Zur Kenntnis eines Barium-Kupfer-Orthoarsenats: BaCu2(AsO4)2

On the Crystal Structure of Barium-Copper-Orthoarsenate BaCu₂(AsO₄)₂ Single crystals of BaCu₂(AsO₄)₂ were prepared above 1 000°C by CO₂-LASER technique and investigated by X-ray structure determination. The light blue crystals show monoclinic symmetry, space group C? P2₁/n, a = 4.752; b = 8.506; c = 8.945 Å; β = 93.49°, Z = 2. BaCu₂(AsO₄)₂ represents a hitherto unknown structure type with Cu²⁺ in trigonal bipyramidal coordination. Ba²⁺ shows an 8 + 2 surrounding by O^2? and As⁵⁺ is tetrahedrally coordinated. The crystal structure is discussed with respect to related orthophosphates and vanadates.