La3OCl[AsO3]2: Ein Lanthan‐Oxidchlorid‐Oxoarsenat(III) mit “lone‐pair”‐Kanalstruktur

Abstract

AbstractLa3OCl[AsO3]2: A Lanthanum Oxide Chloride Oxoarsenate(III) with a “Lone‐Pair” Channel StructureLa3OCl[AsO3]2 was prepared by the solid‐state reaction between La2O3 and As2O3 using LaCl3 and CsCl as fluxing agents in evacuated silica ampoules at 850 °C. The colourless crystals with pillar‐shaped habit crystallize tetragonally (a = 1299.96(9), c = 558.37(5) pm, c/a = 0.430) in the space group P42/mnm (no. 136) with four formula units per unit cell. The crystal structure contains two crystallographically different La3+ cations. (La1)3+ is coordinated by six oxygen atoms and two chloride anions in the shape of a bicapped trigonal prism (CN = 8), whereas (La2)3+ carries eight oxygen atoms and one Cl− anion arranged in the shape of tricapped trigonal prism (CN = 9). The isolated pyramidal [AsO3]3− anions (d(As–O) = 175–179 pm) consist of three oxygen atoms (O2 and two O3), which surround the As3+ cations together with the free, non‐binding electron pair (lone pair) Ψ1‐tetrahedrally (∢(O–As–O) = 95°, 3×). One of the three crystallographically independent oxygen atoms (O1), however, is exclusively coordinated by four (La2)3+ cations in the shape of a real tetrahedron (d(O–La) = 236 pm, 4×). These [(O1)(La2)4]10+ tetrahedra form endless $\rm ^{1}_{\infty}\{[OLa^{e}_{4/2}]^{4+}\}$ chains in the direction of the c axis through trans‐edge condensation. Empty channels, constituted by the lone‐pair electrons of the Cl− anions and the As3+ cations in the Ψ1‐tetrahedral oxoarsenate(III) anions [AsO3]3−, run parallel to [001] as well.