Single-crystal Synchrotron Radiation Research Articles

First platinum(ii)–alkaline-earth acetate-bridged complexes Ptii(m-OAc)4Mii(AcOH)4 (M = Ca, Sr, Ba)

The first platinum(ii)–alkaline-earth acetate-bridged complexes Ptii(m-OAc)4Mii(AcOH)4 (M = Ca, Sr, Ba) were synthesized, structurally characterized using single-crystal synchrotron radiation X-ray diffraction analysis and tested for catalytic performance in homogeneous styrene hydrogenation under mild conditions.

Temperature- and Pressure-Induced Spin Crossover in Co1+xCr2-xSe4 (x = 0.24): A Diffraction Study.

The Co(2+) ions of the Co1+xCr2-xSe4 phase (Co1.24Cr1.76Se4 composition with x = 0.24, C2/m space group, Cr3S4-type structure) undergo a high- to low-spin-state transition around 230 K, as concluded from the temperature-dependent single-crystal synchrotron radiation diffraction experiments and the previously reported physical property studies. The change of the spin state is not instantaneous and goes through a wide spin-crossover (SCO) region of 75 K. A similar Co(2+) high- to low-spin-state transition is suggested at a pressure of 14.5 GPa, as is evident from the pressure-dependent single-crystal synchrotron radiation diffraction experiments. The corresponding SCO region is equal to 5 GPa, and the structural behavior is different from the one observed during the temperature-dependent transition. Coupling between the spin-conversion process in Co1+xCr2-xSe4 and the concomitant changes in the physical properties opens a way for a controlled tuning of the observed physical response through compositional and structural modifications.

The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions

We simulated the redox decomposition of magnesium-siderite at pressures and temperatures corresponding to the top of the Earth’s D″ layer (135 GPa and 2650 K). It transforms into new phases, with unexpected stoichiometry. We report their crystal structure, based on single-crystal synchrotron radiation diffraction on a multi-grain sample, using a charge-flipping algorithm. Mg2Fe2(C4O13) is monoclinic, a = 9.822(3), b = 3.9023(13), c = 13.154(5) A, β = 108.02(3)°, V = 479.4(3) A3 (at 135 GPa). It contains tetrahedrally coordinated carbon units, corner-shared in truncated C4O13 chains. Half of the cations are divalent, and half trivalent. The carbonate coexists with a new iron oxide, Fe13O19, monoclinic, a = 19.233(2), b = 2.5820(13), c = 9.550(11) A, β = 118.39(3)°, V = 417.2(5) A3 (at 135 GPa). It has a stoichiometry between hematite, Fe2O3, and magnetite, Fe3O4. The formation of these unquenchable phases indicates, indirectly, the formation of reduced-carbon species, possibly diamond. These structures suggest the ideas that the mineralogy of the lower mantle and D″ region may be more complex than previously estimated. This is especially significant concerning accessory phases of fundamental geochemical significance and their role in ultra-deep iron-carbon redox coupling processes, as well as the iron-oxygen system, which certainly play an important role in the lower mantle mineral phase equilibria.

Innsbruckite, Mn33(Si2O5)14(OH)38 – a new mineral from the Tyrol, Austria

AbstractA description of the new mineral innsbruckite, Mn33(Si2O5)14(OH)38, a hydrous manganese phyllosilicate found in Tyrol, Austria is given. The crystal structure was determined by singlecrystal synchrotron radiation diffraction experiments at the X06DA beamline at the Swiss Light Source (Paul Scherrer Institute, Villigen, Switzerland). The space group is Cm and lattice parameters are a = 17.2760(19), b = 35.957(5), c = 7.2560(8) Å , β = 91.359(7)º, V = 4506.1(10) Å3, Z = 2. Innsbruckite belongs to the group of modulated 1:1 layer silicates and is chemically and structurally quite closely related to bementite, Mn7(Si2O5)3(OH)8. The chemical analysis revealed a close to ideal composition with only minor amounts of Al, Fe and Mg. Using Liebau’s nomenclature for silicate classification the silicate anion can be described as an unbranched siebener single layer. Innsbruckite shows a complex topology of the silicate sheet, exhibiting 4-, 5-, 6- and 8-membered rings. The silicate sheet is fully characterized using vertex symbols, and its topology is compared to those in other complex sheet silicates. Furthermore, the structural investigation is complemented with Raman spectroscopic studies.

Oxyfadichalcones A–C: three chalcone dimers fused through a cyclobutane ring from Tibetan medicine Oxytropis falcata Bunge

Oxyfadichalcones A and B, two unprecedented chalcone dimers fused through a cyclobutane ring by head-to-tail [2+2] cycloaddition of two chalcones that had never been found previously in nature, along with oxyfadichalcone C, a new head-to-head [2+2] cyclized chalcone dimer, were simultaneously obtained from Oxytropis falcata. Structural elucidation was succeeded by spectroscopic and single-crystal synchrotron radiation analysis. Additionally, the photosynthesis of the chalcone dimers was performed and the plausible biosynthesis was discussed.

The crystal structure of sacrofanite, the 74 Å phase of the cancrinite–sodalite supergroup

Sacrofanite, a = 12.903(2) Å, c = 74.284(8) Å, space group P 6 ¯ 2 c , belongs to the cancrinite–sodalite supergroup of minerals, and displays a 28-layer stacking sequence along the c axis. Its stacking sequence is ABCABACACABACBACBACABABACABC…, where A, B and C stand for the positions of six-member rings of tetrahedra in each layer. It corresponds to the Zhdanov symbol |12(8)21|12(8)21|, and gives rise to a framework with topological symmetry P6 3/ mmc. The ordering of Si and Al in the tetrahedral sites reduces the symmetry to P 6 ¯ 2 c . The members of this supergroup of minerals belong to the wider ABC-6 family, where also double rings of tetrahedra may occur. They share many structural features with zeolites, showing structural cages hosting extra-framework ions as well as H 2O molecules. The crystal structure of sacrofanite has been modelled on the basis of High Resolution Transmission Electron Microscopy (HRTEM) images. The resulting model has been successfully refined by using both single-crystal synchrotron radiation and laboratory data. The refinements converged to R = 0.083 for 4228 unique reflections, and to R = 0.096 for 15,795 unique reflections, respectively. The resulting framework is formed by eight cancrinite and four sodalite cages superimposed along [0, 0, z], whereas one cancrinite, four sodalite, two losod, and one liottite cages occur along [1/3, 2/3, z] and [2/3, 1/3, z]. The structural formula of sacrofanite, as obtained from the refinement and by crystal chemical considerations, is (Na 61K 19Ca 32) ∑=112(Si 84Al 84O 336)(SO 4) 26Cl 2F 6·2H 2O.

A 2D [Fe II-bistetrazole] coordination polymer exhibiting spin-crossover properties

The reaction of 1,3-bis(tetrazol-1-yl)-2-propanol (btzpol) with Fe(BF 4) 2 · 6H 2O in acetonitrile yields the remarkable 2D coordination polymer [Fe II(btzpol) 1.8(btzpol-OBF 3) 1.2](BF 4) 0.8 · (H 2O) 0.8(CH 3CN) ( 1). This compound has been structurally characterized using an X-ray single-crystal synchrotron radiation source. The iron(II) centers are bridged by means of double btzpol bridges along the c direction, and by single btzpol bridges along the b direction. The reaction of part of the ligand with the counterion has forced the compound to crystallize in this extended two dimensional structure. The compound shows spin-transition properties, both induced by temperature and light, with T 1/2 = 112 K and T( LIESST) = 46 K, respectively. The relaxation of the metastable high-spin state created by irradiation is exponential, following an Arrhenius type behavior at high temperature, and dominated by a temperature independent tunneling process at lower temperatures.

Synthesis, Physical Properties, Multitemperature Crystal Structure, and 20 K Synchrotron X-ray Charge Density of a Magnetic Metal Organic Framework Structure, Mn3(C8O4H4)3(C5H11ON)2

A new magnetic metal organic framework material has been synthesized, Mn3(C8O4H4)3(C5H11ON)2, 1. Magnetic susceptibility measurements from 2 to 400 K reveal anti-ferromagnetic ordering at approximately 4 K and a total magnetic moment of 6.0 micro(B). The magnetic phase transition is confirmed by heat capacity data (2-300 K). The crystal structure is studied by conventional single-crystal X-ray diffraction data at 300, 275, 250, 225, 200, 175, 150, 125, and 100 K, and synchrotron data at 20 K. There is a phase transition between 100 and 20 K due to ordering of the diethylformamide molecules. The X-ray charge density is determined based on multipole modeling of a second 20 K single-crystal synchrotron radiation data set. The electron distributions around the two unique Mn centers are different, and both have substantial anisotropy. Orbital population analysis reveals large electron donation (1.7 e) to each Mn atom and the maximum possible number of unpaired electrons is 3.2 for both Mn sites. Thus, there is a considerable orbital component to the magnetic moment. Bader topological analysis shows an absence of Mn-Mn bonding, and the magnetic ordering is via super-exchange through the oxygen bridges. Formal electron counting suggests Mn2+ sites, but this is not supported by the Bader atomic charges, Mn1 = +0.11 e, Mn2 = +0.17 e. The topological measures show the dominant metal-ligand interactions to be electrostatic, and a simple exponential correlation is derived between Mn-O bond lengths and the values of nabla2rho at the bond critical points.

Single-Crystal Synchrotron Radiation X-ray Diffraction Study of B and Ga Silicalites Compared to a Purely Siliceous MFI: A Discussion of the Heteroatom Distribution

We report the structure determinations, obtained by synchrotron radiation single-crystal X-ray diffraction experiments, of as-synthesized orthorhombic MFI boron and gallium silicalites compared to that of an unsubstituted defect-free silicalite. The synthesis in fluoride medium yielded comparatively large twinned single crystals. The absence of any measurable signal due to Si(OH) species in the 29Si NMR spectra of silicalite (Fonseca, A.; Nagy, J. B.; El Hage-Al Asswad, J.; Mostowicz, R.; Crea, F.; Testa, F. Zeolites 1995, 15, 259) indicates that their defectivity is very low because these samples are almost free of Si vacancies, which are usually rather common in MFI materials. All carbon and nitrogen atoms of the disordered tetrapropylammonium (TPA+) template molecules have been located. These molecules, located at the intersection of the straight and sinusoidal channels, are similar to those found by Van Koningsveld et al. (Van Koningsveld, H.; Van Bekkum, H.; Jansen, J. C. Acta Crystallogr., Sect. B 1...

Thermal annealing of metamict titanite: A synchrotron radiation and optical birefringence study

The thermal annealing behaviour of metamict titanite from Cardiff, Canada, which shows moderate structural damage from the a-decay of radiogenic elements (U, Th) has been studied using single-crystal synchrotron radiation and optical-birefringence techniques. Progressive and isothermal annealing experiments yield a temperature-dependent response in the diffraction and optical signals. The low-temperature regime (< 673 K) is characterized by a preferred annealing of Frenkel-defects which results in small changes of the unit-cell volume and the Bragg-intensities on a time-scale of several hours. On constant heating at higher temperatures, metamict titanite displays two-stage kinetics with most rapid effects during the first two hours of annealing and less significant changes after the initial annealing period. Fast annealing of Frenkel defects occurs first, followed by recrystallization of more damaged regions. Single-crystal studies reveal lower temperatures for pronounced annealing effects than previously reported in powder-diffraction studies (ca. 100 K).

Low-Temperature Synchrotron Radiation Study of a Twinned Disordered Crystal of Bis(4,4'-bromophenyl)-61,61-diyl Methano Fullerene C60

Synchrotron radiation diffraction measurements at 100 (5) K have been carried out on bis(4,4′-bromophenyl)-61,61-diyl methano fullerene C60 using area detector technology. In order to obtain a satisfactory description of the data it is necessary to introduce both a twinning model of the crystal and a disorder model consisting of two different isomers of the title compound. The study provides the first solid-state characterization of a 6–5 isomer of a methano fullerene. For the 6–6 isomer the geometry is in good agreement with recent literature on methano fullerenes. Unfortunately, the present study cannot resolve the bond lengths in the transannular region. The fact that the structure can be solved from diffraction data measured on a minute poorly scattering crystal shows that the low-temperature single-crystal synchrotron radiation technique is an indispensable tool in chemical crystallography.

A magnetic x-ray diffraction investigation of gadolinium selenide

A single-crystal synchrotron radiation study of gadolinium selenide has been made in the temperature range 15 - 100 K. GdSe has the rocksalt structure and becomes antiferromagnetic below a reported Néel temperature of 65 K. At 15 K, magnetic reflections are observed at with modulation wavevector propagating from reciprocal lattice point G. This is achieved by exploiting the resonant enhancement in the vicinity of the and edges. Similar enhancements are observed at the two edges, with the maximum effect occurring approximately 3 eV above the absorption edge. The temperature dependence of the intensity of the magnetic reflections indicates a Néel temperature of 63(1) K. These measurements, together with high-resolution studies of the fundamental reflections , contribute further evidence of magnetic or structural changes in the sample at 37(1) K. Our observations are discussed and compared with previous x-ray diffraction and magnetic susceptibility measurements.