Synthesis and crystal structure of tetramethylammonium fluoride octadecasil

Journal Article · Thu Jan 05 04:00:00 EST 2006 · Materials Research Bulletin

DOI:https://doi.org/10.1016/j.materresbull.2005.07.040· OSTI ID:20891598

Xiaobo, Yang ^[1]

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1. Institute of Physical Chemistry and Electrochemistry, University of Hanover, D-30167 Hanover (Germany)

Octadecasil, a clathrate-type inclusion compound, has been synthesized hydrothermally at 453 K with a gel having the composition 1.0SiO{sub 2}:0.53tetramethylammonium (TMA{sup +}):0.54fluoride:86H{sub 2}O. The crystal structure has been determined based on powder X-ray diffraction data taken at 298 K, and has been refined using Rietveld method. The result confirms the AST-type, all-silica framework model developed by Caullet et al. [P. Caullet, J.L. Guth, J. Hazm, J.M. Lamblin, H. Gies, Eur. J. Solid State Inorg. Chem. 28 (1991) 345]. Furthermore, by using a rigid body model the position and orientation of the occluded TMA{sup +} cation in the rhombododecahedral [4{sup 6}6{sup 12}] cage can be determined; F{sup -} anion has been located in the hexahedral [4{sup 6}] cage. The unit cell parameters, in the tetragonal space group I4/m, have been refined as: a = b = 9.07 A, c = 13.44 A, cell volume = 1104.97 A{sup 3}. The refined unit cell composition is |[N(CH{sub 3}){sub 4} {sup +}]{sub 2.0}F{sup -} {sub 1.9}|[Si{sub 20}O{sub 40}], i.e., both TMA{sup +} and F{sup -} ions possess near full occupancies, and compensate each other's electronic charges. The crystallization of the AST framework structure is the result of a cooperative structure-directing effect of both ions.

• OSTI ID: 20891598
• Journal Information: Materials Research Bulletin, Journal Name: Materials Research Bulletin Journal Issue: 1 Vol. 41; ISSN MRBUAC; ISSN 0025-5408
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BUILDING MATERIALS
CLATHRATES
CRYSTALLIZATION
FLUORIDES
FLUORINE IONS
GELS
METHYL RADICALS
POWDERS
SILICA
SPACE GROUPS
TETRAGONAL LATTICES
X-RAY DIFFRACTION