On oxytellurides (M2O2Te) of the early lanthanides (M = La-Nd, Sm-Ho) withA- or anti-ThCr2Si2-type crystal structure

By reacting elementary lanthanide metal (M = La-Nd, Sm-Ho) with tellurium d ioxide (TeO2) in a 2:1 molar ratio, it is possible to obtain pure and singl e-phase oxytellurides of the composition M2O2Te at 750 degrees C in evacuat ed silica tubes within a few days. When larger quantities of cesium chlorid e (CsCl) are added as flux, plate-like single crystals with square cross-se ction are formed which are not sensitive to hydrolysis and very suitable fo r crystal structure refinements from X-ray data. In the anri-ThCr2Si2 analo gous crystal structure (tetragonal, I4/mmm, Z = 2; La2O2Te: a = 412.31(4), c = 1309.6(1) pm; Ce2O2Te: a = 408.17(4), c = 1294.7(1) pm; Pr2O2Te: a = 40 5.62(4), c = 1285.8(1) pm: Nd2O2Te: a = 403.08(4), c = 1277.1(1) pm; Sm2O2T e: a = 399.83(4), c = 1265.5(1) pm; Eu2O2Te: a = 397.56(4), c = 1257.9(1) p m; Gd2O2Te: a = 396.20(4), c = 1253.2(1) pm; Tb2O2Te: a = 393.89(4), c = 12 45.4(1) pm; Dy2O2Te: a = 392.34(4), c = 1240.3(1)pm; Ho2O2Te: a = 390.57(6) , c = 1239.0(3) pm) the M3+ cations are surrounded by nine anions (4 O2- un d 4 + 1 Te2-) in the shape of a capped square antiprism. The anions show co ordination numbers of four (O2-: tetrahedra) and eight plus two (Te2-: bica pped cubes) with respect to the cations. PbO-analogous square (2)(infinity) ([OM4/4](2))(2+) triple layer slabs are present parallel (001), which origi nate through two-dimensional infinite linking of [OM4](10+) tetrahedra via two trans-orientated pairs of edges (i.e, four edges altogether). These cat ionic layers are piled alternatingly along [001] with likewise quadratic si ngle layers of Te2- anions, which take care of the three-dimensional cohere nce as well as of the charge balance.