Search

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate dihydroxide, was synthesized under hydrothermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexagonal (001) 2∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octahedra and [AsO3.5(OH)0.5] tetrahedra 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-hexagonal 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. [ABSTRACT FROM AUTHOR]

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate dihydroxide, was synthesized under hydrothermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexagonal (001) 2∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]- layers formed from vertex- and edge-sharing [NiO4(OH)2] octahedra and [AsO3.5(OH)0.5] tetrahedra 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-hexagonal 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. [ABSTRACT FROM AUTHOR]

Single crystals of two basic cadmium phosphates, dicadmium orthophosphate hydroxide, Cd2(PO4)OH, and pentacadmium bis(orthophosphate) tetrakis(hydroxide), Cd5(PO4)2(OH)4, were obtained under hydrothermal 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 tetrahedral manner forming 18[(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 interactions 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] octahedra, and the other of two edge- and vertex-sharing [CdO6] octahedra. 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] tetrahedra. Quantitative structure comparisons are made with isotypic M5(XO4)2(OH)4 crystal structures (M = Cd, Mn, Co; X = P, As, V). [ABSTRACT FROM AUTHOR]

We introduce a strategy for the one‐step synthesis of chiral diazabicycloalkanes that delivers the annulated ring system in a single reaction step. The method entails a direct aza‐Michael/aldol reaction of enals in conjunction with modified oxopropanamides and establishes the chiral center via iminium‐enamine tandem catalysis. For this purpose, we developed simple diphenylethylendiamine frameworks as dual activation organocatalyst, effectively engaging both the substrate and reagent, thus leading to yields of 31–86% and enantioselectivities in the range of 80–98%. The final product features not only the diazabicycloalkane moiety but includes also additional functionalities, such as aldehyde motives that can be modified in situ without loss of enantioselectivity, and an sp2‐bearing methyl group. Our approach accommodates a wide array of enals with high functional group tolerance. Additionally, we demonstrated the adjustability of enantioselectivity and yield by modulating the acid cocatalyst's quantity, thus offering multiple optimization possibilities. [ABSTRACT FROM AUTHOR]

The re-investigation of [Bi2O2(OH)](NO3), dioxidodibismuth(III) hydroxide nitrate, on the basis of single-crystal X-ray diffraction data revealed an apparent structural phase transition of a crystal structure determined previously (space group Cmc21 at 173 K) to a crystal structure with lower symmetry (space group Pna21 at 100 K). The Cmc21 → Pna21 group–subgroup relationship between the two crystal structures is klassengleiche with index 2. In contrast to the crystal structure in Cmc21 with orientational disorder of the nitrate anion, disorder does not occur in the Pna21 structure. Apart from the disorder of the nitrate anion, the general structural set-up in the two crystal structures is very similar: [Bi2O2]2+ layers extend parallel to (001) and alternate with layers of (OH)− anions above and (NO3)− anions below the cationic layer. Whereas the (OH)− anion shows strong bonds to the BiIII cations, the (NO3)− anion weakly binds to the BiIII cations of the cationic layer. A rather weak O—HO hydrogen-bonding inter­action between the (OH)− anion and the (NO3)− anion links adjacent sheets along [001]. [ABSTRACT FROM AUTHOR]

In the context of investigating isostructural relationships between sulfates and monofluorophosphates, crystals of the double salts (NH4)2PO3F·NH4NO3 (AFP·AN) and (NH4)2XO4·3NH4NO3 (AX·3AN; X = Se, Cr) were grown from aqueous solutions and structurally characterized using X-ray diffraction and thermal analysis. Whereas the high-temperature forms of the two AX·3AN double salts are in fact isostructural with the sulfate analogue, AFP·AN crystallizes with a reduced amount of NH4NO3 and thus has a unique crystal structure. Both AFP·AN and the two AX·3AN compounds exhibit reversible structural phase transitions. Upon cooling, the monofluorophosphate double salt transforms from the monoclinic room-temperature polymorph (I; P21/n, Z = 4) to the intermediate triclinic polymorph (II; P1, Z = 4) that in turn transforms to the monoclinic low-temperature polymorph (III; P21/n, Z = 4). The two phase transitions (I) → (II) and (II) → (III) are characterized by a significant increase of the unit cell volumes upon cooling. The two AX·3AN double salts transform upon cooling from a disordered monoclinic crystal structure (P21, Z = 2) to a monoclinic polymorph with a doubled unit cell (P21/c, Z = 4). Such a phase transition is not observed for the sulfate analogue. All molecular moieties are fully ordered at −93 °C for the selenate double salt, whereas one of the nitrate anions remains disordered for the chromate double salt even at −173 °C. In all AFP·AN and AX·3AN crystal structures, the nitrate anions play a crucial role during the phase transitions, and an extensive network of N–H···O hydrogen-bonding interactions is responsible for the cohesion of the crystal. [ABSTRACT FROM AUTHOR]

During a systematic study on formation conditions of new compounds with zemannite-type structures, crystals of ten new oxidotellurate(IV) phases were grown under hydrothermal conditions, partially by employing a drastic reduction of the water content. The crystal structures of the obtained phases were determined by single-crystal X-ray diffraction. Na2[Ni2(TeO3)3]·2.5H2O, K2[Ni2(TeO3)3]·H2O, K2[Zn2(TeO3)3]·2H2O, Rb1.25[Co2(TeO3)3]·1.5H2O and Rb1.24[Mn2(TeO3)3]·2H2O exhibit a unit-cell with hexagonal symmetry (Z = 2, a ≈ 9.3 Å, c ≈ 7.7 Å), in which most of the other compounds with a zemannite-type structure are known to crystallize. Relative to this unit-cell, K2[Cu2(TeO3)3]·2H2O exhibits a twofold superstructure, K2[Co2(TeO3)3]·2.5H2O a twofold superstructure with an additional incommensurate modulation, Na2[Cu2(TeO3)3]·1.5H2O a threefold superstructure, and Rb1.5[Mn2(TeO3)3]·1.25H2O and Cs[Mn2(TeO3)3]·H2O a fourfold superstructure. Disorder of the alkali metal cations and crystal water molecules in the channels as well as variable water contents complicate modelling and structure refinement. [ABSTRACT FROM AUTHOR]