Ilmenite-type Na2(Fe2/3Te4/3)O6.

Na2(Fe2/3Te4/3)O6 (Z = 3) or Na3(FeTe2)O9 (Z = 2), tris-odium iron(III) ditellurium(VI) nona-oxide, adopts the ilmenite (FeTiO3, Z = 6) structure type with the Ti site (site symmetry 3.) replaced by Na and the Fe site (site symmetry 3.) replaced by a mixed-occupied (FeIII,TeVI) site in a Fe:Te ratio of 1:2. Whereas the [(Fe,Te)O6] octa-hedron is only slightly distorted, the [NaO6] octa-hedron shows much stronger distortions, as revealed by a larger spread of the bond lengths and some distortion parameters.

Synthesis and crystal structure of (NH4)[Ni3(HAsO4)(AsO4)(OH)2].

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate di-hydroxide, was synthesized under hydro-thermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexa-gonal (001) 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octa-hedra and [AsO3.5(OH)0.5] tetra-hedra as the building units. The hydrogen atom of the OH group shows occupational disorder and was refined with a site occupation factor of 1/2, indicating the equal presence of [HAsO4]2- and [AsO4]3- groups. Strong asymmetric hydrogen bonds between symmetry-related (O,OH) groups of the arsenate units [O⋯O = 2.588 (18) Å] as well as hydrogen bonds accepted by these (O,OH) groups from OH groups bonded to the NiII atoms [O⋯O = 2.848 (12) Å] link adjacent layers. Additional consolidation of the packing is achieved through N-H⋯O hydrogen bonds from the ammonium ion, which is sandwiched between adjacent layers [N⋯O = 2.930 (7) Å] although the H atoms could not be located in the present study. The presence of the pseudo-hexa-gonal 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers may be the reason for the systematic threefold twinning of (NH4)[Ni3(HAsO4)(AsO4)(OH)2] crystals. Significant overlaps of the reflections of the respective twin domains complicated the structure solution and refinement.

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).

Crystal structure of K6[Zn(CO3)4].

The crystal structure of K6[Zn(CO3)4], hexa-potassium tetra-carbonato-zincate(II), comprises four unique potassium cations (two located on a general position, and two on the twofold rotation axis of the space group C2/c) and a [Zn(CO3)4]6- anion. The ZnII atom of the latter is located on the twofold rotation axis and is surrounded in a slightly distorted tetra-hedral manner by two pairs of monodentately binding carbonate groups, with Zn-O distances of 1.9554 (18) and 1.9839 (18) Å. Both carbonate groups exhibit a slight deviation from planarity, with the C atom being shifted by 0.008 (2) and 0.006 (3) Å, respectively, from the plane of the three O atoms. The coordination numbers of the potassium cations range from 6 to 8, using a threshold of 3.0 Šfor K-O bonding inter-actions being significant. In the crystal structure, [KOx] polyhedra and [Zn(CO3)4]6- groups share O atoms to build up the framework structure.

Garnet-type Na3Te2(FeO4)3.

Na3Te2(FeO4)3 or Na3Te2Fe3O12, tris-odium ditellurium(VI) triiron(III) dodeca-oxide, was obtained in the form of single-crystals under hydro-thermal conditions. Na3Te2(FeO4)3 adopts the garnet structure type in space group Ia d and comprises one Na (multiplicity 24, Wyckoff letter c, site symmetry 2.22), one Te (16 a, ..), one Fe (24 d, ..) and one O atom (96 h, 1) in the asymmetric unit. The three-dimensional framework structure is built of [TeO6] octa-hedra and [FeO4] tetra-hedra by vertex-sharing. The larger Na+ cations are situated in the inter-stices of the framework and are eightfold coordinated in the form of a distorted dodeca-hedron. Qu-anti-tative structural comparisons with isotypic Na3Te2[(Fe0.5Al0.5)O4]3 and Na3Te2(GaO4)3 show a high degree of similarity between the three crystal structures.

Crystal structure of Zn2(HTeO3)(AsO4).

Single crystals of Zn2(HTeO3)(AsO4), dizinc(II) hydroxidodioxidotellurate(IV) oxidoarsenate(V), were obtained as one of the by-products in a hydro-thermal reaction between Zn(NO3)2·6H2O, TeO2, H3AsO4 and NH3 in molar ratios of 2:1:2:10 at 483 K for seven days. The asymmetric unit of Zn2(HTeO3)(AsO4) contains one Te (site symmetry m), one As (m), one Zn (1), five O (three m, two 1) and one H (m) site. The ZnII atom exhibits a coordination number of 5 and is coordinated by four oxygen atoms and a hydroxide group, forming a distorted trigonal bipyramid. The hydroxide ion is positioned at a significantly larger distance on one of the axial positions of the bipyramid. The [ZnO4OH] polyhedra are connected to each other by corner-sharing to form ∞ 2[ZnO3/2(OH)1/2O1/1] layers extending parallel to (001). The TeIV atom is coordinated by three oxygen atoms and a hydroxide group in a one-sided manner in the shape of a bis-phenoid, revealing stereochemical activity of its 5s 2 electron lone pair. The AsV atom is coordinated by four oxygen atoms to form the tetra-hedral oxidoarsenate(V) anion. By corner-sharing, [TeO3OH] and [AsO4] groups link adjacent ∞ 2[ZnO3/2(OH)1/2O1/1] layers along [001] into a three-dimensional framework structure.

The crystal structure of a new CdTe2O5 polymorph, isotypic with ∊-CaTe2O5.

Single crystals of cadmium penta-oxidoditellurate(IV), CdTe2O5, were obtained as by-products in a hydro-thermal reaction of Cd(NO3)2·4H2O, TeO2, H6TeO6 and NH3 (molar ratios 2:1:1:6) at 483 K for seven days. The crystals represent a different polymorph (henceforth referred to as the ß-form) than the α-CdTe2O5 crystals grown from the melt, and are isotypic with hydro-thermally grown ∊-CaTe2O5. The asymmetric unit of ß-CdTe2O5 comprises one Cd, two Te and five O sites, all of which are located in general positions (Wyckoff position 4 e). The cadmium(II) atom is coordinated by seven oxygen atoms, forming 2 ∞[CdO6/2O1/1] (100) layers. Both tellurium sites are surrounded by four oxygen atoms with one of them being at a significantly longer distance than the other three. The resulting bis-phenoidal [TeO4] units also form layers propagating parallel to (100) by sharing edges with each other. The stereochemically active 5s 2 lone pair of the TeIV atoms leads to the formation of large channels extending along [011] and smaller ones along [010]. A qu-anti-tative comparison between the crystal structures of ß-CdTe2O5 and ∊-CaTe2O5 is made.

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.