(C3H6O2)2(SI6O12)2, A NEW SILICA SODALITE SYNTHESIZED, USING 1,3-DIOXOLANE AS TEMPLATE

A clathrasil with SOD structure has been obtained using 1,3-dioxolane as a template. The synthesis was achieved under hydrothermal conditions at temperatures between 423 and 433 K in the SiO2-Na2O-C3H6O2-H2O system. The choice of the template was guided by stereochemical comparisons with the templates known for silica sodalite synthesis, ethylene glycol and 1,3,5-trioxane. The powder X-ray diffraction (XRD) measurement of dioxolane silica sodalite (C3H6O2)2(Si6O12)2 showed the typical pattern of silica sodalites with sharp, discrete reflections indicating high crystallinity. Indexing and refinement of the diffraction pattern gave a body-centered cubic unit cell with a lattice constant a0 = 8.868 (1) angstrom at room temperature, which is significantly larger than previously found in other silica sodalites. The value of a0 agrees with the Si-O-Si bonding angle derived from the position of the Si-29 NMR signal. Infrared (IR) and H-1, C-13 nuclear magnetic resonance (NMR) spectroscopic data are in agreement with dioxolane molecules occluded in a porous matrix. The weight loss during thermal analysis in an oxygen atmosphere shows that within the limits of the method each sodalite cage is occupied by one 1,3-dioxolane molecule. Differential scanning calorimetry (DSC) between 120 and 470 K reveals a reversible, temperature-induced phase transition at 271 K.