Non-centrosymmetric Ce3OCl[AsO3]2

The arsenite chloride Ce3OCl[AsO3]2 was synthesized in the form of colorless crystals from arsenic and cerium dioxide in a NaCl / KCl flux at 850 ◦C. Ce3OCl[AsO3]2 crystallizes with the noncentrosymmetric tetragonal Gd3OCl[AsO3]2 type, space group P42nm. The structure was refined from single crystal diffractometer data: a = 12.8590(6), c = 5.5627(3) Å, wR2 = 0.0429, 1463 F2 values, and 65 variables. The structure is built up from chains of trans edge-sharing OCe4/2 tetrahedra. The [AsO3]3− units coordinate to these chains via the oxygen atoms. Their lone-pairs point all to a common channel. Formation of the non-centrosymmetric superstructure is most likely driven by geometrical constraints and is discussed on the basis of a group-subgroup scheme.