Cadmium phosphates Cd(PO)OH and Cd(PO)(OH) crystallizing in mineral structures.

Single crystals of two basic cadmium phosphates, dicadmium orthophosphate hydroxide, Cd(PO)OH, and penta-cadmium bis-(orthophosphate) tetra-kis-(hydroxide), Cd(PO)(OH), were obtained under hydro-thermal conditions. Cd(PO)OH adopts the triplite [(Mn,Fe)(PO)F] structure type. Its asymmetric unit comprises two Cd, one P and five O sites, all situated at the general Wyckoff position 8 of space group 2/; two of the O atoms are positionally disordered over two sites, and the H atom could not be localized. Disregarding the disorder, distorted [CdO] polyhedra form a tri-periodic network by edge-sharing with neighbouring [CdO] units and by vertex-sharing with [PO] units. The site associated with the OH group is coordinated by four Cd atoms in a distorted tetra-hedral manner forming [(OH)Cd] chains parallel to [001]. The oxygen environment around the OH site suggests multiple acceptor atoms for possible O-H⋯O hydrogen-bonding inter-actions and is the putative reason for the disorder. Cd(PO)(OH) adopts the arsenoclasite [Mn(AsO)(OH)] structure type. Its asymmetric unit comprises five Cd, two P, and twelve O sites all located at the general Wyckoff position 4 of space group 222; the H atoms could not be localized. The crystal structure of Cd(PO)(OH) can be subdivided into two main sub-units. One consists of three edge-sharing [CdO] octa-hedra, and the other of two edge- and vertex-sharing [CdO] octa-hedra. Each sub-unit forms corrugated ribbons extending parallel to [100]. The two types of ribbons are linked into the tri-periodic arrangement through vertex-sharing and through common [PO] tetra-hedra. Qu-anti-tative structure comparisons are made with isotypic (O)(OH) crystal structures ( = Cd, Mn, Co; = P, As, V).