Use of differential calorimetry for characterization of hydration processes in the system Ca4(Al6O12) (SO4)-CaSO4.2H2O-H2O

Differential calorimetry was used to determine the heat evolution and kinetics of hydration processes of the calciumsulphatealuminate phase Ca₄(Al₆O₁₂)(SO₄) with gypsum CaSO₄ · 2H₂O at room temperature with one mole of water added to the solid phase. An increasing content of sulphate ions in the sytem results in substitution of the monosulphate Ca₄(Al₂O₆)(SO₄) · 12H₂O in the reaction products by ettringite, Ca₆(Al₂O₆)(SO₄)₃ · 32H₂O. Higher contents of ettringite influence the rates of hydration reactions and the values of the evolved heat.

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Zusammenfassung Die Wärmeentwicklung und ihr zeitlicher Ablauf bei der Hydratation des Calciumsulfat-aluminats Ca₄(Al₆O₁₂)SO₄ mit Gips CaSO₄ · 2H₂O bei Zimmertemperatur und einem Wasser/Feststoff-Massenverhältnisw/s=1 wurde durch isotherme Differenzkalorimetrie untersucht. Bei erhöhtem Sulfatgehalt wird das Monosulfat Ca₄(Al₂O₆)SO₄ · 12H₂O im Reaktionsprodukt durch Ettringit Ca₆(Al₂O₆)(SO₄)₃ · 32H₂O ersetzt. Der erhöhte Ettringitgehalt beeinflusst die Beschleunigung der Hydration und die abgegebene Wärmemenge.

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₃( l₆₁₂) (SO₄) . - ₆(l₂₆)(S₄)₃·32₂, .

     

Zur Kenntnis von Ag6(SO4)(SiO4)

About Ag₆(SO₄)(SiO₄) Hitherto unknown Ag₆(SO₄)(SiO₄) has been prepared at 400–500°C under an oxygen pressure more than 1000 atm. By single crystal X-ray work the structure of tetragonal Ag₆(SO₄)(SiO₄) has been elucidated: a = 7.060, c = 17.660 Å; D?14₁/amd; Z = 4. The crystal structure shows a new type in which the tetrahedrally sulfat- and silicat groups are definite distinguishable. As well the both crystallographic silver positions show a different crystal-chemical character.     

Structure determination and infrared spectroscopy of K(UO2)(SO4)(OH)(H2O) and K(UO2)(SO4)(OH)

Two potassium uranyl sulfate compounds were synthesized, and their crystal structures were determined by single-crystal X-ray diffraction. K(UO2)(SO4)(OH)(H2O) (KUS1) crystallizes in space group P21/c, a = 8.0521(4) A, b = 7.9354(4) A, c = 11.3177(6) A, beta = 107.6780(10) degrees , V = 689.01(6) A3, and Z = 4. K(UO2)(SO4)(OH) (KUS2) is orthorhombic Pbca, a = 8.4451(2) A, b = 10.8058(4) A, c = 13.5406(5)A, V = 1235.66(7)A3, and Z = 8. Both structures were refined on the basis of F2 for all unique data collected with Mo Kalpha radiation and a CCD-based detector to agreement indices R1 = 0.0251 and 0.0206 calculated for 2856 and 2616 reflections for KUS1 and KUS2, respectively. The structures contain vertex-sharing uranyl pentagonal bipyramids and sulfate tetrahedra linked into new chains and sheet topologies. Infrared spectroscopy provides additional information about the linkages between the sulfate and uranyl polyhedra, as well as the hydrogen bonding present in the structures. The U-O-S connectivity is examined in detail, and the local bond angle is impacted by the steric constraints of the crystal structure.     

Optical detection of spin polarization in single-molecule magnets [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(4)

A magneto-optical study has been undertaken of the mixed-valence single-molecule magnet [Mn(IV)(4)Mn(III)(8)O(12)L(16)] in which the ligands, L, are acetate (Mn(12)Ac) or the long-chain carboxylic acid, C(14)H(29)COOH (Mn(12)C(15)), that confers better solubility in organic solvents. Thin polymer films of these compounds in poly(methyl methacrylate) (PMM) have been cast by solvent evaporation to provide samples suitable for variable-temperature and field magnetic circular dichroism (MCD) studies. The absorption spectra in isotropic light are featureless, whereas the low-temperature MCD spectra contain resolved peaks, both positive and negative. MCD magnetization curves measured at temperatures above 4.2 K have established a ground-state spin of S = 10 and an axial zero-field parameter, D, of -0.61 K, similar to that determined for single crystals of Mn(12)Ac. By studying at a variety of optical wavelengths, the polarization ratios of the optical transitions relative to the unique axis of the zero-field distortion have been determined. The MCD magnetization curves measured at 4.2 K between 0 and 5 T for the case of Mn(12)C(15) in the PMM film can be fitted only on the assumption of nonrandom distribution of molecular z-axes arising from stresses in the polymer film during the process of casting. MCD-detected hysteresis curves measured in both frozen solution and PMM films, below the blocking temperature of approximately 3 K, show a high retention of spin polarization after reduction to zero of a polarizing magnetic field. This generates intense zero-field circular dichroism (CD) with maximum intensity for xy-polarized optical transitions whose sign depends on the direction of the original polarizing field. The optical polarization and the selection rules for MCD select a subset of molecular orientations with respect to the direction of field. Thus, the magnetically induced CD provides a highly sensitive and rapid optical method of reading the spin polarization of molecular magnets.     

Crystal structure of [Al4(OH)6(H2O)12][Al(H2O)6]2Br12: a new polyaluminum compound

A vertex-shared tetrahedral [Al(4)(OH)(6)(H(2)O)(12)](6+) (Al(4)) and a disordered [Al(H(2)O)(6)](3+) (Al(1)) that coexist in a 1:2 ratio within each unit cell were observed in the structure of [Al(4)(OH)(6)(H(2)O)(12)][Al(H(2)O)(6)](2)Br(12), which crystallized in a cubic Fd3m space group from a spontaneously hydrolyzed solution of AlBr(3). The former is composed of four AlO(6) octahedra that are connected to each other by sharing three vertexes of each octahedron and form a large regular tetrahedron with ideal T(d) symmetry. The central Al(3+) ion of the latter is coordinated by 6 disordered OH(2) molecules, that form a core-shell structure with ideal D(3d) symmetry.     

A Cationic Antimonite Chain Templated by Sulfate: [Sb(6)O(7)(4+)][(SO(4)(2-))(2)

An extended metal oxide possessing a cationic charge on the host has been synthesized by hydrothermal methods. The structure consists of 1D antimony oxide [Sb(6)O(7)](4+) chains with a new structural motif of four Sb atoms wide and unprotonated sulfate anions between the chains. The material was characterized by powder and single-crystal X-ray diffraction. Thermal behavior and chemical resistance in aqueous acidic conditions (pH ～2) indicate a highly stable cationic material. The stability is attributed to the entirely inorganic composition of the structure, where 1D covalently extended chains are electrostatically bound to divalent anions.     

Preparation and properties of the aqua ions [W(4)S(4)(H(2)O)(12)](n+) (n = 5, 6) and crystal structure of (Me(2)NH(2))(6)[W(4)S(4)(NCS)(12)].0.5H(2)O

The [3 + 1] reaction of [W(3)S(4)(H(2)O)(9)](4+) with [W(CO)(6)] in 2 M HCl under hydrothermal conditions (130 degrees C) gives the [W(4)S(4)(H(2)O)(12)](6+) cuboidal cluster, reduction potential 35 mV vs NHE (6+/5+ couple). The reduced form is obtained by controlled potential electrolysis. X-ray crystal structure was determined for (Me(2)NH(2))(6)[W(4)S(4)(NCS)(12)].0.5H(2)O. The W-W and W-S bond lengths are 2.840 and 2.379 A, respectively.     

Sequential hydration energies of the sulfate ion, from determinations of the equilibrium constants for the gas-phase reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O

Sequential hydration energies of SO4(H2O)(n)2- were obtained from determinations of the equilibrium constants of the following reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O. The SO4(2-) ions were produced by electrospray and the equilibrium constants Kn,n-1 were determined with a reaction chamber attached to a mass spectrometer. Determinations of Kn,n-1 at different temperatures were used to obtain DeltaG0n,n-1, DeltaH0 n,n-1, and DeltaS0n,n-1 for n = 7 to 19. Interference of the charge separation reaction SO4(H2O)(n)2- = HSO4(H2O)(n-k)- + OH(H2O)(k-1)- at higher temperatures prevented determinations for n < 7. The DeltaS0n,n-1 values obtained are unusually low and this indicates very loose, disordered structures for the n > or = 7 hydrates. The DeltaH0n,n-1 values are compared with theoretical values DeltaEn,n-1, obtained by Wang, Nicholas, and Wang. Rate constant determinations of the dissociation reactions n,n - 1, obtained with the BIRD method by Wong and Williams, showed relatively lower rates for n = 6 and 12, which indicate that these hydrates are more stable. No discontinuities of the DeltaG0n,n-1 values indicating an unusually stable n = 12 hydrate were observed in the present work. Rate constants evaluated from the DeltaG0n,n-1 results also fail to indicate a lower rate for n = 12. An analysis of the conditions used in the two types of experiments indicates that the different results reflect the different energy distributions expected at the dissociation threshold. Higher internal energies prevail in the equilibrium measurements and allow the participation of more disordered transition states in the reaction.     

Single-molecule magnets: a new family of Mn(12) clusters of formula [Mn(12)O(8)X(4)(O(2)CPh)(8)L(6)

The reaction of (NBu(n)(4))[Mn(8)O(6)Cl(6)(O(2)CPh)(7)(H(2)O)(2)] (1) with 2-(hydroxymethyl)pyridine (hmpH) or 2-(hydroxyethyl)pyridine (hepH) gives the Mn(II)(2)Mn(III)(10) title compounds [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hmp)(6)] (2) and [Mn(12)O(8)Cl(4)(O(2)CPh)(8)(hep)(6)] (3), respectively, with X = Cl. Subsequent reaction of 3 with HBr affords the Br(-) analogue [Mn(12)O(8)Br(4)(O(2)CPh)(8)(hep)(6)] (4). Complexes 2.2Et(2)O.4CH(2)Cl(2), 3.7CH(2)Cl(2), and 4.2Et(2)O.1.4CH(2)Cl(2) crystallize in the triclinic space group P1, monoclinic space group C2/c, and tetragonal space group I4(1)/a, respectively. Complexes 2 and 3 represent a new structural type, possessing isomeric [Mn(III)(10)Mn(II)(2)O(16)Cl(2)] cores but with differing peripheral ligation. Complex 4 is essentially isostructural with 3. A magnetochemical investigation of complex 2 reveals an S = 6 or 7 ground state and frequency-dependent out-of-phase signals in ac susceptibility studies that establish it as a new class of single-molecule magnet. These signals occur at temperatures higher than those observed for all previously reported single-molecule magnets that are not derived from [Mn(12)O(12)(O(2)CR)(16)(H(2)O)(x)]. A detailed investigation of forms of complex 2 with different solvation levels reveals that the magnetic properties of 2 are extremely sensitive to the latter, emphasizing the importance to the single-molecule magnet properties of interstitial solvent molecules in the samples. In contrast, complexes 3 and 4 are low-spin molecules with an S = 0 ground state.     

Cerium Complex with Four Types of Ligands: (NH4)6[Ce(H2W12O40)(C4H2O4)(NO3)(H2O)3]

A novel polymer (NH₄)₆[Ce(H₂W₁₂O₄₀)(C₄H₂O₄)(NO₃)(H₂O)₃] ( 1 ) has been constructed at room temperature and characterized by single crystal X‐ray structural analyses, elemental analyses, cyclic voltammetry, IR spectrum, and thermogravimetry. X‐ray structural analysis reveals that through the W–Ot′–Ce–Ob–W linkages a one‐dimension infinitely linear chain with alternating cations and anions is formed. 1 represents the first characterized compound that the Ce³⁺ ions are coordinated by four different types of ligands, and maleinate as ligands in constructing LnPOM architecture.     

Nanoscale Hemispheres in Novel Mixed-Valent Uranyl Chromate(V,VI), (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6)

The structure of a novel mixed-valent chromium uranyl compound, (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6) (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 ?(2) and a height of about 8 ?. The hemispheres are centered by a UO(8) hexagonal bipyramid surrounded by six dimers of Cr(5+)O(5) square pyramids, UO(7) pentagonal bipyramids, and Cr(6+)O(4) tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U(21)Cr(23) and can be considered as derivatives of nanospherical cluster U(26)Cr(36) composed of three-, four-, and five-membered rings.     

Crystal structure and spectroscopic properties of Na(2)K(6)(VO)(2)(SO(4))(7)

Red-brown crystals of a new mixed alkali oxo sulfato vanadium(V) compound Na(2)K(6)(VO)(2)(SO(4))(7), suitable for X-ray determination, have been obtained from the catalytically important binary molten salt system M(2)S(2)O(7)-V(2)O(5) (M = 80% K and 20% Na). By slow cooling of a mixture with the mole fraction X(V(2)O(5)) = 0.24 from 325 degrees C, i.e., just below the liquidus temperature, to the solidus temperature of around 300 degrees C, a dark reddish amorphous phase was obtained containing crystals of the earlier described V(V)-V(IV) mixed valence compound K(6)(VO)(4)(SO(4))(8) and Na(2)K(6)(VO)(2)(SO(4))(7) described here. This compound crystallizes in the tetragonal space group P4(3)2(1)2 (No. 96) with a = 9.540(3) A, c = 29.551(5) A at 20 degrees C and Z = 4. It contains a distorted VO(6) octahedron with a short V-O bond of 1.552(6) A, a long one of 2.276(5) A trans to this, and four equatorial V-O bonds in the range 1.881(6)-1.960(6) A. The deformation of the VO(6) octahedron is less pronounced compared to that of the known oxo sulfato V(V) compounds. Each VO(3+) group is coordinated to five sulfate groups of which two are unidentately coordinated and three are bidentate bridging to neighboring VO(3+) groups. The length of the S-O bonds in the S-O-V bridges of the two unidentately coordinated sulfato groups are 1.551(6) A and 1.568(6) A, respectively, which are unusually long compared to our earlier measurements of sulfate groups in other V(III), V(IV), and V(V) compounds.     

Crystal structure and luminescence of lanthanide monodentate complexes [Ln(C(4)N(4)H(6)O)(2)(H(2)O)(6)]Cl(3) and [Ln(C(4)N(4)H(6)O)(2)(H(2)O)(3)(NO(3))(3)] (Ln = Tb or Eu)

New eight- and nine-coordinate luminescent europium(III) and terbium(III) complexes 1-4 with carbonyl group coordination have been prepared using the monodentate ligand (L) 2,4-diamino-6-hydroxy pyrimidine and characterized by X-ray and spectroscopic methods.     

Layered Double Hydroxides Intercalated by Polyoxometalate Anions with Keggin (alpha-H(2)W(12)O(40)(6)(-)), Dawson (alpha-P(2)W(18)O(62)(6)(-)), and Finke (Co(4)(H(2)O)(2)(PW(9)O(34))(2)(10)(-)) Structures

The pillaring of Mg(3)Al layered double hydroxides (LDHs) by the title polyoxometalates (POMs) was accomplished by ion exchange reaction of the LDH-hydroxide and -adipate precursors with the POM anion at ambient or refluxing temperatures. The structural, thermal and textural properties of the LDH-POM intercalates were elucidated based on XRD, FTIR, TEM, EDS, and N(2) adsorption-desorption studies. A gallery height of approximately 10 ? was observed for the LDH intercalated by the symmetrical Keggin POM, whereas two different gallery heights were found for the cylindrical Dawson (14.5 and 12.8 ?) and Finke (13.3 and 12.6 ?) anions, depending on the preparation temperature. The differences in POM orientations were rationalized in terms of different electrostatic and hydrogen-bonding interactions between the POM pillars and the LDH layers. Upon thermal treatment at >/=100 degrees C, the intercalated Dawson and Finke POM ions exhibited only one gallery orientation, regardless of synthesis conditions. The crystalline microporous structures were retained upon heating each LDH-POM intercalate in N(2) to 200 degrees C. Pillaring in all cases was accompanied by the formation of a poorly ordered Mg(2+)/Al(3+) salt impurity that formed on the external surfaces of the LDH crystals.