Fehlordnung von Kationen und Kristallwasser bei kubischen Alkalitetrabromo- und -iodothallaten(III)/Disorder of Cations and Water Molecules in Cubic Tetrabromo- and -iodothallates

Abstract

Abstract Tetrabromo- and -iodothallates(III) of the alkali cations crystallise from aqueous solutions as cubic hydrates MTlX4·nH2O (M = Li, Na, K, Rb, Cs, NH4; X = Br, I; n = 1-2). The tetraiodothallates retain their cubic structure on dehydratisation, while the tetrabromothallates undergo structural changes. The X-ray structure analyses of RbTlBr4 · H2O, NH4TlBr4 · 2H2O and KTlBr4 · 2H2O (-50 °C) showed that these compounds consist of a three-dimensional framework of TlBr4 tetrahedra and MBr12 ikosahedra which reminds of zeolites. In cavities of this framework 2/3 of the alkali cations and the crystal water molecules are accommodated in a disordered manner.