Hostname: page-component-586b7cd67f-l7hp2 Total loading time: 0 Render date: 2024-11-28T04:09:14.288Z Has data issue: false hasContentIssue false

On the significance of small deviations from higher symmetry

Published online by Cambridge University Press:  05 July 2018

W. H. Baur*
Affiliation:
Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Avenue, Chicago, IL 60637, USA
R. X. Fischer
Affiliation:
Universität Bremen, Fachbereich Geowissenschaften, Kristallographie, Klagenfurter Strasse, D-28359 Bremen, Germany
*

Abstract

Small deviations from higher symmetry can be established by single-crystal diffraction methods by (1) measuring the metric of the unit cell with high, non-routine precision; (2) measuring a full reflection sphere of diffraction data and testing it for the presence or absence of symmetry elements in the dataset; (3) refining the structure in both the higher and the lower symmetry and comparing the results; (4) checking the refined crystal structures for the presence or absence of hidden symmetry elements. By these criteria it is not established that the v{120} growth sector of yugawaralite really has triclinic symmetry (Tanaka et al., 2002). On the contrary, the refined metrical parameters and the atomic positions conform to monoclinic symmetry within the margins of experimental error.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2003

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Baur, W.H. and Fischer, R.X. (2000 Zeolite-type crystal structures and their chemistry. Zeolite Structure Codes ABW to CZP, vol. B. ‘Microporous and other framework materials with zeolite-type structures’ (Baur, W.H. and Fischer, R.X., editors). Landolt-Börnstein, New Series IV/14, Springer, Berlin, 459 pp.Google Scholar
Baur, W.H. and Kassner, D. (1992 The perils of Cc: Comparing the frequencies of falsely assigned space groups with their general population. Acta Crystallographica , B48, 356369.CrossRefGoogle Scholar
Baur, W.H. and Ohta, T. (1981 Structure of magnesium disodium silicate Na2MgSiO4 and ionic conductivity in tetrahedral structures. Acta Crystallographica , B37, 14831491.CrossRefGoogle Scholar
Baur, W.H. and Tillmanns, E. (1986 How to avoid unnecessarily low symmetry in crystal structure determinations. Acta Crystallographica , B42, 95111.CrossRefGoogle Scholar
Baur, W.H., Joswig, W., Fursenko, B.A. and Belitsky, I.A. (1997 Symmetry reduction of the aluminosilicate framework of LAU topology by ordering of exchangeable cations: the crystal structure of primary leonhardite with a primitive Bravais lattice. European Journal of Mineralogy, 9, 11731182.CrossRefGoogle Scholar
Bond, W.L. (1960 Precision lattice constant determination. Acta Crystallographica, 13, 814818.CrossRefGoogle Scholar
Herbstein, F.H. (2000 How precise are measurements of unit-cell dimensions from single crystals? Acta Crystallographica , B56, 547557.CrossRefGoogle ScholarPubMed
Kahr, B. and McBride, J.M. (1992 Optically anomalous crystals. Angewandte Chemie International Edition, 31, 126.CrossRefGoogle Scholar
Le Page, Y. (1988 MISSYM 1.1 – a flexible new release. Journal of Applied Crystallography, 21, 983984.CrossRefGoogle Scholar
Marsh, R.E., Kapon, M., Hu, S. and Herbstein, F.H. (2002 Some 60 new space group corrections. Acta Crystallographica , B58, 6277.CrossRefGoogle ScholarPubMed
Sheldrick, G.M. (1993 SHELXL-93, a FORTRAN-77 program for the refinement of crystal structures from diffraction data . Universität Göttingen, Germany.Google Scholar
Stout, G.H. and Jensen, L.H. (1989 X-ray Structure Determination, a Practical Guide , 2nd edition. Wiley, New York, pp. 415420.Google Scholar
Tanaka, T., Kimura, R., Akizuki, M. and Kudoh, Y. (2002 Origin of low-symmetry growth vectors in edingtonite and yugawaralite, and crystal structure of the k﹛011﹜ and v﹛120﹜ sectors of yugawaralite. Mineralogical Magazine, 66, 409420.CrossRefGoogle Scholar
Taylor, R. and Kennard, O. (1986 Accuracy of crystal structure error estimates. Acta Crystallographica , B42, 112120.CrossRefGoogle Scholar
Tripathi, A., Parise, J.B., Kim, S.J., Lee, Y., Johnson, G.M. and Uh, Y.S. (2000 Structural changes and cation site ordering in Na and K forms of aluminogermanates with the zeolite gismondine topology. Chemistry of Materials, 12, 37603769.CrossRefGoogle Scholar