A new silicate clathrate hydrate: An X-ray diffraction and nuclear magnetic resonance study of a system with octameric silicate anions and trivalent cations

The first crystal structure is reported for a silicate clathrate hydrate involving a triply charged cation [C18H30N3](3+) and an octameric cubic silicate cage. The structure is essentially a host/guest system, with the silicate cages linked into a framework by hydrogen bonding to water molecules. The space group is <P(1)over bar> with Z = 2, and the asymmetric unit includes a complete cation and half the anion, plus 21 water molecules (4 of which are in disordered positions). Solid-state (CPMAS) Si-29 and C-13 NMR spectra are consistent with the diffraction-determined structure and indicate substantial distortion of the anion from cubic symmetry. Solution-state spectra of precursor solutions and of melted material are also presented and discussed. (C) 1995 Academic Press, Inc.