ISSN:
1600-5740
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
In the present bond-valence concept the bond-valence parameter ro is treated as constant for a given pair of atoms, and it is assumed that the bond valence sij is a function of the corresponding bond length Dij, and that the atomic valence is an integer equal to the formal oxidation number forVi derived from stoichiometry. However, from a statistical analysis of 76 [SbIIISn] and 14 [SbIIISen] polyhedra in experimentally determined structures, it is shown that for SbIII—X bonds (X = S, Se), ro is correlated with {\bar \alpha}i, the average of the X—Sb—X angles between the three shortest Sb—X bonds. This is interpreted as a consequence of a progressive retraction of the 5s lone-electron pair from the SbIII nucleus, which can be considered as continuous change of the actual atomic valence actVi of Sb from +3 towards +5. A procedure is derived to calculate an effective atomic valence effVi of SbIII from the geometry, {\bar \alpha}i and Dij, of the [SbIIIXn] polyhedra, which approximates actVi and is a better description of the actual valence state of SbIII than the formal valence forVi. Calculated effVSbIII are found to vary between +2.88 and +3.80 v.u. for [SbIIISn] and between +2.98 and +3.88 v.u. for [SbIIISen] polyhedra. It is suggested that a corresponding modification of the present bond-valence concept is also required for other cations with lone-electron pairs.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0108768195004472
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