Horst Schmidt

Crystal structures of hydrates of simple inorganic salts. I. Water‐rich magnesium halide hydrates MgCl2·8H2O, MgCl2·12H2O, MgBr2·6H2O, MgBr2·9H2O, MgI2·8H2O and MgI2·9H2O

The previously reported structures of the hydrates of simple inorganic salts that crystallize at room temperature are generally well determined. This is not true for water-rich hydrates, which crystallize at temperatures below 273 K. In this series, investigations of the crystal structures of water-rich hydrates crystallized from aqueous solutions at low temperatures are presented. Reported herein are the structures of a set of magnesium salts. Crystals of MgCl2·8H2O (magnesium dichloride octahydrate), MgCl2·12H2O (magnesium dichloride dodecahydrate), MgBr2·6H2O (magnesium dibromide hexahydrate), MgBr2·9H2O (magnesium dibromide nonahydrate), MgI2·8H2O (magnesium diiodide octahydrate) and MgI2·9H2O (magnesium diiodide nonahydrate) were grown from their aqueous solutions at temperatures below 298 K according to the solid-liquid phase diagrams. All structures are built up from Mg(H2O)6 octahedra. Dimensions and angles in the hexaaqua cation complexes are very similar and variation is not systematic. The anions are incorporated into a specific network of O-H...X hydrogen bonds.

Water channel structure of bassanite at high air humidity: crystal structure of CaSO4·0.625H2O.

Structure analysis using single-crystal diffraction was carried out as a contribution to the dispute about the nature of the water channel structure of bassanite (CaSO(4)·0.5H(2)O). A recent result of Weiss & Bräu (2009) for the crystal structure of bassanite (monoclinic, space group C2) at ambient conditions of air humidity was confirmed. In the presence of high relative air humidity the crystal structure of bassanite transformed due to the incorporation of additional water of hydration. The crystal structure of CaSO(4)·0.625H(2)O was solved by single-crystal diffraction at 298 K and 75% relative air humidity. The experimental results provided an insight into both crystal structures. A model explaining the phase transition from CaSO(4)·0.625H(2)O to CaSO(4)·0.5H(2)O was derived. The monoclinic cell setting of CaSO(4)·0.5H(2)O and the trigonal cell setting of CaSO(4)·0.625H(2)O were confirmed by powder diffraction.

CaSeO4-0.625H2O - Water Channel Occupation in a bassanite Related Structure

Calcium selenate subhydrate, CaSeO(4)·0.625H(2)O, was prepared by hydrothermal conversion of CaSeO(4)·2H(2)O at 463 K. From the single crystals obtained in the shape of hexagonal needles, 50-300 µm in length, the crystal structure could be solved in a trigonal unit cell with space group P3(2)21. The cell was confirmed and refined by high-resolution synchrotron powder diffraction. The subhydrate was characterized by thermal analysis and Raman spectroscopy.

Crystal structures of Sr(ClO4)2·3H2O, Sr(ClO4)2·4H2O and Sr(ClO4)2·9H2O

The crystal structures of the tri-, tetra- and nonahydrate phases of Sr(ClO4)2 consist of Sr2+ ions coordinated by nine oxygen atoms from water molecules and perchlorate tetrahedra. O—H⋯O hydrogen bonds between water molecules and ClO4 units lead to the formation of a three-dimensional network in each of the structures.

Magnesium chloride tetrahydrate, MgCl2·4H2O

The title compound, MgCl(2)·4H(2)O, was crystallized at 403 K and its structure determined at 200 K. The structure is built up from MgCl(2)(H(2)O)(4) octahedra with a trans configuration. Each complex is situated on a crystallographic twofold axis, with the rotation axis aligned along one H(2)O-Mg-OH(2) axis. They are connected by a complex network of O-H···Cl hydrogen bonds. The structure contains two-dimensional sections that are essentially identical to those in the reported tetrahydrates of CrCl(2), FeCl(2), FeBr(2) and CoBr(2), but they are stacked in a different manner in MgCl(2)·4H(2)O compared with the transition metal structures.

New iron(III) nitrate hydrates: Fe(NO3)3·xH2O with x = 4, 5 and 6

Crystals of the title compounds were grown from their hydrous melts or solutions. The crystal structure of iron(III) trinitrate hexahydrate {hexaaquairon(III) trinitrate, [Fe(H(2)O)(6)](NO(3))(3)} is built up from [Fe(H(2)O)(6)](2+) octahedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate pentahydrate {pentaaquanitratoiron(III) dinitrate, [Fe(NO(3))(H(2)O)(5)](NO(3))(2)}, one water molecule in the coordination octahedron of the Fe(III) atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetrahydrate {triaquadinitratoiron(III) nitrate monohydrate, [Fe(NO(3))(2)(H(2)O)(3)]NO(3)·H(2)O} represents the first example of a simple iron(III) nitrate with pentagonal-bipyramidal coordination geometry, where two bidentate nitrate anions and one water molecule form a pentagonal plane.

Crystal structures of Ca(ClO4)2·4H2O and Ca(ClO4)2·6H2O

The crystal structures of the tetra- and hexahydrate phases of Ca(ClO4)2 consist of Ca2+ ions in distorted square-antiprismatic environments and of perchlorate tetrahedra. O—H⋯O hydrogen bonds between water molecules and ClO4 units lead to the formation of a three-dimensional network in the structures.

Fe2(SO4)3·H2SO4·28H2O, a low-temperature water-rich iron(III) sulfate

The title compound, diiron(III) trisulfate-sulfuric acid-water (1/1/28), has been prepared at temperatures between 235 and 239 K from acid solutions of Fe2(SO4)3. Studies of the compound at 100 and 200 K are reported. The analysis reveals the structural features of an alum, (H5O2)Fe(SO4)2·12H2O. The Fe(H2O)6 unit is located on a centre of inversion at (½, 0, ½), while the H5O2(+) cation is located about an inversion centre at (½, ½, ½). The compound thus represents the first oxonium alum, although the unit cell is orthorhombic.

Lithium carnallite, LiCl.MgCl2.7H2O.

The title compound, lithium magnesium chloride heptahydrate, LiCl.MgCl(2).7H(2)O, was analyzed in 1988 by powder X-ray diffraction [Emons, Brand, Pohl & Köhnke (1988). Z. Anorg. Allg. Chem. 563, 180-184] and a monoclinic crystal lattice was determined. In the present work, the structure was solved from single-crystal diffraction data. A trigonal structure was found, exhibiting a network structure of Mg(H(2)O)(6) octahedra and Li(H(2)O)Cl(3) tetrahedra connected by H...Cl hydrogen bonds. The [Li(H(2)O)](+) unit is coordinated by distorted edge-connected Cl(-) octahedra.

Crystal structure of tin(II) perchlorate trihydrate

The title compound was synthesized by the redox reaction of copper(II) perchlorate hexahydrate and metallic tin in perchloric acid. Both the pyramidal [Sn(H2O)3]2+ cations and tetrahedral perchlorate anions lie on crystallographic threefold axes.