La3OCl[AsO3](2): A lanthanum oxide chloride oxoarsenate(III) with a Lone-Pair channel structure

La3OCl[ASO(3)](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 degrees 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 [ASO(3)](3-) anions (d(As-O) = 175-179 pm) consist of three oxygen atoms (O2 and two O3), which surround the As cations together with the free, non-binding electron pair (lone pair) psi(1)-tetrahedrally (not less than(O-As-O) = 95 degrees, 3x). 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, 4x). These [(Ol)(La-2)(4)](10+) tetrahedra form endless infinity 1{[OLa4/2e](4+)} chains in the direction of the c axis through trans-edge condensation. Empty channels, constituted by the lonepair electrons of the Cl- anions and the As3+ cations in the psi(1)-tetrahedral oxoarsenate(III) anions [ASO(3)](3-), run parallel to [001] as well.