Volume 227, Issue 2 -

The crystal structure of the low temperature phase of bis(hexylammonium) zirconium bis(nitrilotriace-tate) dihydrate was investigated at 100 K by means of X-ray single crystal diffraction. Although the zirconium bis(nitrilotriacetate) anion representing the dominant part of the crystal structure shows only minor changes during the phase transition, a strong change in respect to the oriäentation of the hexylammonium cations takes place. These are now statically disordered over two geometrically quite different conformations at 100 K. The distance between the terminal carbon atoms of the two possible conformations of the hexylammonium cation is as large as 5.7 Å. The space group remains C 2/ c after passing the phase transition from the high temperature phase to the low temperature phase with the lattice parameters a = 18.8708 (6) Å, b = 11.2229 (3) Å, c = 16.1895 (5) Å, β = 112.726 (1)°. In addition heat capacity measurements were performed, which yielded broad peaks at about 275 K indicating the phase transition temperature T c .

The lattice dynamics of α -quartz has been studied in great details by combining inelastic X-ray scattering (IXS) from single- and polycrystalline samples, 3D mapping of thermal diffuse scattering (TDS) and ab initio calculations. Pronounced features in TDS patterns have been identified and the origin of first peak in vibrational density of states is unambiguously revealed.

Crystal-chemistry of Fe 3 (PO 4 ) 2 · 8 H 2 O vivianite minerals was investigated by means of a multi-methodological approach based on electron microprobe analysis in wavelenght dispersive mode, single-crystal X-ray diffraction and infrared spectroscopy. To this aim, three specimens coming from Commentry (France) ( 1 ), Settefrati (Frosinone, Italy) ( 2 ) and Ibex Mine (Colorado, USA) ( 3 ), have been subject to EMPA analysis, indicating chemical composition (Fe 2.94 Mg 0.06 Mn 0.01 ) Σ3.02 (P 1.99 O 8 ) · 8 H 2 O ( 1 ), (Fe 2.96 Mg 0.01 Mn 0.04 ) Σ3.01 ((P 1.96 Si 0.03 Al 0.02 ) Σ2.01 O 8 ) · 8 H 2 O ( 2 ) and (Fe 2.65 Zn 0.27 Mn 0.06 Na 0.03 Mg 0.02 ) Σ3.03 (P 1.99 O 8 ) · 8 H 2 O ( 3 ); successively they have been subject to structural refinement by means of single-crystal X-ray diffraction within monoclinic space group C 2/ m , with the following unit cell constants: a = 10.100(3), b = 13.494(3), c = 4.709(3) Å; β = 104.24(4)° and V = 622.1(7) Å 3 ( 1 ); a = 10.116(3); b = 13.473(3), c = 4.7064(7) Å; β = 104.33(4)° and V = 621.5(2) Å 3 ( 2 ); a = 10.083(2), b = 13.468(2), c = 4.718(1) Å, β = 104.47(2)° and V = 620.3(2) Å 3 ( 3 ). Iron cations occupy two special positions, making up single and dimerical octahedral groups, joined by (PO 4 ) tetrahedra groups, in order to form infinite layers down b , making up, via consistent O—H … O hydrogen bonds, the three-dimensional framework. The present vivianite samples were subject to geochemical and crystal chemical comparisons, the latter also by means of bond valence analysis with literature available phases. Last, IR spectra were performed for the three phases, in order to provide information on bending and stretching modes of the minerals, as well as to investigate H bonds by means of Libowitzki formula application.

In this paper, we present a structural model for the M 1 polymorph of tricalcium silicate Ca 3 SiO 5 from Powder X-Ray Diffraction (XRD) data, including weak intensity superstructure Bragg lines. As no single crystal is available, this structural model has been deduced using the structural relationships found between the previously known triclinic and monoclinic M 3 polymorphs. We find that the better starting set of atomic positions for Rietveld refinement is the triclinic set and not the monoclinic set. A key observation is that the monoclinic M 1 structure is closer to the low temperature triclinic T 3 structure (within the Golovastikov model) than to the higher temperature monoclinic M 3 structure. The unit cell and the set of atomic positions of the two best models, called 3〈 M 〉 Pc and 3〈 T 〉 Pn models, are provided. We prefer the 3〈 M 〉 Pc model for it better reproduces the weak characteristic Bragg lines of the superstructure.

Routine X-ray single-crystal structure analysis of Na[C 6 H 4 ClO 3 S]·H 2 O resulted in an orthorhombic layer structure with space group Pnma , Z =4. In this crystal structure the phenyl rings in a single layer are disordered over two mutually perpendicular orientations with occupancies of 0.500(4) each. Structure determination including superstructure reflections and irregular shaped reflections revealed a twinned, ordered, monoclinic structure, P 2 1 / c , Z =8. Here, within a layer the phenyl rings are arranged alternatingly perpendicular. Pair distribution function analysis (PDF) and lattice-energy calculations confirmed this arrangement. Faint diffuse scattering streaks point to a one-dimensional disorder (concerning the layer-stacking sequence). Application of the order-disorder (OD) approach led to three polytype structures with maximum degree of order (MDO); one of them is the experimental monoclinic structure. This structure was found to have the most favourable energy in the lattice-energy minimisations. However, the energy differences between different polytypes with different stacking sequences are rather small. Hence, the lattice-energy minimisations confirmed the monoclinic P 2 1 / c structure with stacking disorder.

The vagaries of recrystallisation are highlighted in this contribution which describes the full characterisation of crystals isolated from the recrystallisation of [Cu 2 L 4 (EtOH) 2 ] from a 1 : 2 mixture of DMSO and CHCl 3 (v/v); L is 4-nitrobenzoate. Slow evaporation over four weeks yielded blue-green crystals of 1 that were shown to be a rare example of a three-component co-crystal comprising [CuL 2 (OH 2 )(DMSO)] 2 , [CuL 2 (OH 2 ) 2 (DMSO)] and [CuL 2 (OH 2 )(DMSO) 2 ] in the ratio 1 : 2 : 2. After crystals of 1 were removed from the solution, blue crystals of 2 were isolated after another week had elapsed. These proved to be [CuL 2 (OH 2 )(DMSO) 2 ] and to be the trans -DMSO isomer of one of the components of 1 . The supramolecular aggregation in each crystal structure features ten-membered {…HOH…OCOCuOCO} synthons whereby the hydrogen atoms of a water molecule link two carbonyl-O atoms of another complex molecule. In 1 , these synthons lead to an isolated six-copper aggregate, and in 2 , these lead to supramolecular chains. IR and thermal analysis (TGA and DSC) data are also presented. Crystal data for ( 1 ): triclinic, P -1, a = 13.9035(4), b = 15.5305(4), c = 15.7069(4) Å, α = 80.062(2), β = 83.174(2), γ = 70.109(2)°, V = 3134.75(15)Å 3 , Z = 2, R = 0.036. Crystal data for ( 2 ): monoclinic, C 2/ c, a = 30.0180(16), b = 5.8440(3), c = 14.2639(8) Å, β = 114.669(7)°, V = 2273.9(2) Å 3 , Z = 4, R = 0.027.