Decomposition of Mg(HSeO3)2x3H2O and Mg(HSeO3)2, IR spectroscopic and thermoanalytical investigations

By crystallization from aqueous Mg(HSeO3)2 solutions, single cristals of Mg(HSeO3)2x3H2O, Mg(HSeO3)2, and MgSe2O5 could be obtained. The compounds have been characterized by means of IR spectroscopy. The dehydration mechanisms of Mg(HSeO3)2x3H2O and Mg(HSeO3)2 have been studied using TG, DTA and high-temperaure Raman techniques. DTA and TG measurements indicate that the thermal decomposition of Mg(HSeO3)2x3H2O results in the direct formation of the diselenite MgSe2O5. High-temperature Raman experiments under quasi static conditions (heating rate<5K/h, isothermal intervals of -1h) show that Mg(HSeO3)2x3H2O decomposes in two steps under the intermediate formation of the anhydrous hydrogenselenite Mg(HSeO3)2.