3H2O (M=Al, Cr, Mn, Fe, Co; ox=C2O42) were studied. Dehydration of the complexes occurs up to 200°C, this being a three-step process for M=Al, Cr, Mn and Co, and a two-step process for M=Fe. Decomposition of the dehydrated complexes proceeds in several steps. For M=Al, Cr and Fe, the decomposition takes place with the evolution of CO, whereas for M=Mn and Co the decomposition of the oxalate ligand yields solid C besides CO. The temperature of CO liberation decreases in the series Cr<Al<Co<Mn<Fe. For M=transition metal, this trend can be explained by the fact that the strength of the C-C bond in the oxalate ligand decreases in the series Cr<Co<Mn<Fe.