X‐ray and neutron powder diffraction analyses of Gly·MgSO 4 ·5H 2 O and Gly·MgSO 4 ·3H 2 O, and their deuterated counterparts

We have identified a new compound in the glycine–MgSO 4 –water ternary system, namely glycine magnesium sulfate trihydrate (or Gly·MgSO 4 ·3H 2 O) {systematic name: catena ‐poly[[tetraaquamagnesium(II)]‐μ‐glycine‐κ 2 O : O ′‐[diaquabis(sulfato‐κ O )magnesium(II)]‐μ‐glycine‐κ 2 O : O ′]; [Mg(SO 4 )(C 2 D 5 NO 2 )(D 2 O) 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·MgSO 4 ·5H 2 O) {systematic name: hexaaquamagnesium(II) tetraaquadiglycinemagnesium(II) disulfate; [Mg(D 2 O) 6 ][Mg(C 2 D 5 NO 2 ) 2 (D 2 O) 4 ](SO 4 ) 2 } above ∼330 K in air. X‐ray powder diffraction analysis reveals that the trihydrate phase is monoclinic (space group P 2 1 / n ), with a unit‐cell metric very similar to that of recently identified Gly·CoSO 4 ·3H 2 O [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( d 5 )·MgSO 4 ·5D 2 O] 2 , is triclinic (space group P , Z = 1), and glycine magnesium sulfate trihydrate, which may be described by the formula Gly( d 5 )·MgSO 4 ·3D 2 O, is monoclinic (space group P 2 1 / n , Z = 4). In the pentahydrate, there are two symmetry‐inequivalent MgO 6 octahedra on sites of symmetry and two SO 4 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, NH 3 + CH 2 COO − , adopts a monodentate coordination to Mg2. In the trihydrate, there are two pairs of symmetry‐inequivalent MgO 6 octahedra on sites of symmetry and two pairs of SO 4 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.