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

Abstract

Compounds of the formula Na₈[Si_{6 + y}Be_yAl_{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 ∶ Be ratio of 3 ∶ 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.