Some heterobimetallic oxalate coordination precursors of lanthanum(III) of the type, M3[La(C2O4)3(H2O) m ]2•nH2O (M = Mn(II), Co(II), Ni(II) and Cu(II)) An investigation on the solid-state pyrolytic decomposition

Heterobimetallic oxalato complex precursors, manganese(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate (MnOLa), cobalt(II)pentaaquatris(oxalato)lanthanate(III)trihydrate (CoOLa), nickel(II)pentaaquatris(oxalato)lanthanate(III)hexahydrate (NiOLa) and copper(II)diaaquatris(oxalato)lanthanate(III)monohydrate (CuOLa) of the type, M-3[La(C2O4)(3)(H2O) (m) ](2)center dot nH(2)O have been synthesized in aqueous medium. The precursors were characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. The good crystalline nature with monoclinic structures predominates in MnOLa and NiOLa whereas triclinic structures were found in CoOLa and CuOLa. The solid-state thermal behaviour of the precursors was explored using TG, DTG and DTA in air. The MnOLa generated a mixture species consisting mainly of MnO2, Mn3O4, Mn5O8, La2O3 and LaMn7O12 at 1000 A degrees C through the formation of several intermediate species at 380 and 570 A degrees C. The studies revealed that CoOLa led mainly to LaCoO3 and La2CoO4 along with some oxides of both the cobalt and lanthanum at 1000 A degrees C. In case of nickel analogue the mixture species identified at 1000 A degrees C are mainly of La2NiO4, La2O3, Ni2O3 and NiO2. In case of CuOLa the product at 1000 A degrees C consisted of La2CuO4, La2Cu2O5 and oxides of copper and lanthanum. The nature of decomposition of the precursors in nitrogen were seen from DSC study and the kinetic parameters i.e., E (*) , lnk (0), Delta H (#) , Delta S (#) and order of reaction of all the steps were evaluated and discussed.