INTERMEDIATES IN THE THERMAL-DECOMPOSITION OF NORMAL COPPER(II), NICKEL(II) AND COBALT(II) SELENITE DIHYDRATES

Thermal decomposition of normal transition metal selenite dihydrates, MSeO(3) . 2H(2)O; M = Cu(II), Ni(II), Co(II) was traced by TGA/DTA mea surements from 50-700 degrees C. The thermal products were obtained by heating the selenites in an air-oven to different temperatures, as de termined from TGA/DTA curves, where different coloured products are ob tained. The structures of the start selenites and the thermal intermed iates were determined by chemical analyses and FT-IR spectral measurem ents. The start selenites proved to be equilibrium mixtures of the sel enite, hydrogenselenite and/or pyroselenite anions. Gradual changes oc curred in the FT-IR spectra of the nickel and cobalt selenites on ther mal treatment till 225 degrees C where, due to water loss, merely sele nite anions are observed. in the case of the copper selenite, the sele nito mixture persists till 250 degrees C and the only change observed in the final product is the disappearance of one of the structurally n on-equivalent water molecules present in the start selenite dihydrate.