Structure of magnesium selenate enneahydrate, MgSeO4·9H2O, from 5 to 250 K using neutron time-of-flight Laue diffraction

Ba3[Sn(OH)6][SeO4]2·3H2O, a hydrated 1:2 double salt of barium hexahydroxidostannate(IV) and barium selenate(VI)

The title compound, Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O, was prepared by mimicking geochemical crystallization processes, and the hexa­gonal crystal structure determined. Its hierarchical structure comes from four different primary building units, setting up secondary building units that are arranged into layers via their {BaO₉} coordination polyhedra and cross-linked with the SBUs of adjacent layers via common [Sn(OH)₆]²⁻ ions.

Single crystals of tribarium hexa­hydroxidostannate(IV) bis­[selenate(VI)] trihydrate, Ba₃H₁₂O₁₇Se₂Sn or Ba₃[Sn(OH)₆][SeO₄]₂·3H₂O, prepared from solid BaSnO₃ and aqueous Na₂[SeO₄] solutions have hexa­gonal (P6₃) symmetry. The structure consists of four different primary building units: a hexa­hydroxidostannate(IV) ion, two different selenate(VI) ions, all three of point group symmetry C₃, and a mono-capped {BaO₉}-square anti­prism of point group symmetry C₁. The secondary building units result from three of the barium coordination polyhedra linked together via common edges. While one of the two tetra­hedral voids formed from these trimeric units is filled by one bidentate, chelating μ₂-selenate ion, the other one remains unoccupied as the corresponding second selenate ion only acts as a monodentate, μ₁-ligand. SBUs are completed by hexa­hydroxidostannate(IV) ions sharing adjacent edges on the uncapped faces of the three, mono-capped square anti­prisms. These SBUs are arranged into layers via common edges on the uncapped, square faces of the {BaO₉} coordination polyhedra in a way that the hexa­hydroxidostannate(IV) ions act as linkage between two neighboring layers.

Glycine zinc sulfate penta-hydrate: redetermination at 10 K from time-of-flight neutron Laue diffraction

Single crystals of glycine zinc sulfate penta-hydrate [systematic name: hexa-aqua-zinc tetra-aquadiglycinezinc bis-(sulfate)], [Zn(H2O)6][Zn(C2H5NO2)2(H2O)4](SO4)2, have been grown by isothermal evaporation from aqueous solution at room temperature and characterized by single-crystal neutron diffraction. The unit cell contains two unique ZnO6 octa-hedra on sites of symmetry -1 and two SO4 tetra-hedra with site symmetry 1; the octa-hedra comprise one [tetra-aqua-diglycine zinc]2+ ion (centred on one Zn atom) and one [hexa-aqua-zinc]2+ ion (centred on the other Zn atom); the glycine zwitterion, NH3+CH2COO-, adopts a monodentate coordination to the first Zn atom. All other atoms sit on general positions of site symmetry 1. Glycine forms centrosymmetric closed cyclic dimers due to N-H⋯O hydrogen bonds between the amine and carboxyl-ate groups of adjacent zwitterions and exhibits torsion angles varying from ideal planarity by no more than 1.2°, the smallest values for any known glycine zwitterion not otherwise constrained by a mirror plane. This work confirms the H-atom locations estimated in three earlier single-crystal X-ray diffraction studies with the addition of independently refined fractional coordinates and Uij parameters, which provide accurate inter-nuclear X-H (X = N, O) bond lengths and consequently a more accurate and precise depiction of the hydrogen-bond framework.

X-ray and neutron powder diffraction analyses of Gly·MgSO4·5H2O and Gly·MgSO4·3H2O, and their deuterated counterparts

We have identified a new compound in the glycine-MgSO4-water ternary system, namely glycine magnesium sulfate trihydrate (or Gly·MgSO4·3H2O) {systematic name: catena-poly[[tetraaquamagnesium(II)]-μ-glycine-κ(2)O:O'-[diaquabis(sulfato-κO)magnesium(II)]-μ-glycine-κ(2)O:O']; [Mg(SO4)(C2D5NO2)(D2O)3]n}, which can be grown from a supersaturated solution at ∼350 K and which may also be formed by heating the previously known glycine magnesium sulfate pentahydrate (or Gly·MgSO4·5H2O) {systematic name: hexaaquamagnesium(II) tetraaquadiglycinemagnesium(II) disulfate; [Mg(D2O)6][Mg(C2D5NO2)2(D2O)4](SO4)2} above ∼330 K in air. X-ray powder diffraction analysis reveals that the trihydrate phase is monoclinic (space group P21/n), with a unit-cell metric very similar to that of recently identified Gly·CoSO4·3H2O [Tepavitcharova et al. (2012). J. Mol. Struct. 1018, 113-121]. In order to obtain an accurate determination of all structural parameters, including the locations of H atoms, and to better understand the relationship between the pentahydrate and the trihydrate, neutron powder diffraction measurements of both (fully deuterated) phases were carried out at 10 K at the ISIS neutron spallation source, these being complemented with X-ray powder diffraction measurements and Raman spectroscopy. At 10 K, glycine magnesium sulfate pentahydrate, structurally described by the `double' formula [Gly(d5)·MgSO4·5D2O]2, is triclinic (space group P-1, Z = 1), and glycine magnesium sulfate trihydrate, which may be described by the formula Gly(d5)·MgSO4·3D2O, is monoclinic (space group P21/n, Z = 4). In the pentahydrate, there are two symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two SO4 tetrahedra with site symmetry 1. The octahedra comprise one [tetraaquadiglcyinemagnesium](2+) ion (centred on Mg1) and one [hexaaquamagnesium](2+) ion (centred on Mg2), and the glycine zwitterion, NH3(+)CH2COO(-), adopts a monodentate coordination to Mg2. In the trihydrate, there are two pairs of symmetry-inequivalent MgO6 octahedra on sites of -1 symmetry and two pairs of SO4 tetrahedra with site symmetry 1; the glycine zwitterion adopts a binuclear-bidentate bridging function between Mg1 and Mg2, whilst the Mg2 octahedra form a corner-sharing arrangement with the sulfate tetrahedra. These bridged polyhedra thus constitute infinite polymeric chains extending along the b axis of the crystal. A range of O-H...O, N-H...O and C-H...O hydrogen bonds, including some three-centred interactions, complete the three-dimensional framework of each crystal.