Physics and Chemistry of Minerals

, Volume 27, Issue 4, pp 270–284

Electron density distributions and bonded interactions for the fibrous zeolites natrolite, mesolite and scolecite and related materials

  • A. Kirfel
  • G. V. Gibbs
ORIGINAL PAPER

DOI: 10.1007/s002690050256

Cite this article as:
Kirfel, A. & Gibbs, G. Phys Chem Min (2000) 27: 270. doi:10.1007/s002690050256

Abstract

 For the fibrous zeolites natrolite, Na2[Al2Si3O10]·2H2O, mesolite, Na2Ca2[Al2Si3O10]3·8H2O, and scolecite, Ca[Al2Si3O10]·3H2O, with topologically identical aluminosilicate framework structures, accurate single-crystal X-ray diffraction data have been analyzed by least-squares refinements using generalized scattering factor (GSF) models. The final agreement indices were R(F ) = 0.0061, 0.0165, and 0.0073, respectively. Ensuing calculations of static deformation [Δρ(r)], and total, [ρ(r)], model electron density distributions served to study chemical bonding, in particular by topological electron density analyses yielding bond critical point (bcp) properties and in situ cation electronegativities. The results for 32 SiO, 24 AlO, 14 CaO, and 12 NaO unique bonds are compiled and analyzed in terms of both mean values and correlations between bond lengths, bonded oxygen radii, bcp densities, curvatures at the bcps, and electronegativities. Comparison with recent literature data obtained from both experimental electron density studies on minerals and model calculations for geometry-optimized molecules shows that the majority of the present findings conforms well with chemical expectation and with the trends observed from molecular modeling. For the SiO bond, the shared interaction is indicated to increase with decreasing bond length, whereas the AlO bond is of distinctly more polar nature, as is the NaO bond compared to CaO. Also, the observed ranges of the Si and Al in situ electronegativities and their mean electronegativities agree well with both Pauling's values and model calculation results, and statistically significant correlations are obtained which are consistent with trends described for oxide and nitride molecules.

Key words Electron density Topological analysis Zeolites 

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • A. Kirfel
    • 1
  • G. V. Gibbs
    • 2
  1. 1.Mineralogisch-Petrologisches Institut Poppelsdorfer Schloss, 53115 Bonn, Germany e-mail: kirfel@uni-bonn.de Fax: +49-228 73-2760DE
  2. 2.Department of Geological Sciences and Materials Sciences and Engineering and Mathematics, Virginia Tech, Blacksburg, Virginia 24061, USAUS