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Apatite-type silicates Y7.75Dy0.25Ca2(SiO4)6O2 and Dy8Ca2(SiO4)6O2 were prepared by high-temperature solid state synthesis. In the crystal lattice, Dy3+ partially substitutes Ca2+, preferably at the 6h Ca2-site, and forms a short bond of 2.2 Å with the intra-channel O2−. The imposed strong ligand field anisotropy provides large magnetic anisotropy, which manifests itself as slow relaxation of magnetization at low temperatures. The magnetic dynamics is characterized by three or two characteristic values of relaxation time, respectively, which may be attributed to a single Dy3+ center. A phenomenological model is proposed which explains this response in terms of single paramagnetic center multiple relaxation. [ABSTRACT FROM AUTHOR]

Ferrous glycine sulfate pentahydrate [Fe(glycine)(SO4)·5H2O with glycine = C2H5NO2], contained in the supplement for treating iron deficiency anaemia, commercially known as ferro sanol duodenal®, was characterized by laboratory X‐ray powder diffraction (XRPD), scanning electron microscope (SEM), and infrared spectroscopy (IR). The thermal behavior was investigated by thermal analysis (TGA and DTA) and temperature‐dependent in situ XRPD measurements. Furthermore, the phase transitions to a less hydrated form [Fe(glycine)(SO4)·3H2O] and successively to the anhydrous form were demonstrated to occur in the crystalline solid state. Compared to the crystal structure of the pentahydrate, the trihydrate exhibits a different coordination environment of the iron sites where glycine ligands bridge iron forming a 1D polymeric chain structure. From detailed structural comparison, the mechanism of the phase transitions can be concluded. [ABSTRACT FROM AUTHOR]

In the course of solid-state photoreactions, a single crystal (SC) of the reactant can be transformed into an SC of the product or it can lose crystallinity and become amorphous. In-between these two scenarios exist the reconstructive phase transformations, where upon irradiation, the reactant SC becomes a powder or an SC with increased mosaicity. We present a detailed description of reconstructive photodimerization, where the structural changes are directly correlated with the disintegration process. The kinetics of the reaction is explained by two kinetic regimes, forming an autocatalytic autoinhibition photoreaction set with high quantum yield. In addition, the photoreaction pathways were studied theoretically. [ABSTRACT FROM AUTHOR]

The application of rotational symmetry modes to quantitative rigid-body analysis is demonstrated for octahedral rotations in Mg(H2O)6RbBr3. Rigidbody rotations are treated as axial-vector order parameters and projected using group-theoretical methods. The high-temperature crystal structure of the Mg(H2O)6RbBr3 double salt consists of a cubic perovskite-like corner-sharing network of RbBr6 octahedra with isolated MgO6 octahedra at the perovskite A sites. A phase transition occurs at 411 K upon cooling, whereupon the MgO6 octahedra experience a substantial rigid-body rotation, the RbBr6 octahedra are translated but not rotated, and both types of octahedra become slightly distorted. The MgO6 rotation has three orthogonal components associated with the X-5, Γ4 + and X1 - irreducible representations of the parent Pm3m space-group symmetry which, given the weakly first-order character of the transition, appear to be strongly coupled. Parametric and sequential refinements of the temperature-dependent structure were conducted using four model types: (1) traditional atomic xyz coordinates for each atom, (2) traditional rigid-body parameters, (3) purely displacive symmetry modes and (4) rigid-body rotational symmetry modes. We demonstrate that rigid-body rotational symmetry modes are an especially effective parameter set for the Rietveld characterization of phase transitions involving polyhedral rotations. [ABSTRACT FROM AUTHOR]

The application of rotational symmetry modes to quantitative rigid-body analysis is demonstrated for octahedral rotations in Mg(H2O)6RbBr3. Rigidbody rotations are treated as axial-vector order parameters and projected using group-theoretical methods. The high-temperature crystal structure of the Mg(H2O)6RbBr3 double salt consists of a cubic perovskite-like corner-sharing network of RbBr6 octahedra with isolated MgO6 octahedra at the perovskite A sites. A phase transition occurs at 411 K upon cooling, whereupon the MgO6 octahedra experience a substantial rigid-body rotation, the RbBr6 octahedra are translated but not rotated, and both types of octahedra become slightly distorted. The MgO6 rotation has three orthogonal components associated with the X-5, Γ4 + and X1 - irreducible representations of the parent Pm3m space-group symmetry which, given the weakly first-order character of the transition, appear to be strongly coupled. Parametric and sequential refinements of the temperature-dependent structure were conducted using four model types: (1) traditional atomic xyz coordinates for each atom, (2) traditional rigid-body parameters, (3) purely displacive symmetry modes and (4) rigid-body rotational symmetry modes. We demonstrate that rigid-body rotational symmetry modes are an especially effective parameter set for the Rietveld characterization of phase transitions involving polyhedral rotations. [ABSTRACT FROM AUTHOR]

For SiBr4 no crystal structures have been reported yet. In this work the crystal structures of SiBr4 were predicted by global lattice-energy minimizations using force-field methods. Over an energy range of 5 kJ mol-1 above the global minimum ten possible structures were found. Two of these structures were experimentally determined from X-ray synchrotron powder diffraction data: The low-temperature β phase crystallizes in P21/c, the high-temperature a phase in Pa3¯. Temperature- dependant X-ray powder diffraction shows that the phase transition occurs at 168 K. [ABSTRACT FROM AUTHOR]

We present a (re)investigation of the hexaoxometalates Li8MO6 (M = Sn, Pb, Zr, Hf) and Li7MO6 (M = Nb, Ta, Sb, Bi). Lithium motion and ionic conductivity in the hexaoxometalates were studied using impedance spectroscopy (for Li7MO6, M = Sb, Bi, Ta) and 3Li and 7Li solid-state nuclear magnetic resonance (for Li7TaO6). The NMR data indicate a considerable exchange of Li among the tetrahedral and octahedral voids even at ambient temperature. In an investigation of the crystal structures using laboratory and synchrotron X-ray powder diffraction techniques, the structures of Li7TaO6, Li7NbO6, and Li7SbO6 could be solved and refined. All three reveal a triclinic metric (Li7SbO6, triclinic, P1macr;, a = 5.38503(6) Å3, b = 5.89164(7) Å, c = 5.43074(6) Å, α = 117.2210(6)°, β = 119.6311(6)°, γ = 63.2520(7)°, V = 127.454(3) Å 3, Z = 1; Li7NbO6, triclinic, P1macr;, a = 5.37932(9) Å, b = 5.91942(11) Å, c = 5.37922(9) Å, α = 117.0033(9)°, β = 119.6023(7)°, γ = 63.2570(9)°, V= 126.938(4) Å3, Z = 1; Li7TaO6, triclinic, P1macr;, a = 5.38486(2) Å, b = 5.92014(3) Å, c = 5.38551(2) Å, α = 117.0108(2)°, β = 119.6132(2)°, γ = 63.2492(2)°, V= 127.208(1) Å3, Z= 1. [ABSTRACT FROM AUTHOR]

Na3PO2S2 was synthesized from the corresponding undecahydrate by freeze–drying. It dismutates at temperatures above 350 °C into Na3PO3S and Na3POS3. The crystal structure of Na3PO2S2 was determined from X-ray powder diffraction data, and refined using the Rietveld technique (Pbca, a=17.5359(2) A˚, b=11.3044(1) A˚, c=5.8656(1) A˚, RF2=8.45%, Rp=4.80%, Rwp=6.79%). The baricenters of the PO2S2-tetrahedra are arranged in the sense of a hexagonal close packing. One of the P&z.sbnd;O bonds of these tetrahedra is oriented parallel to the crystallographic c-axis with the POS2-groups in an eclipsed mutual orientation. The crystal structure of Na3PO2S2 displays a close relationship to the ones of Ca3CrN3 and Na3POS3. Above 330 °C, Na3PO2S2 can be regarded as a fast ionic conductor (with σ>10−5 S cm−1). [Copyright &y& Elsevier]

The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH[sub 3])[sub 3]][sub l][Si(CH[sub 3])[sub 3]][sub 3] (Bu1), and di-tert-butyl-bis(trimethylsilyl)silane, Si[C(CH[sub 3])[sub 3]][sub 2][Si(CH[sub 3])[sub 3]][sub 2] (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm&3macr;m symmetry (Z=4) with a = 13.2645 (2) Å, V = 2333.87 (4) ų for Bul and a = 12.9673 (1) Å, V = 2180.46 (3) ų for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at tempera- tures T[sub c] = 230 (5) K (Bu1) and T[sub c] = 250 (5) K (Bu2) into monoclinic structures with space group P2[sub 1]/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) Å, γ = 109.477(4)°, V= 4172.7 (8) ų and Z=8 for Bu1 and a = 17.0089 (9), b = 15.3159 (8), c = 15.9325 (8) Å, γ = 110.343 (3)°, V= 3891.7 (5) ų and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13-0.28 GPa for Bul and 0.20-0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependen- cies of the lattice parameters were observed. These anomalies are explained as additional disorder-order phase transitions. [ABSTRACT FROM AUTHOR]

The pressure dependence of the crystal structure of cubic tetrakis(trirnethylsilvl)methane C[Si(CH3)3]4 (TC) (P < 16.0 GPa, T = 298 K) is reported using high-resolution angle-dispersive X-ray powder diffraction. The compound has crystal structures with the molecules in a cubic-close- packed (c.c.p.) arrangement. It shows three phase transitions in the measured pressure range. At ambient conditions, TC has space group Pm&macr3;m (Z = 4) with a = 12.8902 (2) Å. V = 2141.8 (1) ų (phase I). Between 0 and 0.13 GPa TC exhibits a first-order phase transition into a structure with space group Pa&macr3; (phase II).. A second first-order phase transition occurs between 0.2 and 028 GPa into a structure with space group P213 (phase III). Under non-hydrostatic pressure conditions (P > 10 GPa) a transformation is observed into a c.c.p. structure that is different from the face-centred-cubic structure at ambient conditions. A non-linear compression behaviour is observed, which could be described by a Vinet relation in the range 0.28-4.8 GPa. The extrapolated bulk modulus of the high-pressure phase III was determined to be K0 = 7.1 (8) GPa. The crystal structures in phase III are refined against X-ray powder data measured at several pressures between 0.49 and 4.8 GPa, and the molecules are found to be fully ordered. This is interpreted to result from steric interactions between neighbouring molecules, as shown by analysing the pressure dependence of intramolecular angles, torsion angles and intermolecular distances. Except for their cell dimensions, phases I. II and III are found to be isostructural to the corresponding phases at low temperatures. [ABSTRACT FROM AUTHOR]

Reports that the compounds tetrakis(trimethylsilyl)methane (TC) and tetrakis(trimethylsilyl)silane (TSi) have crystal structures with the molecules in a cubic closed-packed stacking. Space group at room temperature of both structures; Description of an X-ray scattering data by a molecule with approximately sixfold orientational disorder, ruling out structure with free rotating molecules.

The self‐propulsion of single crystals of three Zn(II) complexes under UV light is described by P. Naumov, J. J. Vittal et al. in their Communication on page 5907 ff. This visually impressive dynamic behavior is a consequence of the accumulation and sudden release of strain created by crystal expansion following the formation of 1D coordination polymers by a [2+2] cycloaddition reaction. Understanding this effect, which is mechanistically analogous to the bursting of popcorn in a hot pan, may help in the design of new light‐driven mechanical actuators. [ABSTRACT FROM AUTHOR]

The crystal structure of the title compound, disodium 1,2,3,4-tetra­oxo-5-cyclo­hexene-5,6-diolate, 2Na+·C6O62−, is built up of alternating layers of hexa­gonally packed Na+ cations and rhodizonate dianions. The rhodizon­ate dianion has a slightly twisted conformation. [ABSTRACT FROM AUTHOR]

White efflorescence crystals grown on the surfaces of a bronze bowl, classical ceramic and ancient wine jugs were investigated. X-ray powder diffraction (XRPD) revealed that in each case an identical, hitherto unknown phase was formed. The crystal structure was solved from high resolution XRPD measurements and revealed a phase composition of Ca 2 (CH 3 COO)(HCOO)(NO 3 ) 2 ·4H 2 O, which is in accordance with the complementary analysis. The overall structural motif of Ca 2 (CH 3 COO)(HCOO)(NO 3 ) 2 ·4H 2 O, one dimensional calcium carboxylate zig zag chains in which acetate and formate ions are arranged in an alternating fashion, is closely related to other naturally occurring or artificial efflorescence salts like thecotrichite or calclacite. [ABSTRACT FROM AUTHOR]