New sodalite frameworks; synthetic tugtupite and a beryllosilicate framework with a 3 ? 1 Si ? Be ratio

Compounds of the formula Na8[Si(6 +y)Be(y)Al(6 - 2y)O24]X2, with X = Cl and Br, and y = 1, 2 and 3 have been synthesised and structurally characterised by combined powder X-ray and neutron diffraction profile analysis. These materials adopt the sodalite framework (SOD) with the tetrahedral species, BeO4, AlO4 and SiO4, disordered across the framework positions. Na8[Si8Be2Al2O24]Cl2, (y = 2), is a synthetic analogue of the naturally occurring semi-precious gemstone tugtupite, while Na8[Si9Be3O24]X2, X = Cl and Br represents a new tetrahedral framework stoichiometry with a Si ratio Be ratio of 3 ratio 1. Additional characterisation using 29Si MASNMR, IR spectroscopy and high-temperature, neutron diffraction show that the observed structure-property trends found when modelling sodalite materials can be extended to these new framework compositions.