Solid-state thermal decomposition of heterobimetallic oxalate coordination compounds, zinc(II)tetraaquatris(oxalato)lanthanate(III)hexahydrate and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate

摘要

Two heterobimetallic oxalate coordination compounds, zinc(II) tetraaquatris(oxalato)lanthanate(III)hexahydrate (ZnOLa) and cadmium(II)heptaaquatris(oxalato)lanthanate(III)tetrahydrate (CdOLa) were synthesized and characterized by elemental analysis, IR, electronic spectral and powder X-ray diffraction studies. Both the compounds were found to have monoclinic structure. Thermal decomposition studies by TG, DTG and DTA in air have proved that the aqua ligands are associated with metals in a stronger coordination mode. The temperatures for pyrolysis were adopted from the TG results chosen from the stable range of thermograms. In case of ZnOLa, it decomposes through two steps and the end product at 1000 C was found to be consisting of mainly, La_2O_3, ZnO and La_2ZnO _x through the intermediate formation of several oxycarbonates of lanthanum at ca. 525 C. In case of cadmium analogue, three steps decomposition were observed and the final products were confirmed as CdO_2, La _2O_3, LaCO and La_2CdO _x via the formation of several intermediates at 340 and 590 C. The La_2C _3 and carbon are also found as part of the end product. The kinetic parameters, E *, lnk _o, a??H ~# and a??S ~# of all the deaquated and decomposition steps are investigated and discussed from the DSC study in nitrogen.