Yu-Sheng Chen

Chemical bonding and intermolecular interactions in energetic materials: 1,3,4-trinitro-7,8-diazapentalene

The electron density and related properties of the red-colored energetic material 1,3,4-trinitro-7,8-diazapentalene (space group Pca2(1)) have been determined from a low-temperature [90.0 (1) K] X-ray diffraction experiment. Intensity data were measured with a 2 K CCD Bruker diffractometer using Ag Kalpha radiation. One detector setting, several varphi settings, 0.15 degrees omega scans and 96 s exposure time per frame gave R(int) = 0.0188 for 31 952 (10 283 unique) reflections and (sin theta/lambda)(max) = 1.15 A(-1). The electron density was modeled using the Hansen-Coppens [(1978), Acta Cryst. A34, 909-921] multipole model and refined to R = 0.026 for 9455 unique observed reflections. The electron density, Laplacian and electrostatic potential distributions are reported and discussed. The properties of the bond (3,-1) critical points are analyzed. All results are indicative of multiple bonds in the five-membered rings. In addition, a significant number of weak intermolecular interactions (O...H, O...O, O...N, O...C) have also been characterized by the properties of their critical points. A comparison of experimental results with those obtained from theoretical calculations (periodic, CRYSTAL98; single molecule, GAUSSIAN98) is also reported.

Cryogenic (<20 K) helium cooling mitigates radiation damage to protein crystals

In experiments conducted at the Bio-CARS beamline 14-BM-C (APS, Argonne National Laboratory, USA), Streptomyces rubiginosus D-xylose isomerase (EC 5.3.1.5) crystals were used to test the effect of cryogen temperature on radiation damage. Crystals cooled using a helium cryostat at an 8 K set temperature consistently showed less decay in the signal-to-noise ratio, I/sigma(I), and in average intensity, I, compared with those cooled with a nitrogen cryostat set to 100 K. Multiple crystals grown using ammonium sulfate as precipitant were used at each cryostat set temperature and comparisons were made for crystals of similar size and diffraction resolution. Maximum resolution for the crystals was 1.1-1.3 A, with He at <20 K extending the lifetime of the high-resolution data by >25% compared with crystals cooled with N(2) at 100 K.

Accurate charge density data collection in under a day with a home X-ray source

Accurate charge density data for pentaerythritol were measured at 15 K in the laboratory in under a day using a Rigaku R-Axis Rapid high-power rotating-anode diffractometer with a curved image-plate detector, and open-flow liquid-helium cryostat. The experimental procedure and data treatment are briefly described, and data quality evaluated based on a number of criteria.

Pressure versus Temperature Effects on Intramolecular Electron Transfer in Mixed‐Valence Complexes

Mixed-valence trinuclear carboxylates, [M(3)O(O(2)CR)(6)L(3)] (M = metal, L = terminal ligand), have small differences in potential energy between the configurations M(II)M(III)M(III)⇔M(III)M(II)M(III)⇔M(III)M(III)M(II), which means that small external changes can have large structural effects, owing to the differences in coordination geometry between M(2+) and M(3+) sites (e.g., about 0.2u2005Å for Fe-O bond lengths). It is well-established that the electron transfer (ET) between the metal sites in these mixed-valence molecules is strongly dependent on temperature and on the specific crystal environment; however, herein, for the first time, we examine the effect of pressure on the electron transfer. Based on single-crystal X-ray diffraction data that were measured at 15, 90, 100, 110, 130, 160, and 298u2005K on three different crystals, we first unexpectedly found that our batch of Fe(3)O (O(2)CC(CH(3))(3))(6)(C(5)H(5)N)(3) (1) exhibited a different temperature dependence of the ET process than previous studies of compound 1 have shown. We observed a phase transition at around 130u2005K that was related to complete valence trapping and Hirshfeld surface analysis revealed that this phase transition was governed by a subtle competition between C-H⋅⋅⋅π and π⋅⋅⋅π intermolecular interactions. Subsequent high-pressure single-crystal X-ray diffraction at pressures of 0.15, 0.35, 0.45, 0.74, and 0.96u2005GPa revealed that it was not possible to trigger the phase transition (i.e., valence trapping) by a reduction of the unit-cell volume, owing to this external pressure. We conclude that modulation of the ET process requires anisotropic changes in the intermolecular interactions, which occur when various directional chemical bonds are affected differently by changes in temperature, but not by the application of pressure.

Re-investigation of the structure and crystal chemistry of the Bi2O3-W2O6 'type (Ib)' solid solution using single-crystal neutron and synchrotron X-ray diffraction.

Single crystals of composition Bi(35.66)W(4.34)O(66.51) (or Bi(8.2)WO(15.3), bismuth tungsten oxide), within the type (Ib) solid-solution region of the Bi(2)O(3)-WO(3) system, were synthesized using the floating-zone furnace method. Synchrotron X-ray and neutron single-crystal diffraction data were used to confirm the previously tentative assignment of the room-temperature space group as I4(1). Fourier analysis of the combined X-ray and neutron datasets was used to elucidate and refine fully the cation and anion arrays for the first time. The mixed cation site M1 is shown to be coordinated by eight O atoms in an irregular cube when M = Bi, and by six O atoms in an octahedron when M = W. The resulting disorder in the average structure around M1 is discussed in the context of experimentally observed oxide-ion conductivity.

Electron density, electrostatic potential, and spatial organization of ammonium hydrooxalate oxalic acid dihydrate heteromolecular crystal from data of diffraction experiment at 15 K using synchrotron radiation and theoretical calculations

A high-precision diffraction study at 15 K using synchrotron radiation and theoretical calculation of a heteromolecular crystal ammonium hydrooxalate oxalic acid dihydrate NH4+·C2HO4−·C2H2O4·2H2O (1) were carried out. The calculation was performed with the Kohn-Sham method taking into account periodic boundary conditions. The joint experimental and theoretical study allowed one to locate positions of hydrogen atoms and to reliably establish peculiar features of the electron density and electrostatic potential distributions in 1. Interatomic and molecular interactions were characterized based on the electron density properties within the framework of a quantum topological theory. The bond order indices were calculated from the experimental electron density without using the orbital notions. A new approach based on visualization of the ellipsoids whose semiaxes depend on the principal values of the electron density curvature at the bond critical points was used. It was found that charge transfer between ammonium cation and hydrooxalate anion in 1 dominates other electrostatic interactions in the crystal. Based on analysis of peculiar features of the electron density and electrostatic potential distributions in the crystal of 1, it was found that spatial organization of the crystal in hand is also governed by one more, weaker, electrostatic factor that originated from the presence of well-localized regions behind protons on the extensions of the lines of covalent bonds at the periphery of the molecules. In those regions, the electrostatic potential is higher than in other directions due to anisotropy of the electron density distribution. This feature mainly ensures directed complementary electrostatic interaction between corresponding fragments with negatively charged regions of neighboring molecules, such as the lone electron pairs and p-electrons.

Nontypical iodine-halogen bonds in the crystal structure of (3E)-8-chloro-3-iodomethylidene-2,3-dihydro-1,4-oxazino[2,3,4-ij]quinolin-4-ium triiodide.

Two kinds of iodine-iodine halogen bonds are the focus of our attention in the crystal structure of the title salt, C12H8ClINO(+)·I3(-), described by X-ray diffraction. The first kind is a halogen bond, reinforced by charges, between the I atom of the heterocyclic cation and the triiodide anion. The second kind is the rare case of a halogen bond between the terminal atoms of neighbouring triiodide anions. The influence of relatively weakly bound iodine inside an asymmetric triiodide anion on the thermal and Raman spectroscopic properties has been demonstrated.

Study of acid pyridine-3-carboxylic acid dodecatungstenphosphate of the composition (C6NO2H5)2H[PW12O40]·2H2O

Acid pyridine-3-carboxylic acid dodecatungstenphosphate (C6NO2H5)2H[PW12O40]·2H2O is synthesized. The compound is studied by chemical analysis, IR spectroscopy, X-ray crystallography, and thermogravimetry. The compound is found to crystallize at 290 K in a hexagonal crystal system (space group

High-Pressure Crystal Structures of an Insensitive Energetic Crystal: 1,1-Diamino-2,2-dinitroethene

Rbar 3