β-Xenophyllite-type Na4Li0.62Co5.67Al0.71(AsO4)6

The title compound, tetrasodium lithium cobalt aluminium hexa(orthoarsenate), was synthesized by a solid state reaction route. In the crystal structure, Co2+ ions are partially substituted by Al3+ in an octahedral environment [M1 with site symmetry 2/m; occupancy ratio Co:Al = 0.286 (10):0.714 (10)]. The charge compensation is ensured by Li+ cations sharing a tetrahedral site with Co2+ ions [M2 with site symmetry 2; occupancy ratio Co:Li = 0.690 (5):0.310 (5)]. The anionic unit is formed by two octahedra and three tetrahedra linked only by corners. The CoM1M2As2O19 units associate to an open three-dimensional framework containing tunnels propagating along the a-axis direction. One Na+ cation is located in the periphery of the tunnels while the other two are situated in the centres: all Na+ cations exhibit half-occupancy. The structure of the studied material is compared with those of various related minerals reported in the literature.