RUB-23: a new microporous lithosilicate containing spiro-5 building units
Microporous and Mesoporous Materials 37(1-2): 129-143
A new microporous lithosilicate, Cs-10(Li,H)(14)[Li8Si40O96]. 12H(2)O, was synthesised under hydrothermal conditions. The crystal structure has been solved and refined from single-crystal data in the space group P2(1) to R=14%. The three-dimensional (3D) silicate framework contains lithium as cations on T sites in the centre of spiro-5 units that are charge-balanced by non-framework caesium, lithium and hydrogen cations. The hydrate water in the pores can be removed, and the structure is stable up to similar to 300 degrees C. The experimental density of the as-synthesised crystal is 2.62 g cm(-3); the framework density is calculated to be 17.7 T/1000 Angstrom. The channel system is one-dimensional for 10-membered ring (10-MR) channels which are connected to 8-MRs running parallel to the 10-MRs. The connection is established by 8-MR pore openings. In principle, this allows the 3D diffusion of (at least) small molecules. Chemical analysis, Si-29, Li-7 and Cs-133 solid-state nuclear magnetic resonance (NMR) spectroscopy, thermal analysis, infrared (IR) spectroscopy and X-ray structure analysis are all consistent and agree with crystal-chemical reasoning based on the flexibility of [TO4] units in silicates which are required to build 3-MRs as observed in spiro-5 units. (C) 2000 Elsevier Science B.V. All rights reserved.