Synthesis, crystal structure and magnetic properties of the open framework compound Co3Te2O2(PO4)2(OH)4

Cadmium phosphates Cd2(PO4)OH and Cd5(PO4)2(OH)4 crystallizing in mineral structures

Single crystals of two basic cadmium phosphates, dicadmium orthophosphate hydroxide, Cd2(PO4)OH, and penta-cadmium bis-(orthophosphate) tetra-kis-(hydroxide), Cd5(PO4)2(OH)4, were obtained under hydro-thermal conditions. Cd2(PO4)OH adopts the triplite [(Mn,Fe)2(PO4)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 [CdO6] polyhedra form a tri-periodic network by edge-sharing with neighbouring [CdO6] units and by vertex-sharing with [PO4] units. The site associated with the OH group is coordinated by four Cd atoms in a distorted tetra-hedral manner forming 1 ∞[(OH)Cd4/2] 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. Cd5(PO4)2(OH)4 adopts the arsenoclasite [Mn5(AsO4)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 P212121; the H atoms could not be localized. The crystal structure of Cd5(PO4)2(OH)4 can be subdivided into two main sub-units. One consists of three edge-sharing [CdO6] octa-hedra, and the other of two edge- and vertex-sharing [CdO6] 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 [PO4] tetra-hedra. Qu-anti-tative structure comparisons are made with isotypic M 5(XO4)2(OH)4 crystal structures (M = Cd, Mn, Co; X = P, As, V).

Ni3Te2O2(PO4)2(OH)4, an open-framework structure isotypic with Co3Te2O2(PO4)2(OH)4

Single crystals of Ni3(TeO(OH)2)2(PO4)2, trinickel(II) bis[(oxidodihydoxidotellurate(IV)] bis(phosphate),were obtained by hydro-thermal synthesis at 483 K, starting from NiCO3·2Ni(OH)2, TeO2 and H3PO4 in a molar ratio of 1:2:2. The crystal structure of Ni3Te2O2(PO4)2(OH)4 is isotypic with that of Co3Te2O2(PO4)2(OH)4 [Zimmermann et al. (2011 ▸). J. Solid State Chem. 184, 3080-3084]. The asymmetric unit comprises two Ni (site symmetries , 2/m) one Te (m), one P (m), five O (three m, two 1) and one H (1) sites. The tellurium(IV) atom shows a coordination number of five, with the corresponding [TeO3(OH)2] polyhedron having a distorted square-pyramidal shape. The two NiII atoms are both octa-hedrally coordinated but form different structural elements: one constitutes chains made up from edge-sharing [NiO6] octa-hedra extending parallel to [010], and the other isolated [NiO2(OH)4] octa-hedra. The two kinds of nickel/oxygen octa-hedra are connected by the [TeO3(OH)2] pyramids and the [PO4] tetra-hedra through edge- and corner-sharing into a three-dimensional framework structure with channels extending parallel to [010]. Hydrogen bonds of medium strength between the hy-droxy groups and one of the phosphate O atoms consolidate the packing. A qu-anti-tative structure comparison between Ni3Te2O2(PO4)2(OH)4 and Co3Te2O2(PO4)2(OH)4 is made.