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  • 1
    Electronic Resource
    Electronic Resource
    Thermal Behaviour and Crystal Structure of Sodium-Containing Hemihydrates of Calcium Sulfate (1999)
    Springer
    Monatshefte für Chemie 130 (1999), S. 1179-1193 
    Details
    ISSN: 1434-4475
    Keywords: Keywords. Bassanite; Crystal structure; Sodium pentasalt; Calcium sulfate hemihydrate; Thermal analysis.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung.  Ein metastabiles natriumhaltiges Calciumsulfathemihydrat ((6−x) CaSO4ċxNa2SO4ċ3H2O, 0 ≤ x ≤ 1) tritt als intermediäre Phase in den Systemen Na2SO4-CaSO4-H2O, NaCl-Na2SO4-CaSO4-H2O und NaCl-CaSO4-H2O auf. Die Phase mit dem höchsten Natriumionengehalt entspricht dem sogenannten Natriumpentasalz (Na2SO4ċ5CaSO4ċ3H2O). Die Röntgenstrukturanalyse, welche an einem Einkristall mit Pentasalz-Zusammensetzung durchgeführt wurde, ergab eine Überstruktur des reinen Hemihydrats (CaSO4ċ0.5H2O), wobei ein Ca2+-Ion statistisch durch zwei Na+-Ionen ersetzt ist. Die Ca2+-Substitution erfolgt nur in einer der drei CaSO4-Ketten, welche eine nahezu dreizählige Achse entlang der c-Achse bilden. Ein Ca2+-Ion wird durch ein Na+-Ion ersetzt, das zweite Na+-Ion ist in unmittelbarer Nähe zum ersten in den Wasserkanälen eingelagert. Das Hydrat kristallisiert in der monoklinen Raumgruppe C121 (Nr.5) mit den Gitterparametern a=24.178(11), b=13.805(2), c=12.7074(12) Å, β=90.089(12)°. Die Dehydratationstemperatur variiert mit dem Na+-Gehalt. Je größer dieser ist, um so stärker wird der Austritt der H2O-Moleküle blockiert und zu höheren Temperaturen verschoben. Ein weiterer Unterschied im thermischen Verhalten wurde bei gleichem Na+-Gehalt für unterschiedliche Kristallitgrößen gefunden. Bei kleinen Kristallgrößen (Nadellänge 〈 20 μm) beginnt die Entwässerung früher im Vergleich zu größeren Kristallen (Nadellänge 〉 50 μm). Ein exothermer Effekt im Anschluß an die Dehydratation wird nur für kleine Kristalle beobachtet und deutet auf eine abweichende Entwässerungskinetik in Abhänigkeit von der Kristallitgröße hin.
    Notes: Summary.  A metastable sodium-containing hemihydrate ((6-x)CaSO4ċxNa2SO4ċ3H2O, 0 ≤ x ≤ 1) limited by the pentasalt composition Na2SO4ċ5CaSO4ċ3H2O occurs as an intermediate solid phase in the systems Na2SO4-CaSO4-H2O, NaCl-Na2SO4-CaSO4-H2O, and NaCl-CaSO4-H2O. X-Ray structure determination of a crystal with pentasalt composition results in a super-structure of the pure hemihydrate (CaSO4ċ0.5H2O), in which one Ca2+ion is statistically replaced by two Na+ ions. One Na+ cation is situated in a Ca2+ position in only one of the three chains of CaSO4 forming an axis of nearly three fold symmetry along the c-axis. The second Na+ is located in the water channel neighbouring to the first Na+. The hydrate crystallized in a monoclinic space group C121 (No. 5) with a=24.1781(11), b=13.805(2), c=12.7074(12) Å, β=90.089(12)°. The dehydration temperature of the hydrates depends on their Na+ ion content. A high Na+ content (in water channels) blocks the water escape strongly, and the dehydration temperature increases. Thermal behaviour is also effected by the crystal sizes. The thermograms of small crystals as opposed to large ones show a exothermic effect adjoining the endothermic dehydration. This may be indicative for a change in the dehydration mechanism upon crystal size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010180
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  • 2
    Electronic Resource
    Electronic Resource
    Crystallization Sequence of Brines–Geometrical Principles for a Computer Assisted Calculation (2000)
    Springer
    Monatshefte für Chemie 131 (2000), S. 25-37 
    Details
    ISSN: 1434-4475
    Keywords: Keywords. Sea water; Brine; Crystallization sequence; Simulation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung.  Die Kristallisationsabfolge beim Abdampfen von Salzsolen wurde bei 25°C aufder Basis der entsprechenden Phasendiagramme computerunterstützt berechnet. Dabei wurden sowohl die auskristallisierenden festen Phasen bestimmt als auch deren Massenbilanzen ermittelt. Um quantitative Information über das Abdampfverhalten von Salzsolen zu erhalten, wurden diesen Berechnungen zwei Grenzannahmen zugrunde gelegt: i) das Fest-flüssig-Gleichgewicht stellt sich laufend ein, sodaß sich feste Phasen während des Verdampfungsprozesses teilweise oder vollständig wieder auflösen können, bzw. ii) die festen Phasen sedimentieren und trennen sich von der flüssigen Phase, sodaß keine Wiederauflösung möglich ist. Tages- bzw. jahreszeitliche Temperaturschwankungen sowie metastabile Gleichgewichte wurden nicht berücksichtigt.
    Notes: Summary.  A computer assisted calculation of the crystallization sequence of a brine is performed on the basis of the respective phase diagrams at 25°C. The nature of the solids and the mass balance are determined. The calculation gives immediate quantitative information of the brine behavior during evaporation. The calculation is performed assuming that i) the solids are always in equilibrium with the liquid, i.e. that some solid phases can be partially or completely redissolved during evaporation, or ii) the solids are separated from liquid by sedimentation and no redissolution is possible. The seasonal or day-night fluctuations of temperature and metastable equilibria have not been taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00010297
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  • 3
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    Crystal structure and characterization of magnesium carbonate chloride heptahydrate (2020)
    International Union of Crystallography
    Details
    Publication Date: 2020-07-08
    Description: MgCO3·MgCl2·7H2O is the only known neutral magnesium carbonate containing chloride ions at ambient conditions. According to the literature, only small and twinned crystals of this double salt could be synthesised in a concentrated solution of MgCl2. For the crystal structure solution, single-crystal diffraction was carried out at a synchrotron radiation source. The monoclinic crystal structure (space group Cc) exhibits double chains of MgO octahedra linked by corners, connected by carbonate units and water molecules. The chloride ions are positioned between these double chains parallel to the (100) plane. Dry MgCO3·MgCl2·7H2O decomposes in the air to chlorartinite, Mg2(OH)Cl(CO3)·nH2O (n = 2 or 3). This work includes an extensive characterization of the title compound by powder X-ray diffraction, thermal analysis, SEM and vibrational spectroscopy.
    Electronic ISSN: 2053-2296
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 4
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    Crystallization of metastable monoclinic carnallite, KCl·MgCl2·6H2O: missing structural link in the carnallite family (2020)
    International Union of Crystallography
    Details
    Publication Date: 2020-04-29
    Description: During evaporation of natural and synthetic K–Mg–Cl brines, the formation of almost square plate-like crystals of potassium carnallite (potassium chloride magnesium dichloride hexahydrate) was observed. A single-crystal structure analysis revealed a monoclinic cell [a = 9.251 (2), b = 9.516 (2), c = 13.217 (4) Å, β = 90.06 (2)° and space group C2/c]. The structure is isomorphous with other carnallite-type compounds, such as NH4Cl·MgCl2·6H2O. Until now, natural and synthetic carnallite, KCl·MgCl2·6H2O, was only known in its orthorhombic form [a = 16.0780 (3), b = 22.3850 (5), c = 9.5422 (2) Å and space group Pnna].
    Electronic ISSN: 2053-2296
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 5
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    Water channel structure of bassanite at high air humidity: crystal structure of CaSO4·0.625H2O (2011)
    International Union of Crystallography
    Details
    Publication Date: 2011-11-17
    Description: 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 (CaSO4·0.5H2O). A recent result of Weiss & Bräu (2009) for the crystal structure of bassanite (monoclinic, space groupC2) 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 CaSO4·0.625H2O 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 CaSO4·0.625H2O to CaSO4·0.5H2O was derived. The monoclinic cell setting of CaSO4·0.5H2O and the trigonal cell setting of CaSO4·0.625H2O were confirmed by powder diffraction.
    Print ISSN: 0108-7681
    Electronic ISSN: 1600-5740
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by International Union of Crystallography
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  • 6
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    Crystal structure of tin(IV) chloride octahydrate (2014)
    International Union of Crystallography
    Details
    Publication Date: 2014-11-12
    Description: The title compound, [SnCl4(H2O)2]·6H2O, was crystallized according to the solid–liquid phase diagram at lower temperatures. It is built-up of SnCl4(H2O)2octahedral units (point group symmetry 2) and lattice water molecules. An intricate three-dimensional network of O—H...O and O—H...Cl hydrogen bonds between the complex molecules and the lattice water molecules is formed in the crystal structure.
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
    Published by International Union of Crystallography
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  • 7
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    Crystal structures of Ca(ClO4)2·4H2O and Ca(ClO4)2·6H2O (2014)
    International Union of Crystallography
    Details
    Publication Date: 2014-11-15
    Description: The title compounds, calcium perchlorate tetrahydrate and calcium perchlorate hexahydrate, were crystallized at low temperatures according to the solid–liquid phase diagram. The structure of the tetrahydrate consists of one Ca2+cation eightfold coordinated in a square-antiprismatic fashion by four water molecules and four O atoms of four perchlorate tetrahedra, forming chains parallel to [01-1] by sharing corners of the ClO4tetrahedra. The structure of the hexahydrate contains two different Ca2+cations, each coordinated by six water molecules and two O atoms of two perchlorate tetrahedra, forming [Ca(H2O)6(ClO4)]2dimers by sharing two ClO4tetrahedra. The dimers are arranged in sheets parallel (001) and alternate with layers of non-coordinating ClO4tetrahedra. O—H...O hydrogen bonds between the water molecules as donor and ClO4tetrahedra and water molecules as acceptor groups lead to the formation of a three-dimensional network in the two structures. Ca(ClO4)2·6H2O was refined as a two-component inversion twin, with an approximate twin component ratio of 1:1 in each of the two structures.
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
    Published by International Union of Crystallography
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  • 8
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    Crystal structure of iron(III) perchlorate nonahydrate (2014)
    International Union of Crystallography
    Details
    Publication Date: 2014-11-12
    Description: Since the discovery of perchlorate salts on Mars and the known occurrence of ferric salts in the regolith, there is a distinct possibility that the title compound could form on the surface of Mars. [Fe(H2O)6](ClO4)3·3H2O was crystallized from aqueous solutions at low temperatures according to the solid–liquid phase diagram. It consists of Fe(H2O)6octahedra (point group symmetry -3.) and perchlorate anions (point group symmetry .2) as well as non-coordinating water molecules, as part of a second hydrogen-bonded coordination sphere around the cation. The perchlorate appears to be slightly disordered, with major–minor component occupancies of 0.773 (9):0.227 (9).
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
    Published by International Union of Crystallography
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  • 9
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    Crystal structures of ZnCl2·2.5H2O, ZnCl2·3H2O and ZnCl2·4.5H2O (2014)
    International Union of Crystallography
    Details
    Publication Date: 2014-11-15
    Description: The formation of different complexes in aqueous solutions is an important step in understanding the behavior of zinc chloride in water. The structure of concentrated ZnCl2solutions is governed by coordination competition of Cl−and H2O around Zn2+. According to the solid–liquid phase diagram, the title compounds were crystallized below room temperature. The structure of ZnCl2·2.5H2O contains Zn2+both in a tetrahedral coordination with Cl−and in an octahedral environment defined by five water molecules and one Cl−shared with the [ZnCl4]2−unit. Thus, these two different types of Zn2+cations form isolated units with composition [Zn2Cl4(H2O)5] (pentaaqua-μ-chlorido-trichloridodizinc). The trihydrate {hexaaquazinc tetrachloridozinc, [Zn(H2O)6][ZnCl4]}, consists of three different Zn2+cations, one of which is tetrahedrally coordinated by four Cl−anions. The two other Zn2+cations are each located on an inversion centre and are octahedrally surrounded by water molecules. The [ZnCl4] tetrahedra and [Zn(H2O)6] octahedra are arranged in alternating rows parallel to [001]. The structure of the 4.5-hydrate {hexaaquazinc tetrachloridozinc trihydrate, [Zn(H2O)6][ZnCl4]·3H2O}, consists of isolated octahedral [Zn(H2O)6] and tetrahedral [ZnCl4] units, as well as additional lattice water molecules. O—H...O hydrogen bonds between the water molecules as donor and ZnCl4tetrahedra and water molecules as acceptor groups leads to the formation of a three-dimensional network in each of the three structures.
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
    Published by International Union of Crystallography
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  • 10
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    Crystal structures of Sr(ClO4)2·3H2O, Sr(ClO4)2·4H2O and Sr(ClO4)2·9H2O (2014)
    International Union of Crystallography
    Details
    Publication Date: 2014-11-15
    Description: The title compounds, strontium perchlorate trihydrate {di-μ-aqua-aquadi-μ-perchlorato-strontium, [Sr(ClO4)2(H2O)3]n}, strontium perchlorate tetrahydrate {di-μ-aqua-bis(triaquadiperchloratostrontium), [Sr2(ClO4)4(H2O)8]} and strontium perchlorate nonahydrate {heptaaquadiperchloratostrontium dihydrate, [Sr(ClO4)2(H2O)7]·2H2O}, were crystallized at low temperatures according to the solid–liquid phase diagram. The structures of the tri- and tetrahydrate consist of Sr2+cations coordinated by five water molecules and four O atoms of four perchlorate tetrahedra in a distorted tricapped trigonal–prismatic coordination mode. The asymmetric unit of the trihydrate contains two formula units. Two [SrO9] polyhedra in the trihydrate are connected by sharing water molecules and thus forming chains parallel to [100]. In the tetrahydrate, dimers of two [SrO9] polyhedra connected by two sharing water molecules are formed. The structure of the nonahydrate contains one Sr2+cation coordinated by seven water molecules and by two O atoms of two perchlorate tetrahedra (point group symmetry ..m), forming a tricapped trigonal prism (point group symmetrym2m). The structure contains additional non-coordinating water molecules, which are located on twofold rotation axes. O—H...O hydrogen bonds between the water molecules as donor and ClO4tetrahedra and water molecules as acceptor groups lead to the formation of a three-dimensional network in each of the three structures.
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
    Published by International Union of Crystallography
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