Crystals, Volume 2, Issue 4 (December 2012) – 12 articles , Pages 1366-1513

The metallic state of the molecular conductor β-(meso-DMBEDT-TTF)₂X (DMBEDT-TTF = 2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-ylidene)-5,6-dihydro-5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin, X = PF₆, AsF₆) is transformed into the checkerboard-type charge-ordered state at around 75–80 K with accompanying metal-insulator (MI) transition on the anisotropic triangular lattice. With lowering temperatures, the magnetic susceptibility decreases gradually and reveals a sudden drop at the MI transition. By applying pressure, the charge-ordered state is suppressed and superconductivity appears in β-(meso-DMBEDT-TTF)₂AsF₆ as well as in the reported β-(meso-DMBEDT-TTF)₂PF₆. The charge-ordered spin-gapped state and the pressure-induced superconducting state are discussed through the paired-electron crystal (PEC) model, where the spin-bonded electron pairs stay and become mobile in the crystal, namely the valence-bond solid (VBS) and the resonant valence bonded (RVB) state in the quarter-filled band structure. Full article

The crystal structures of 1-hydroxyimidazole and four protic salts (chloride, bromide, sulfate, nitrate) thereof were determined. The molecular geometries (bond lengths and angles) of the free base and the salts were compared. Hydrogen bonding patterns were studied, and OH…N, OH…Cl, OH…Br, OH…O, NH…Cl, NH…Br, and NH…O interactions were identified. Hirshfeld surface analysis gave quantitative insight into these interactions. Full article

The photonic bands of various TiO₂ 2D photonic crystals, i.e., cylindrical, square and hexagonal columns connected with/without walls and filled with acetonitrile, were investigated from the perspective of dye-sensitized solar cells. The finite-difference time-domain methods revealed that two-dimensional (2D) photonic crystals with rods connected with walls composed of TiO₂ and electrolytes had complete photonic band gaps under specific conditions. This optimally designed bandgap reaches a large Δω/ω_mid value, 1.9%, in a triangular array of square rods connected with walls, which is the largest complete 2D bandgap thus far reported for a photochemical system. These discoveries would promote the photochemical applications of photonic crystals. Full article

An improved synthesis of the Cholesteryl Ester Transfer Protein inhibitor dalcetrapib is reported. The precursor disulfide was reduced (a) by Mg/MeOH or (b) by EtSH/DBU/THF. The resulting thiol was acylated (a) by a known procedure or (b) in a one-pot process. Impurities were removed (a) by dithiothreitol (DTT) or (b) by oxidation using H₂O₂. Dalcetrapib crystallized in space group P2₁/c. Full article

The absolute configuration and structure of aegelinol, a pyranocoumarin isolated from Ferulago asparagifolia Boiss (Apiaceae), has been determined by crystallography. Crystal structure of the inclusion complex of aegelinol in β-cyclodextrin was determined (a = 15.404(1) Å, b = 15.281(1) Å, c = 17.890(1) Å, α = 99.662(1), β = 113.4230(1), γ = 102.481(1)°, P1; R₁ = 6.71%) and allowed unambiguous determination of the absolute configuration of the stereogenic center of aegelinol. The pyranocoumarin guest is included within the cylindrical cavity formed by dimeric β-cyclodextrin molecules with a head-to-head arrangement. Crystal structure of aegelinol alone was also determined (a = 6.8921(3) Å, b = 11.4302(9) Å, c = 44.964(3) Å, P2₁2₁2₁; R₁ = 4.44%) and allowed precise determination of its geometry. Aegelinol crystallizes with three molecules in the asymmetric unit held together by H-bonds and π-stacking interactions. Full article

Piperidinium copper(I) bromide, (C₅H₁₂N)Cu₂Br₃, was obtained from a solution of CuBr₂, piperidine, and HBr in ethanol. At 60 °C ethanol slowly reduces copper(II) to copper(I). Colorless plates of (C₅H₁₂N)Cu₂Br₃ crystallize in the triclinic space group P-1 with lattice parameters of a = 6.2948(10) Å, b = 8.2624(14) Å, c = 10.7612(17) Å, α = 75.964(19)°, β = 89.232(19)°, γ = 84.072(19)°, and Z = 2 at 173 K. [CuBr₄] tetrahedra share edges and form [Cu₂Br₃]⁻ ladders parallel to the a-axis. (C₅H₁₂N)⁺ ions adopt a chair conformation and connect the [Cu₂Br₃]⁻ ladders via H-bonding. The (C₅H₁₂N)Cu₂Br₃ structure is related to the mineral rasvumite, KFe₂S₃, space group Cmcm, which is isostructural to several alkali copper(I) halides. Full article

As potential hydrogen storage media, magnesium based hydrides have been systematically studied in order to improve reversibility, storage capacity, kinetics and thermodynamics. The present article deals with the electrochemical and optical properties of Mg alloy hydrides. Electrochemical hydrogenation, compared to conventional gas phase hydrogen loading, provides precise control with only moderate reaction conditions. Interestingly, the alloy composition determines the crystallographic nature of the metal-hydride: a structural change is induced from rutile to fluorite at 80 at.% of Mg in Mg-TM alloy, with ensuing improved hydrogen mobility and storage capacity. So far, 6 wt.% (equivalent to 1600 mAh/g) of reversibly stored hydrogen in Mg_yTM_(1-y)H_x (TM: Sc, Ti) has been reported. Thin film forms of these metal-hydrides reveal interesting electrochromic properties as a function of hydrogen content. Optical switching occurs during (de)hydrogenation between the reflective metal and the transparent metal hydride states. The chronological sequence of the optical improvements in optically active metal hydrides starts with the rare earth systems (YH_x), followed by Mg rare earth alloy hydrides (Mg_yGd_(1-y)H_x) and concludes with Mg transition metal hydrides (Mg_yTM_(1-y)H_x). In-situ optical characterization of gradient thin films during (de)hydrogenation, denoted as hydrogenography, enables the monitoring of alloy composition gradients simultaneously. Full article

Properties of strontium tetraborate (SBO) and features of as-grown anti-parallel domains are summarized. From the point of view of nonlinear optics, these domains form nonlinear photonic crystals (NPC). Applications of NPC to the deep ultraviolet generation and fs pulse diagnostics are described. NPC and SBO are prospective media for the creation of a widely tunable source of fs pulses in the vacuum ultraviolet and for autocorrelation diagnostics of broadly tunable sources. Full article

We examined optical fibers suitable for avoiding such problems as the fiber fuse phenomenon and failures at bends with a high power input. We found that the threshold power for fiber fuse propagation in photonic crystal fiber (PCF) and hole-assisted fiber (HAF) can exceed 18 W, which is more than 10 times that in conventional single-mode fiber (SMF). We considered this high threshold power in PCF and HAF to be caused by a jet of high temperature fluid penetrating the air holes. We showed examples of two kinds of failures at bends in conventional SMF when the input power was 9 W. We also observed the generation of a fiber fuse under a condition that caused a bend-loss induced failure. We showed that one solution for the failures at bends is to use optical fibers with a low bending loss such as PCF and HAF. Therefore, we consider PCF and HAF to be attractive solutions to the problems of the fiber fuse phenomenon and failures at bends with a high power input. Full article

The three dimensional bismuth ethanedisulfonate framework Bi(O₃SC₂H₄SO₃)_1.5(H₂O)₂ was synthesized under hydrothermal conditions using the bidentate ligand 1,2-ethanedisulfonate and then characterized through X-ray diffraction and elemental analyses. The bismuth cation coordinates at three different ethanedisulfonate ligands and has a coordination number of eight, which is accompanied by a distorted square antiprismatic configuration. Here, we report on the crystal structure of this bismuth metal–organic framework and its coordination behavior, which has thus far not been reported in heavier main group elements. Full article

The synthesis and crystal structure of the one-dimensional coordination polymer, [Cd(spar)₂]_n·n(H₂O), are described, where spar⁻ is the sparfloxacinate anion, C₁₉H₂₁N₄O₃F₂⁻. The Cd²⁺ ion is bonded to four spar⁻ ligands: Two O,O-chelate with their β-keto carboxylate groupings and two are monodentate-bound through a carboxylate O atom, to result in a distorted CdO₆ octahedral coordination geometry. The bridging ligands lead to [100] polymeric chains in the crystal and N–H···O hydrogen bonds and possible weak aromatic p–p stacking interactions help to consolidate the structure. Crystal data: C₃₈H₄₄CdF₄N₈O₇, M_r = 913.21, triclinic, (No. 2), Z = 2, a = 9.2256(4) Å, b = 12.8767(5) Å, c = 17.4297(7) Å, α = 89.505(2)°, β = 85.062(2)°, g = 70.757(2)°, V = 1947.20(14) ų, R(F) = 0.036, wR(F²) = 0.082. Full article