Ein neues Selten-Erd-Metall(III)-Oxidchlorid-Oxotellurat(IV): Nd5O4Cl3[TeO3]2 A New Rare Earth-Metal(III) Oxide Chloride Oxotellurate(IV): Nd5O4Cl3[TeO3]2

Pale violet, plate-like single crystals of the title compound, neodymium(III) oxide chloride oxotellurate(IV) Nd5O4Cl3[TeO3]2, can be obtained by the reaction of Nd2O3 with NdCl3 and TeO2 in equimolar ratios in evacuated silica ampoules within five days at 775 ◦Cwith an excess of CsCl added as fluxing agent. Nd5O4Cl3[TeO3]2 crystallizes in the monoclinic space group C2/m (no. 12) with the lattice parameters a = 1270.61(9), b = 562.70(4), c = 1008.97(8) pm, β = 90.784(3)◦ and Z = 2, and is thus isostructural to the lanthanoid(III) oxide halide oxoselenates(IV) Tb5O4Cl3[SeO3]2 and Gd5O4Br3[SeO3]2. The crystal structure exhibits three crystallographically different Nd3+ cations, of which (Nd1)3+ has a purely oxidic coordination sphere of eight oxide anions building up a square prism. (Nd2)3+ and (Nd3)3+ are both coordinated by oxide and chloride anions. The coordination polyhedron around (Nd2)3+ is a trigonal prism of oxide anions that is capped by one chloride anion to give a coordination number of seven. (Nd3)3+ resides in an eightfold coordination of five oxide and three chloride anions forming a square antiprism. All (O1)2− anions are surrounded tetrahedrally by Nd3+ cations as [ONd4] units. These tetrahedra share common edges and vertices to generate two-dimensional infinite layers of the composition ∞{[O4Nd5]}, which extend parallel to the (001) plane. The chloride anions (Cl1)− are connecting those slabs via Nd3–Cl1–Nd3 bridges along the [001] direction, while the (Cl2)− anions alternate with the Te4+ cations above and below the layers. The three-dimensional crystal structure of Nd5O4Cl3[TeO3]2 is completed by Te4+ cations, which are bonded to one (O2)2− and two (O3)2− anions to form ψ1-tetrahedra [TeO3]2− with a nonbinding, stereochemically active electron pair (“lone pair”) pointing into the free space between the chloride-decorated ∞{[O4Nd5]} layers.