Thermal studies on the dimesoperiodates and iodates of Ca(II), Sr(II) and Ba(II) preparation and characterization of hexavalent iodates

Abstract

The dimesoperiodates of the alkaline earths, M₂I₂O₉. nH₂O (Ca, n = 8; Sr and Ba, n = 3) on thermolysis form hexavalent iodates, MIO₄ as intermediate products which with increasing temperature decompose to their orthoperiodates, M₅(10₆)₂ via presumably the formation of M₂I₂O₇ type compounds. MIO₄ compounds can be made from dimesoperiodates by heating at 220-240° for 2 hr. The hexavalent state of iodine in MIO₄ has been verified by chemical analysis, magnetic moment measurement and EPR spectra. These compounds undergo hydrolytic decomposition to metal iodate and hydroxide accompanied by the evolution of oxygen. Anhydrous barium iodate prior to its decomposition undergoes a phase transition, this change is less defined in the strontium compound and is not observed in calcium iodate. The energy of activation, the order of reaction and the enthalpy change for the conversion of the iodates to the orthoperiodates have been evaluated by non-isothermal kinetic study.