TWO NEW SILICA SODALITES - PYS-SOD, ETS-SOD Synthesis and Structure Analysis

Ulrike Werthmann, Bernd Marler, Hermann Gies

Institut für Mineralogie, Ruhr-Universität Bochum, Universitätsstr. 150, 44801 Bochum, Germany e-mail: Ulrike.Werthmann@ruhr-uni-bochum.de

Keywords: Silica sodalite, sodalite, clathrasil, Rietveld refinement, disorder

Introduction

Clathrasils are crystalline porous composite materials consisting of a silica framework with cage-like voids (host) and organic molecules (guest), which interact only via weak van der Waals forces. The framework of sodalite is built from only one polyhedron: the sodalite cage (Fig.1). Silica sodalite is cubic with a ~ 8.8 Å.

For the hydrothermal synthesis of sodalite type materials a neutral guest molecule is added as a structure directing agent (SDA). So far, six different silica sodalite materials are known which contain different SDAs as guest species [1,2,3,4]. New synthesis concepts now led to the crystallization of two new silica sodalites.

Results and discussion

PYS-SOD (pyrrolidin silica sodalithe): Using the "dry synthesis fluoride route" [5] cubo-octahedral crystals were obtained in the system SiO2/pyrrolidin/NH4F in sealed silica glass tubes at 160°C. The material was characterisized by optical microscopy, SEM, 13C-NMR-spectroscopy and single crystal structure analysis. PYS-SOD crystallizes in space group I 3m (no. 217) with the lattice parameter a = 8.8843(2) Å. The refinement (RF = 0.023 and Rw = 0.020) confirmed the typical sodalite cage and showed the pyrrolidin molecule to be dynamically disordered within in the cage. This is in accordance with results of other silica soldalites which also contain the guest molecule disorderd.

ETS-SOD (ethylamine silica sodalithe): Using a very high concen-tration of ethylamine (SiO2/ ethylamine/H2O = 1:13:14) small cubic crystals (20 mm) of ETS-SOD were synthesized in silica glass tubes at 160°C. IR-spectroscopy proved the presence of ethylamine in the structure. A Rietveld-Analysis in the space group I 3m (no. 217) led to the residuals of RF = 0.032, Rwp = 0.056 and c2 = 2.1. The smaller a value of ETS-SOD (a = 8.8462(1) Å) compared to PYS-SOD is due to the smaller size of the guest molecule. During the structure refinement the C- and N-Atoms of the dynamically disordered ethylamine were best simulated by 1 C-site at the position of the highest peak of the difference electron density map (6 C-atoms per cage with a occupation factor of 0.722).

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