Ge32 Co9-x : Creating "Empty" Space by High Pressure.

The compound Ge32 Co9-x (x=0.54(6), a=10.9861(3) Å, space group Im 3 ‾ $\bar 3$ m) prepared under high pressure and at high temperature is metastable under ambient conditions. It crystallizes in a new structure type, Pearson symbol cI82-1.08. The crystal structure represents a slightly distorted cubic primitive arrangement of germanium atoms with part of the Ge cubes filled by cobalt. Analysis of the chemical bonding by real-space methods revealed three-core cluster units Ge16 Co3 and seemingly empty regions comprising either covalent inter-polyhedral Ge-Ge bonds or lone-pairs located at the germanium atoms. The electrical conductivity is metal-like.

Simultaneous Large Optical and Piezoelectric Effects Induced by Domain Reconfiguration Related to Ferroelectric Phase Transitions.

Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity, however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2 Nb1/2 )O3 -Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque polydomain structure into a highly transparent monodomain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm-1 ) and is accompanied by a large (>10 000 pm V-1 ) piezoelectric coefficient that is superior to linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices.

X-ray Diffraction, NMR Studies, and DFT Calculations of the Room and High Temperature Structures of Rubidium Cryolite, Rb3AlF6.

A crystallographic approach incorporating multinuclear high field solid state NMR (SSNMR), X-ray structure determinations, TEM observation, and density functional theory (DFT) was used to characterize two polymorphs of rubidium cryolite, Rb3AlF6. The room temperature phase was found to be ordered and crystallizes in the Fddd (no. 70) space group with a = 37.26491(1) Å, b = 12.45405(4) Å, and c = 17.68341(6) Å. Comparison of NMR measurements and computational results revealed the dynamic rotations of the AlF6 octahedra. Using in situ variable temperature MAS NMR measurements, the chemical exchange between rubidium sites was observed. The ß-phase, i.e., high temperature polymorph, adopts the ideal cubic double-perovskite structure, space group Fm3m, with a = 8.9930(2) Å at 600 °C. Additionally, a series of polymorphs of K3AlF6 has been further characterized by high field high temperature SSNMR and DFT computation.

Protein/Ice Interaction: High-Resolution Synchrotron X-ray Diffraction Differentiates Pharmaceutical Proteins from Lysozyme.

Protein/ice interactions are investigated by a novel method based on measuring the characteristic features of X-ray diffraction (XRD) patterns of hexagonal ice (Ih). Aqueous solutions of four proteins and other solutes are studied using high-resolution synchrotron XRD. Two pharmaceutical proteins, recombinant human albumin and monoclonal antibody (both at 100 mg/mL), have a pronounced effect on the properties of ice crystals, reducing the size of the Ih crystalline domains and increasing the microstrain. Lysozyme (100 mg/mL) and an antifreeze protein (1 mg/mL) have much weaker impact on Ih. Neither of the proteins studied exhibit preferred interactions with specific crystalline faces of Ih. It is proposed that the pharmaceutical proteins interact with ice crystals indirectly by accumulating in the quasi-liquid layer next to ice crystallization front, rather than directly, via a sorption on ice crystals. This is the first report, to the best of our knowledge, of major difference in the protein/ice interaction between non-antifreeze proteins. Another important finding is a detection of a second (minor) population of ice crystals, which is tentatively identified as a high-pressure form of ice, possibly IceIII or IceIX. This finding highlights a potential role of mechanical stresses in freeze-induced destabilization of proteins.

Erratum: Capecitabine from X-ray powder synchrotron data. Corrigendum.

[This corrects the article DOI: 10.1107/S1600536809017905.].

Ice Recrystallization in a Solution of a Cryoprotector and Its Inhibition by a Protein: Synchrotron X-Ray Diffraction Study.

Ice formation and recrystallization is a key phenomenon in freezing and freeze-drying of pharmaceuticals and biopharmaceuticals. In this investigation, high-resolution synchrotron X-ray diffraction is used to quantify the extent of disorder of ice crystals in binary aqueous solutions of a cryoprotectant (sorbitol) and a protein, bovine serum albumin. Ice crystals in more dilute (10 wt%) solutions have lower level of microstrain and larger crystal domain size than these in more concentrated (40 wt%) solutions. Warming the sorbitol-water mixtures from 100 to 228 K resulted in partial ice melting, with simultaneous reduction in the microstrain and increase in crystallite size, that is, recrystallization. In contrast to sorbitol solutions, ice crystals in the BSA solutions preserved both the microstrain and smaller crystallite size on partial melting, demonstrating that BSA inhibits ice recrystallization. The results are consistent with BSA partitioning into quasi-liquid layer on ice crystals but not with a direct protein-ice interaction and protein sorption on ice surface. The study shows for the first time that a common (i.e., not-antifreeze) protein can have a major impact on ice recrystallization and also presents synchrotron X-ray diffraction as a unique tool for quantification of crystallinity and disorder in frozen aqueous systems.

Unraveling the nature of electric field- and stress- induced structural transformations in soft PZT by a new powder poling technique.

A 'powder-poling' technique was developed to study electric field induced structural transformations in ferroelectrics exhibiting a morphotropic phase boundary (MPB). The technique was employed on soft PZT exhibiting a large longitudinal piezoelectric response (d(33) ∼ 650 pC N(-1)). It was found that electric poling brings about a considerable degree of irreversible tetragonal to monoclinic transformation. The same transformation was achieved after subjecting the specimen to mechanical stress, which suggests an equivalence of stress and electric field with regard to the structural mechanism in MPB compositions. The electric field induced structural transformation was also found to be accompanied by a decrease in the spatial coherence of polarization.

Capecitabine from X-ray powder synchrotron data.

In the title compound [systematic name 5-de-oxy-5-fluoro-N-(pent-yloxycarbon-yl)cytidine], C(15)H(22)FN(3)O(6), the pentyl chain is disordered over two positions with refined occupancies of 0.53 (5) and 0.47 (5). The furan ring assumes an envelope conformation. In the crystal, inter-molecular N-H⋯O hydrogen bonds link the mol-ecules into chains propagating along the b axis. The crystal packing exhibits electrostatic inter-actions between the 5-fluoro-pyrimidin-2(1H)-one fragments of neighbouring mol-ecules as indicated by short O⋯C [2.875 (3) and 2.961 (3) Å] and F⋯C [2.886 (3) Å] contacts.

Isosymmetrical phase transition in alpha-YbV4O8.

The structure of YbV4O8 is related to the CaFe2O4 structure type. VO6 octahedra form a three-dimensional framework with tunnels in which the Yb3+ ions are incorporated. Two different polymorphs alpha and beta are known and differ mainly in the arrangement of the Yb ions within the framework. We studied the structure and magnetic properties of alpha-YbV4O8 as a function of temperature. At approximately 70 K alpha-YbV4O8 undergoes a first-order isosymmetrical phase transition (P2(1)/n --> P2(1)/n). While in the high-temperature alpha phase the three V3+ and one V4+ are disordered over the four symmetrically independent octahedral sites, in the low-temperature alpha' phase complete charge ordering is observed. The transition is accompanied by a paramagnetic-paramagnetic anomaly in the magnetic susceptibility data which can be interpreted on the basis of spin-gap formation. The transition mechanism in the alpha polymorph is very similar to that observed earlier in the beta polymorph at 185 K.

Structure of compounds E(SnMe3)4 (E = Si, Ge) as seen by high-resolution X-ray powder diffraction and solid-state NMR.

The compounds tetrakis(trimethylstannyl)germane, Ge(SnMe3)4 (1), and tetrakis(trimethylstannyl)silane, Si(SnMe3)4 (2), have crystal structures with the quasispherical molecules in a closed-packed stacking. At room temperature both structures have the space group P1 (Z = 2) with a = 9.94457 (5), b = 14.52927 (8), c = 9.16021 (5) A, alpha = 90.53390 (30), beta = 111.73080 (30), gamma = 90.0049 (4) degrees, and V = 1229.414 (12) A3 for (1) and a = 9.92009 (7), b = 14.51029 (11), c = 9.13585 (7) A, alpha = 90.4769 (4), beta = 111.6724 (4), gamma = 89.9877 (6) degrees, and V = 1222.037 (16) A3 for (2). The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as shown by analyzing the distances between the atoms. Upon heating, both compounds undergo a first-order phase transition at temperatures T(c) = 348 +/- 5 K, as characterized by a relative jump of the lattice parameter of approximately 16%. At 353 K, both structures have the space group P1 (Z = 4), with a = 14.2037 (2) A, and V = 2865.52 (7) A3 for (1) and a = 14.1346 (2) A, and V = 2823.90 (7) A3 for (2). Rietveld refinements were performed for the low-temperature phases measured at T = 295 K [R(wp) = 0.0844 for (1), R(wp) = 0.0940 for (2)] and for the high-temperature phases measured at T = 353 K [R(wp) = 0.0891 for (1), R(wp) = 0.0542 for (2)]. The combination of high-resolution X-ray powder diffraction measurements and variable-temperature magic-angle-spinning 13C, 29Si and 119Sn NMR experiments demonstrates low crystallographic and molecular (C1) symmetries for the low-temperature phases of (1) and (2) at temperatures T < 348 +/- 5 K and high crystallographic symmetry due to rotational disorder for the high-temperature phases at temperatures T > 348 +/- 5 K.