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

La₃OClAsO₃]₂: A Lanthanum Oxide Chloride Oxoarsenate(III) with a “Lone‐Pair” Channel Structure La₃OClAsO₃]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 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.