X-Ray diffraction and solid-state nuclear magnetic resonance study of a silicate containing two different nitrogenous cations

Abstract

Single-crystal X-ray diffraction has been used to determine the structure of a silicate hydrate containing both the tetraethylammonium cation and a cation containing three nitrogen atoms. The structure is monoclinic, space group C2/c, and may be regarded as a host–guest system, with the cations as guests in a hydrogen-bonded framework consisting of a cubic octameric silicate anion, [Si₈O₂₀]^8–, and water molecules. Magic-angle spinning ¹³C, ²⁹Si and ¹H NMR spectra are consistent with the crystallographic asymmetric unit. The precursor solution, the mother-liquor after crystallisation, and the solution obtained by melting the crystals have also been examined by NMR spectroscopy. The implications for silicate solution equilibria and for zeolite synthesis mechanisms are discussed.