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

Compounds of the formula Na[SiBe AlO]X, 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, BeO , AlO and SiO, disordered across the framework positions. Na[SiBeAl O]Cl, (y = 2), is a synthetic analogue of the naturally occurring semi-precious gemstone tugtupite, while Na [SiBeO]X, X = Cl and Br represents a new tetrahedral framework stoichiometry with a Si Be ratio of 3 1. Additional characterisation using Si 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.