Revised values of the bond-valence parameters for Te^IV-O, Te^VI-O and Te^IV-Cl

Bond-valence parameters r₀ and b have been re-determined for Te^IV-O: r₀ = 1.9605 Å, b = 0.41; Te^VI-O: r₀ = 1.921 Å, b = 0.56; and Te^IV-Cl: r₀ = 2.3115 Å, b = 0.555. Bond distance data from 208 independent Te^IV-O polyhedra, 118 Te^VI-O polyhedra and 26 Te^IV-Cl polyhedra were used, and all neighbours out to 3.5 Å were included. Root-mean square deviations of bond-valence sums on Te from ideal values were 0.1934, 0.1939 and 0.0865 v.u. The good fit for Te^IV-O over a range of Te coordination numbers from 3 to 12 demonstrates that there is no essential difference in character between short `primary' Te-O bonds, oriented away from the Te lone pair, and longer `secondary' Te-O bonds on the same side of the Te atom as the lone pair. Comparison of bond-valence sums for Te-O polyhedra obtained using the new parameters with those calculated using earlier literature values shows that the new parameters give a narrower spread of calculated bond-valence sums, which means much closer to the formal valence for both oxidation states of tellurium.