SINGLE-CRYSTAL X-RAY-DIFFRACTION AND VARIABLE-TEMPERATURE MAS NMR-STUDY ON THE HETEROGENEOUS NETWORK CLATHRATE NA[N(CH3)4]7[SI8O20].54H2O

Crystal data: M(r) = 2059.54, trigonal, R3BAR, a = 21.374 (3), c = 19.769 (2) angstrom, V = 7821.2 angstrom3, Z = 3, D(x) = 1.31 Mg m-3, lambda(Mo K-alphaBAR) = 0.71073 angstrom, mu = 0.21 mm-1, F(000) = 3372, T congruent-to 190 K, R = 0.078 for 2534 unique observed reflections. The host-guest compound consists of a three-dimensional four-connected network composed of hydrogen-bonded oligomeric silicate anions with double four-ring structure, [Si8O20]8-, and H2O molecules. This mixed (heterogeneous) network has the topology of net No. 214 and zeolite-structure type AST. Orientationally disordered cationic guest species NMe4+ are enclosed in large [4(6)6(12)] octadecahedral cages of Na[NMe4]7{infinity/3}[{2r}[(Si8O20][H2O]54]-Si-4. Positional disorder of some H2O molecules is induced by Na+ cations which statistically occupy 1/6 of small [4(6)] cages with H2O at their comers, as deduced from structure-chemical considerations supported by Na-23 MAS NMR spectra. The Si-29 MAS NMR spectrum shows two resonance lines in agreement with the double-ring structure and site symmetry 3BAR of the silicate anion. The C-13 NMR chemical shift depends on the environment (polyhedral cage) around the NMe4+ cations. H-1, C-13 and Na-23 MAS NMR spectra at various temperatures between 170 and 320 K indicate rapid motions of NMe4+, H2O and probably Na+ on the NMR time scale at room temperature which become reduced when the temperature is lowered. The close structural relationship to the heterogeneous network clathrate [NMe4]4{infinity/3}[{2r}[Al4Si4O12(OH)8][H2O]24]-Al-4 is discussed.