Abstract
Bond valence parameters r
~0~ and b have been re-determined for ^[3–11]^Sb(III)–O and ^[6]^Sb(V)–O, utilising crystal structures of natural and inorganic compounds from the Inorganic Crystal Structure Database. Bond valence parameters for Sb(III) were obtained from a best-fit r
~0~–b curve for 242 independent SbO~n~ polyhedra. For ^[6]^Sb(V), a curve of best fitting r
~0~–b pairs was determined by fitting to 207 independent SbO~6~ octahedra; b was then determined by optimising bond valence sums on the oxygens of Sb~2~O~5~ and Sb~2~O~4~, given the limited low quality structural data available for Sb(V) coordination numbers other than 6. Parameter values that minimised r.m.s. deviation from the ideal bond valence sums were r
~0~ = 1.925 Å and b = 0.455 Å for Sb(III) and r
~0~ = 1.904 Å, b = 0.430 Å for ^[6]^Sb(V). The increase in r
~0~ for Sb(III) may represent the repulsive effect of the lone-pair electrons, while the difference in b indicates higher polarisability when these electrons are present. Consideration of subsets of data for differing coordination numbers demonstrates that Sb(III) parameters are applicable to all SbO~n~ coordination numbers (CN = 3–11). We also show that the apparent overbonding using the classical b value cannot be an artefact of unresolved site splitting. For Sb(V), independent determination of b allows bond lengths cautiously to be estimated for CN ≠ 6. This work confirms that the “universal” value b = 0.37 Å is not adequate for heavier cations such as Sb.