abstract
Sodium chloride stannosilicate AV-13 (Na2.26SnSi3O9Cl0.26.xH(2)O) and zirconium and hafnium analogues of this material have been prepared and their structures solved from powder X-ray diffraction data using direct methods, and Na-23, Si-29 and Sn-119 solid-state NMR. AV-13 materials are small-pore solids, probably more adequately described as tunnel structures. The AV-13 framework consists of corner-sharing MO6 (M = Sn, Zr, Rf) octahedra and SiO4 tetrahedra. The latter form six-membered [Si6O18](12-) rings, which are interconnected by MO6 octahedra. The structure is better understood by considering a three-dimensional knots- and-crosses lattice. In a given layer, successive distorted-cube M-8 cages contain [Na6-x(H2O)](H2O,Cl-) octahedra (knots) and cyclohexasilicate (crosses) units. While the former are extra-framework species, the six-membered rings are, of course, part of the framework. The cages are accessed via seven-membered [M3Si4O27](26-) windows, with free aperture ca. 2.3 x 3.2 Angstrom, one per each pseudo-cube face. Pilling up layers generates the structure, with knots-and-crosses alternating. The non-framework five-coordinated Na cations are disordered. (C) 2003 Elsevier Science B.V. All rights reserved.
keywords
CRYSTALLINE INORGANIC SOLIDS; MOLECULAR-SIEVES; FRAMEWORK; STANNOSILICATES; EXCHANGE; OXIDES
subject category
Chemistry
authors
Ferreira, A; Lin, Z; Soares, MR; Rocha, J
our authors
Artur Jorge Faria Ferreira
Professor Coordinator
João Rocha
Full Professor
Maria do Rosário Teixeira Soares
Laboratory Officer