Abstract
Single crystals of two basic cadmium phosphates, dicadmium orthophosphate hydroxide, Cd(2)(PO(4))OH, and penta-cadmium bis-(orthophosphate) tetra-kis-(hydroxide), Cd(5)(PO(4))(2)(OH)(4), were obtained under hydro-thermal conditions. Cd(2)(PO(4))OH adopts the triplite [(Mn,Fe)(2)(PO(4))F] structure type. Its asymmetric unit comprises two Cd, one P and five O sites, all situated at the general Wyckoff position 8 f of space group I2/a; two of the O atoms are positionally disordered over two sites, and the H atom could not be localized. Disregarding the disorder, distorted [CdO(6)] polyhedra form a tri-periodic network by edge-sharing with neighbouring [CdO(6)] units and by vertex-sharing with [PO(4)] units. The site associated with the OH group is coordinated by four Cd atoms in a distorted tetra-hedral manner forming (1) (∞)[(OH)Cd(4/2)] 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(5)(PO(4))(2)(OH)(4) adopts the arsenoclasite [Mn(5)(AsO(4))(2)(OH)(4)] structure type. Its asymmetric unit comprises five Cd, two P, and twelve O sites all located at the general Wyckoff position 4 a of space group P2(1)2(1)2(1); the H atoms could not be localized. The crystal structure of Cd(5)(PO(4))(2)(OH)(4) can be subdivided into two main sub-units. One consists of three edge-sharing [CdO(6)] octa-hedra, and the other of two edge- and vertex-sharing [CdO(6)] 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(4)] tetra-hedra. Qu-anti-tative structure comparisons are made with isotypic M (5)(XO(4))(2)(OH)(4) crystal structures (M = Cd, Mn, Co; X = P, As, V).