Intracage reactions in sodalites

Abstract

Sodalites containing thiocyanate [Na₈(AlSiO₄)₆(SCN)₂·xH₂O] and nitrite [Na₈(AlSiO₄)₆(NO₂)₂·xH₂O] have been synthesised by precipitation from aluminosilicate solutions at low temperature. Cation-exchange reactions in aqueous solution were undertaken on the thiocyanate material to afford the fully substituted silver and lithium analogues. The mild and low-temperature conditions under which cation exchange occurs contrast markedly with similar, previously described reactions on this family of compounds involving melts and direct reaction between solids at 300–800 °C. These compounds undergo slow intracage oxidation reactions of the anions on heating in air to yield sodalites containing OCN^–,S_x^–, and SO₄^2– from SCN^– and NO₃^– from NO₂^–. The extent and direction of these oxidation reactions depends upon the nature of the cation also present in the cage. The products of these indirect syntheses have been characterised by power X-ray and neutron diffraction, i.r. and u.v.–visible spectroscopy, and thermogravimetric analysis.