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Structural characterization of high-pressure C-Na2Si2O5 by single-crystal diffraction and 29Si MAS NMR

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Weidenthaler,  C.
Research Department Schüth, Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Zibrowius,  B.
Service Department Mynott (NMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society;

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Citation

Rakić, S., Kahlenberg, V., Weidenthaler, C., & Zibrowius, B. (2002). Structural characterization of high-pressure C-Na2Si2O5 by single-crystal diffraction and 29Si MAS NMR. Physics and Chemistry of Minerals, 29(7), 477-484. doi:10.1007/s00269-002-0259-1.


Cite as: http://hdl.handle.net/11858/00-001M-0000-000F-99B0-F
Abstract
Single crystals of C-Na2Si2O5 have been synthesized from the hydrothermal recrystallization of a glass. The title compound is monoclinic, space group P21/c with Z = 8 and unit-cell parameters a=4.8521(4)Å, b=23.9793(16)Å, c=8.1410(6)Å, β=90.15(1)° and V=947.2(2)Å3. The structure has been determined by direct methods and belongs to the group of phyllosilicates. It is based on layers of tetrahedra with elliptically six-membered rings in chair conformation. The sequence of directedness within a single ring is UDUDUD. The sheets are parallel to (010) with linking sodium cations in five- and sixfold coordination. Concerning the shape and the conformation of the rings, C-Na2Si2O5 is closely related to β-Na2Si2O5. However, both structures differ in the stacking sequences of the layers. A possible explanation for the frequently observed polysynthetic twinning of phase C is presented. In the 29Si MAS-NMR spectrum of C-Na2Si2O5 four well-resolved lines of equal intensity are observed at -86.0, -86.3, -87.4, and -88.2 ppm. The narrow range of isotropic chemical shifts reflects the great similarity of the environments of the different Si sites. This lack of pronounced differences in geometry renders a reliable assignment of the resonance lines to the individual sites on the basis of known empiric correlations and geometrical features impossible.