AKIYAMA Yoshikatsu    Department   Research Institutes and Facilities, Research Institutes and Facilities    Position   Assistant Professor
Article types	Original article
Language	English
Peer review	Peer reviewed
Title	Crystal Structure of a Helix Layered Silicate Containing Tetramethylammonium Ions in Sodalite-Like Cages
Journal	Formal name：Chemistry of Materials Abbreviation：Chem. Mater ISSN code：0897-4756 /1520-5002
Domestic / Foregin	Foregin
Publisher	American Chemical Society
Volume, Issue, Page	13(4),pp.1286-1295
Author and coauthor	IKEDATakuji, AKIYAMAYoshikatsu, IZUMIFujio, KIYOZUMIYoshimichi, MIZUKAMIFujio, KODAIRATetsuya
Authorship	2nd author
Publication date	2001/03/13
Summary	The crystal structure of a helix layered silicate (HLS), [(CH3)4N]2Na2[Si10O20(OH)4]·5.53H2O, with tetramethylammonium (TMA) ions as templates was determined by ab initio structure analysis with X-ray powder diffraction data. The HLS is orthorhombic with space group Amm2 and lattice parameters of a = 22.8641(2) Å, b = 12.5388(2) Å, and c = 12.4648(2) Å. A Q3−Q4−Q3 silicon network with an amount-of-substance ratio of Si/O = 1:2.4 exhibits cup-shaped cage topology with four- and six-membered rings. Such a cage is similar to a sodalite cage divided into two pieces. 29Si MAS NMR showed the silicate layer to have Q3- and Q4-types of Si atoms with a Q3/Q4 ratio of ca. 4.0, which is consistent with our structural model. The framework is distorted, with Si−O bond lengths varying widely. TMA ions are incorporated into the cup-shaped cage. Na+ ions and H2O molecules are also located between two silicate layers, with interlayer distances varying alternately. Disordering of TMA ions, Na+ ions, and H2O molecules was clearly visualized in electron-density maps obtained by combining a maximum-entropy method and whole-pattern fitting. H2O molecules surround Na+ ions and form hydrogen bonds with O atoms in silanol groups in the silicate layers, by which the lattice instability due to the distorted framework is compensated. The present compound is regarded as a metastable phase, as would be expected for precursors to new types of microporous materials with silicate frameworks such as the sodalite cage.
DOI	https://doi.org/10.1021/cm000736v
URL for researchmap	https://researchmap.jp/y_akiyama