Structure and stability of BaTiSi2O7.

Due to their optical, photo-luminescence (PL), and afterglow properties, barium titanosilicates are compounds of great interest for functional materials and light-emitting devices. Among them, BaTiSi2O7 (BTS2) is certainly one of the most intriguing; it displays peculiar properties (e.g. PL orange emission) whose exhaustive explanation has been hampered to date by the lack of a structure model. In this work, BTS2 and the related compound BaTiSi4O11 (BTS4) were synthesized through conventional solid-state reaction methods. BTS2 invariably shows complex twinning patterns. Thus, its structure solution and Rietveld structure refinement were attempted using synchrotron powder diffraction. BTS2 was found to be an intergrowth of monoclinic and triclinic crystals. The monoclinic phase has the space group P21/n and unit cell a = 7.9836 (3), b = 10.0084 (4), c = 7.4795 (3) Å, and ß = 100.321 (3)°, whereas the triclinic phase has the space group P\bar 1 and unit cell a = 7.99385 (4), b = 10.01017 (5), c = 7.47514 (3) Å, α = 90.084 (8), ß = 100.368 (8) and γ = 89.937 (9)°. These lattices can be seen as a distortion of that of tetragonal synthetic ß-BaVSi2O7 with Ti in place of V. The structure models obtained from this study confirm the presence of fivefold coordinated Ti atoms in a distorted pyramidal configuration. The proposed solution supports existing theories for the explanation of the PL orange colour in BTS2.

Analysis of an industrial production suspension of Bacillus lentus subtilisin crystals by powder diffraction: a powerful quality-control tool.

A microcrystalline suspension of Bacillus lentus subtilisin (Savinase) produced during industrial large-scale production was analysed by X-ray powder diffraction (XRPD) and X-ray single-crystal diffraction (MX). XRPD established that the bulk microcrystal sample representative of the entire production suspension corresponded to space group P212121, with unit-cell parameters a = 47.65, b = 62.43, c = 75.74 Å, equivalent to those for a known orthorhombic crystal form (PDB entry 1ndq). MX using synchrotron beamlines at the Diamond Light Source with beam dimensions of 20 × 20 µm was subsequently used to study the largest crystals present in the suspension, with diffraction data being collected from two single crystals (∼20 × 20 × 60 µm) to resolutions of 1.40 and 1.57 Å, respectively. Both structures also belonged to space group P2(1)2(1)2(1), but were quite distinct from the dominant form identified by XRPD, with unit-cell parameters a = 53.04, b = 57.55, c = 71.37 Šand a = 52.72, b = 57.13, c = 65.86 Å, respectively, and refined to R = 10.8% and Rfree = 15.5% and to R = 14.1% and Rfree = 18.0%, respectively. They are also different from any of the forms previously reported in the PDB. A controlled crystallization experiment with a highly purified Savinase sample allowed the growth of single crystals of the form identified by XRPD; their structure was solved and refined to a resolution of 1.17 Šwith an R of 9.2% and an Rfree of 11.8%. Thus, there are at least three polymorphs present in the production suspension, albeit with the 1ndq-like microcrystals predominating. It is shown how the two techniques can provide invaluable and complementary information for such a production suspension and it is proposed that XRPD provides an excellent quality-control tool for such suspensions.

Towards accurate structural characterization of metal centres in protein crystals: the structures of Ni and Cu T(6) bovine insulin derivatives.

Using synchrotron radiation (SR), the crystal structures of T6 bovine insulin complexed with Ni(2+) and Cu(2+) were solved to 1.50 and 1.45 Šresolution, respectively. The level of detail around the metal centres in these structures was highly limited, and the coordination of water in Cu site II of the copper insulin derivative was deteriorated as a consequence of radiation damage. To provide more detail, X-ray absorption spectroscopy (XAS) was used to improve the information level about metal coordination in each derivative. The nickel derivative contains hexacoordinated Ni(2+) with trigonal symmetry, whereas the copper derivative contains tetragonally distorted hexacoordinated Cu(2+) as a result of the Jahn-Teller effect, with a significantly longer coordination distance for one of the three water molecules in the coordination sphere. That the copper centre is of type II was further confirmed by electron paramagnetic resonance (EPR). The coordination distances were refined from EXAFS with standard deviations within 0.01 Å. The insulin derivative containing Cu(2+) is sensitive towards photoreduction when exposed to SR. During the reduction of Cu(2+) to Cu(+), the coordination geometry of copper changes towards lower coordination numbers. Primary damage, i.e. photoreduction, was followed directly by XANES as a function of radiation dose, while secondary damage in the form of structural changes around the Cu atoms after exposure to different radiation doses was studied by crystallography using a laboratory diffractometer. Protection against photoreduction and subsequent radiation damage was carried out by solid embedment of Cu insulin in a saccharose matrix. At 100 K the photoreduction was suppressed by ∼15%, and it was suppressed by a further ∼30% on cooling the samples to 20 K.

Strontium localization in bone tissue studied by X-ray absorption spectroscopy.

Strontium has recently been introduced as a pharmacological agent for the treatment and prevention of osteoporosis. We determined the localization of strontium incorporated into bone matrix from dogs treated with Sr malonate by X-ray absorption spectroscopy. A new approach for analyzing the X-ray absorption spectra resulted in a compositional model and allowed the relative distribution of strontium in the different bone components to be estimated. Approximately 35-45% of the strontium present is incorporated into calcium hydroxyapatite (CaHA) by substitution of some of the calcium ions occupying highly ordered sites, and at least 30% is located at less ordered sites where only the first solvation shell is resolved, suggesting that strontium is surrounded by only oxygen atoms similar to Sr(2+) in solution. Strontium was furthermore shown to be absorbed in collagen in which it obtains a higher structural order than when present in serum but less order than when it is incorporated into CaHA. The total amount of strontium in the samples was determined by inductively coupled plasma mass spectrometry, and the amount of Sr was found to increase with increasing dose levels and treatment periods, whereas the relative distribution of strontium among the different components appears to be independent of treatment period and dose level.

The structures of T6, T3R3 and R6 bovine insulin: combining X-ray diffraction and absorption spectroscopy.

The crystal structures of three conformations, T(6), T(3)R(3) and R(6), of bovine insulin were solved at 1.40, 1.30 and 1.80 Å resolution, respectively. All conformations crystallized in space group R3. In contrast to the T(6) and T(3)R(3) structures, different conformations of the N-terminal B-chain residue PheB1 were observed in the R(6) insulin structure, resulting in an eightfold doubling of the unit-cell volume upon cooling. The zinc coordination in each conformation was studied by X-ray absorption spectroscopy (XAS), including both EXAFS and XANES. Zinc adopts a tetrahedral coordination in all R(3) sites and an octahedral coordination in T(3) sites. The coordination distances were refined from XAS with a standard deviation of <0.01 Å. In contrast to the distances determined from the medium-resolution crystal structures, the XAS results were in good agreement with similar coordination geometries found in small molecules, as well as in other high-resolution insulin structures. As the radiation dose for XRD experiments is two orders of magnitude higher compared with that of XAS experiments, the single crystals were exposed to a higher degree of radiation damage that affected the zinc coordination in the T(3) sites in particular. Furthermore, XANES spectra for the zinc sites in T(6) and R(6) insulin were successfully calculated using finite difference methods and the bond distances and angles were optimized from a quantitative XANES analysis.

Polymeric strontium ranelate nona-hydrate.

The title compound, poly[[µ-aqua-tetra-aqua{µ-5-[bis-(carboxyl-atometh-yl)amino]-3-carboxyl-atomethyl-4-cyano-thio-phene-2-carboxyl-ato}distrontium(II)] tetra-hydrate], [Sr(2)(C(12)H(6)N(2)O(8)S)(H(2)O)(5)]·3.79H(2)O, crystallizes with nine- and eight-coordinated Sr(2+) cations. They are bound to seven of the eight ranelate O atoms and five of the water mol-ecules. The SrO(8) and SrO(9) polyhedra are inter-connected by edge-sharing, forming hollow layers parallel to (011). The layers are, in turn, inter-connected by ranelate anions, forming a metal-organic framework (MOF) structure with channels along the a axis. The four water mol-ecules not coordinated to strontium are located in these channels and hydrogen bonded to each other and to the ranelates. Part of the water H atoms are disordered. The compound dehydrates very easily and 0.210 (4) water mol-ecules out of nine were lost during crystal mounting causing additional disorder in the water structure.

Synthesis of erbium oxide nanosheets and up-conversion properties.

A novel erbium-based compound as well as Er(2)O(3) nanosheets have been synthesized through a simple hydrothermal route. The nanosheets are of 200 nm width and 10-15 nm thickness. It is suggested that this erbium-based compound has a possible formula of Er(2)O(5)H(4) with a primitive tetragonal structure (cell parameters: a = 8.465(1) and c = 15.117(2) Å). Face-centered cubic and body-centered cubic structured Er(2)O(3) nanosheets were obtained after calcination of this compound at 623 and 973 K, respectively, both having a paramagnetic behavior. Er(2)O(5)H(4) and Er(2)O(3) nanosheets have similar up-conversion properties with strong blue emission, which is rarely reported in the literature. The existence of absorbed surface contaminations in nanosheets might be the origin for the blue emission enhancement.

Structure of caesium disulfate at 120 and 273 K.

The crystal structures of Cs2S2O7 at 120 and 273 K have been determined from X-ray single-crystal data. Caesium disulfate represents a new structure type with a uniquely high number of independent formula units at 120 K: In one part caesium ions form a tube surrounding the disulfate ions, [Cs8(S2O7)6+]n; in the other part a disulfate double-sheet sandwiches a zigzagging caesium ion chain, [Cs2(S2O7)6-]n. Caesium disulfate shows an isostructural order-disorder transition between 230 and 250 K, where two disulfate groups become partially disordered above 250 K. The Cs+-ion arrangement shows a remarkable similarity to the high-pressure Rb(IV) metal structure.

Structures of strontium diformate and strontium fumarate. A synchrotron powder diffraction study.

The crystal structures of strontium diformate in space groups P2(1)2(1)2(1) (alpha form, 295 K), P4(1)2(1)2 (beta form, 334 and 540 K) and I4(1)/amd (delta form, 605 K), and strontium fumarate in space groups Fddd (beta form, 105 K) and I4(1)/amd (alpha form, 293 K) have been determined from synchrotron X-ray powder diffraction data. Except for the alpha-strontium diformate, all the structures are based on a diamond-like Sr-ion arrangement, as in strontium acetylene dicarboxylate. The formate ions are disordered in the delta phase owing to steric hindrance. The fumarate ions are disordered over four (alpha) or two (beta) symmetry-equivalent orientations. alpha-Strontium fumarate crystallizes with a unique 90 degree carboxylate dihedral angle, and is stable up to 773 K.

Octa-rubidium di-µ-sulfato-κO:O'-bis-[cis-dioxido-cis-disulfatotungstate(VI)].

The title compound, Rb(8)[W(2)O(4)(SO(4))(6)], was precipitated from a melt of tungsten(VI) oxide and rubidium sulfate in rubidium disulfate. The unit cell contains two discrete [{W(VI)O(2)(SO(4))(2)}(2)(µ-SO(4))(2)](8-) units connected by Rb-O coord-ination. The W atom is octahedrally surrounded by two oxide ligands, two terminal sulfate ligands and two bridging sulfate groups. One Rb atom is coordinated by eight O atoms, whereas the three other Rb atoms are coordinated by nine O atoms from sulfate and oxide groups, leading to distorted [RbO(x)] polyhedra.

Ammonium 1-hydroxy-2-(2-pyridinio)ethane-1,1-diyldiphosphonate dihydrate and potassium 1-hydroxy-2-(2-pyridinio)ethane-1,1-diyldiphosphonate dihydrate.

The crystal structures of the title compounds, ammonium risedronate dihydrate, NH4+.C7H10NO7P2-.2H2O, (I), and potassium risedronate dihydrate, K+.C7H10NO7P2-.2H2O, (II), have been determined from single-crystal X-ray data collected at 120 K. Compound (I) forms a three-dimensional hydrogen-bonded network which connects the ammonium and risedronate ions and the water molecules. In compound (II), the K+ ions are seven-coordinated in a capped distorted trigonal prism. The coordination polyhedra form chains by corner-sharing, and these chains are connected by phosphonate groups into layers in the ac plane. The layers are stacked and connected by hydrogen bonds in the b direction. The risedronate conformation is determined by intramolecular interactions fine-tuned by crystal packing effects. All H-atom donors in both structures are involved in hydrogen bonding, with D...A distances between 2.510 (2) and 3.009 (2) A.

Strontium D-glutamate hexahydrate and strontium di(hydrogen L-glutamate) pentahydrate.

[Sr(C5H7NO4)].6H2O, (I), and [Sr(C5H8NO4)2].5H2O, (II), both crystallize with similar strontium-glutamate-water layers. In (I), the neutral layers are connected through hydrogen bonds by water molecules, while in (II), the positively charged layers are connected through hydrogen bonds and electrostatic interactions by interleaving layers of hydrogen glutamate anions and water molecules.

New efficient catalyst for ammonia synthesis: barium-promoted cobalt on carbon.

Barium-promoted cobalt catalysts supported on carbon exhibit higher ammonia activities at synthesis temperatures than the commercial, multipromoted iron catalyst and also a lower ammonia inhibition.

Structural and Quantum Chemical Study of Bi(5)(3+) and Isoelectronic Main-Group Metal Clusters. The Crystal Structure of Pentabismuth(3+) Tetrachlorogallate(III) Refined from X-ray Powder Diffraction Data and Synthetic Attempts on Its Antimony Analogue.

Pentabismuth(3+) tetrachlorogallate(III), (Bi(5)(3+))(GaCl(4)(-))(3), has been synthesized by reducing a BiCl(3)-GaCl(3) melt with bismuth metal and the crystal structure refined from X-ray (Cu Kalpha(1)) powder diffraction data. The structure was found to belong to space group R-3c, with the lattice parameters a = 11.871(2) Å and c = 30.101(3) Å (Z = 6). It is isostructural with the previously characterized Bi(5)(AlCl(4))(3). An attempt to synthesise the antimony analogue Sb(5)(GaCl(4))(3) by reducing a SbCl(3)-GaCl(3) mixture with gallium metal produced a black solid phase. The gallium content of this phase is consistent with the stoichiometry Sb(5)(GaCl(4))(3), and the Raman spectrum of the phase dissolved in SbCl(3)-GaCl(3) comprises strong, low-frequency bands attributable to Sb-Sb stretch vibrations in Sb(5)(3+) or another reduced antimony species. Quantum chemical analyses have been performed for the isoelectronic, trigonal pyramidal closo-clusters Sn(5)(2-), Sb(5)(3+), Tl(5)(7-), Pb(5)(2-), and Bi(5)(3+), both with extended Hückel (eH) and Hartree-Fock (HF) methods. The HF calculations were performed with and without corrections for the local electron-electron correlation using second-order Møller-Plesset perturbation theory (MP2). All theoretical results are compared and evaluted with respect to experimental cluster structures and vibrational frequencies. The results from the calculations agree well with available experimental data for the solid-state structures and vibrational spectra of these cluster ions, except for the Tl(5)(7-) ion. Isolated Tl(5)(7-) is suggested to be electronically unstable because of the high charge density. The Sb(5)(3+) cluster ion is indicated to be stable. According to the calculations, Sn(5)(2-) and Pb(5)(2-) may be described in terms of edge-localized bonds without substantial electron density between the equatorial atoms, whereas Sb(5)(3+) and Bi(5)(3+) have electron density evenly distributed over all M-M vectors. Furthermore, the theoretical results give no support for a D(3h) --> C(4v) fluxionality of these clusters.