Crystal structure of magnesium copper(II) bis-[orthophosphate(V)] monohydrate

Single crystals of magnesium copper(II) bis-[orthophosphate(V)] monohydrate, Mg1.65Cu1.35(PO4)2·H2O, were grown under hydro-thermal conditions. The crystal structure is formed by three types of cationic sites and by two unique (PO4)(3-) anions. One site is occupied by Cu(2+), the second site by Mg(2+)and the third site by a mixture of the two cations with an Mg(2+):Cu(2+) occupancy ratio of 0.657 (3):0.343 (3). The structure is built up from more or less distorted [MgO6] and [(Mg/Cu)O5(H2O)] octa-hedra, [CuO5] square-pyramids and regular PO4 tetra-hedra, leading to a framework structure. Within this framework, two types of layers parallel to (-101) can be distinguished. The first layer is formed by [Cu2O8] dimers linked to PO4 tetra-hedra via common edges. The second, more corrugated layer results from the linkage between [(Cu/Mg)2O8(H2O)2] dimers and [MgO6] octa-hedra by common edges. The PO4 units link the two types of layers, leaving space for channels parallel [101], into which the H atoms of the water mol-ecules protrude. The latter are involved in O-H⋯O hydrogen-bonding inter-actions (one bifurcated) with framework O atoms across the channels.