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

Bond-valence parameters r 0 and b have been re-determined for Te IV-O: r 0 = 1.9605Ã…, b = 0.41; TeVI-O: r 0 = 1.921Ã…, b = 0.56; and TeIV-Cl: r 0 = 2.3115Ã…, b = 0.555. Bond distance data from 208 independent TeIV-O polyhedra, 118 Te VI-O polyhedra and 26 TeIV-Cl polyhedra were used, and all neighbours out to 3.5Ã… were included. Root-mean square deviations of bond-valence sums on Te from ideal values were 0.1934, 0.1939 and 0.0865v.u. The good fit for TeIV-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.