Structural-chemical studies of novel sodalites and related materials

Wong, Gordon (1989) Structural-chemical studies of novel sodalites and related materials. University of Southampton, Doctoral Thesis.

Abstract

Aluminosilicate sodalites M₈(AISiO₄)₆X₂, [M = Na, Li, K, Ag; X = Cl, Br, l, SCN, NO₂CrO₄, WO₄ etc] have been prepared by a solid-state structure conversion method and studied in terms of the compositional flexibility of the sodalite family. Ion exchange reactions have been performed using high temperature solid-state and low temperature methods to yield mixed cation derivatives. Materials have been characterised by powder X-ray and neutron diffraction (XRD,PND) at room temperature, and by thermogravimetric analysis (TGA) and A.C conductivity measurements. A low temperature solution method has also been used to prepare some hydrated phases of sodalitic as well as related cancrinitic structure. PND has confirmed previous structural refinement results for such materials, and a series of mixed cation sodalites has been characterised by PND for the first time showing a previously unreported movement of cage anion off the expected 2(a) site in P=43n. A new series of sodalites containing mixed halide cage species has been synthesised and studied by PND showing no evidence for halide ordering and no signs of superstructure behaviour. Sodalites containing both single and mixed metal types have been modelled by a geometrical technique and studied in terms of bond distance correlation behaviours. A study of intracage behaviour with temperature has been carried out on sodalites containing thiocyanate and nitrite. SCN-sodalites show decomposition of cage species to generate highly coloured polysulphide anions within the cavities while NO₂-sodalites display a slow in-cage oxidation of NO₂ to NO₃. Solid-state ²⁹Si MAS-NMR spectra were collected for the sodalites and show a resonance, assignable to Si-(OAI)₄ environments, which covers a much larger chemical shift range than previously reported for such a silicon coordination type. ²⁹Si chemical shift has been correlated with framework Si-O-Al bond angle determined from PND experiments. A series of hauynes isostructural with the sodalites has been prepared by high temperature solid state reaction and has been characterised by XRD. Compositional flexibility within the hauyne structure has been investigated. Materials containing complex anions (CrO₄^2-, SCN^-, S₂O₃^2-) have been subjected to structural studies for the first time. Na/CrO₄-noselite has been refined in space group P23 with cage CrO₄² groups arranged in a disordered fashion at room temperature while Na/SCN-sodalite and Na/S₂O₃-cancrinite have been refined in P=43n and P6₃ respectively; disordering at room temperature prevented accurate location of cavity SCN^- and S₂O₃^2- sites.

This record has no associated files available for download.

Contributors

Download statistics