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)]-[mu]-glycine-[kappa]2O:O'-[diaquabis(sulfato-[kappa]O)mag­nes­ium(II)]-[mu]-glycine-[kappa]2O: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\overline{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 \overline 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 \overline 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