Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: Application to TeIVO6 octahedra

Christy, Andrew G. and Mills, Stuart J. (2013) Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: Application to TeIVO6 octahedra. Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 69 5: 446-456. doi:10.1107/S2052519213023087

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Author Christy, Andrew G.
Mills, Stuart J.
Title Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: Application to TeIVO6 octahedra
Formatted title
Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: Application to TeIVO6 octahedra
Journal name Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials   Check publisher's open access policy
ISSN 2052-5206
Publication date 2013-10-01
Sub-type Article (original research)
DOI 10.1107/S2052519213023087
Open Access Status File (Publisher version)
Volume 69
Issue 5
Start page 446
End page 456
Total pages 11
Place of publication Chichester, West Sussex, United Kingdom
Publisher Wiley-Blackwell Publishing
Language eng
Formatted abstract
The Distortion Theorem implies that the irregularity of bond distances in a distorted coordination polyhedron causes an increase of mean bond distance. Examination of 40 polyhedra containing the lone-pair cation TeIV shows that this does not imply an increase in polyhedral volume. Volumes of these polyhedra are 10.3-23.7-Å3, compared with the 12.83-Å3 expected for a hypothetical regular octahedron. There is little correlation between volume and measures of polyhedral distortion such as quadratic elongation, bond-angle variance or vector bond valence. However, the oxygens of our polyhedra lie very close to a sphere of best fit, centred at ∼-1-Å from the TeIV atom. The TeIV-centre distance is an index of lone-pair stereoactivity and is linearly related to the radius Rsph of the sphere; this is explained by a more localized lone pair repelling the anions more strongly, leading to a longer non-bonded distance between the lone pair and anions. Polyhedral volume still varies considerably for a given Rsph, because the oxygen ligands may be distributed over the whole sphere surface, or confined to a small portion of it. The uniformity of this distribution can be estimated from the distance between the sphere centre and the centroid of the O6 polyhedron. TeIV-centre and centroid-centre distances alone then account for 95% of the variation observed in volume for polyhedra which are topologically octahedral. Six of the polyhedra studied that are outliers are closer in shape to pentagonal pyramids than octahedra. These have short distances from the central TeIV cation to other TeIV and/or to large, polarizable cations, suggesting additional weak bonding interactions between these species and the central lone pair. The flexibility of lone-pair polyhedra is further enhanced by the ability of a single polyhedron to accommodate different cations with different degrees of lone-pair activity, which facilitates more diverse solid solution behaviour than would otherwise be the case.
Keyword Distortion theory
Lone-pair stereoactivity
Polyhedral distortion
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
 
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