Table of Contents

Abstract: A systematic investigation of phase transitions in unmilled and milled LiBH₄ has been performed by Pressurized Differential Scanning Calorimetry (PDSC). It was found that a large exotherm is present below the low temperature (LT) → high temperature (HT) phase transition. This exotherm is not caused by air contamination but seems to originate from hydrogen release from a solid solution in the matrix of LiBH₄ low temperature phase. The exotherm activation energy has been measured to be 100 kJ mol^–1. Calorimetric measurements under argon and hydrogen have shown that for the milled sample, the endothermic peak of the LT → HT transition is split in two when the PDSC scan is performed under hydrogen atmosphere. Synchrotron X-ray powder diffraction on the milled LiBH₄ sample revealed only a single-step transition from the LT to HT phase, both under vacuum and under 2 and 40 bar of hydrogen pressure. The axial ratios for the LT LiBH₄ below 300 K are significantly altered by milling; they are also considerably different under 40 bar of hydrogen, indicating an interaction between the hydrogen gas and the LT LiBH₄ solid phase.

Abstract: The possibility of substituting Pt/C with the hydrogen storage alloy MlNi_3.6Co_0.85Al_0.3Mn_0.3 as the anode active material of a proton exchange membrane fuel cell system has been analyzed. The electrochemical properties indicate that a much more electrochemically active anode is obtained by impregnating the active material loaded anode in a Nafion proton conducting polymer. Such performance improvement might result from the increase of three-phase boundary sites or length in the gas diffusion electrode where the electrochemical reaction occurs. The experimental data revealed that the membrane electrode assembly (MEA) shows better results when the anode active material, MlNi_3.6Co_0.85Al_0.3Mn_0.3, is treated with a hot alkaline KBH₄ solution, and then chemically coated with 3 wt.% Pd. The MEA with the aforesaid modification presents an enhanced surface capability for hydrogen adsorption, and has been studied by molecular beam-thermal desorption spectrometry.

Abstract: The title compound [H₂NNHC(NH₂)₂]₂[C₆HO₂(NO₂)₃] (2) was prepared in 85% yield by treatment of sodium styphnate with 2 equivalents of aminoguanidinium nitrate, followed by crystallization from aqueous solution. Compound 2 crystallizes in the triclinic space group Pī with unit cell dimensions a = 6.7224(3) Å, b = 10.7473(4) Å, c = 11.9604(5) Å, α = 113.212(4)°, β = 90.579(3)°, γ = 99.815(3)°, V = 779.68(6) ų, Z = 2. In the solid state structure of 2, no water of crystallization is present. Bond angles within the aromatic ring of the styphnate anion indicate a significant distortion with larger angles (122.04(18)–125.96(18) Å) at the carbons bearing the nitro groups, and smaller ones (113.30(17) and 114.07(17) Å) at the C-O⁻ carbon atoms. The crystal structure of 2 consists of layers formed by an extensive network of N-H^...O hydrogen bonds between NH₂ groups of the aminoguanidinium cation and the negatively charged oxygens of the styphnate anion. The layers are again interconnected by N-H^...N hydrogen bonds between neighboring aminoguanidinium cations.

Abstract: New radical cation salts (BEDT-TTF)[8,8',(7)-Cl₂(Cl_0.09)-3,3'-Co(1,2-C₂B₉H_9.91)(1',2'-C₂B₉H₁₀)] (1), (BEDT-TTF)[8,8'-Br_0.75Cl_1.25-3,3'-Co(1,2-C₂B₉H₁₀)₂] (2), and (BMDT-TTF)₄[8,8'-Br_1.16(OH)_0.72-3,3'-Co(1,2-C₂B₉H_10.06)₂] (3) were synthesized, and their crystal structures and electrical conductivities were determined. All the radical cation salts are semiconductors. Compounds 1 and 2 were found to be isostructural, however their electrical conductivities strongly differ (s₂₉₃ = 2 Ω⁻¹cm⁻¹ and 10⁻⁵ Ω⁻¹cm⁻¹, respectively).

Abstract: Dynamics of photoinduced phase transitions in molecular conductors are reviewed from the perspective of interplay between correlated electrons and phonons. (1) The charge-transfer complex TTF-CA shows a transition from a neutral paraelectric phase to an ionic ferroelectric phase. Lattice phonons promote this photoinduced transition by preparing short-range lattice dimerization as a precursor. Molecular vibrations stabilize the neutral phase so that the ionic phase, when realized, possesses a large ionicity and the Mott character; (2) The organic salts θ-(BEDT-TTF)₂RbZn(SCN)₄ and α-(BEDT-TTF)2I3 show transitions from a charge-ordered insulator to a metal. Lattice phonons make this photoinduced transition hard for the former salt only. Molecular vibrations interfere with intermolecular transfers of correlated electrons at an early stage; (3) The organic salt κ-(d-BEDT-TTF)₂Cu[N(CN)₂]Br shows a transition from a Mott insulator to a metal. Lattice phonons modulating intradimer transfer integrals enable photoexcitation-energy-dependent transition pathways through weakening of effective interaction and through introduction of carriers.

Abstract: This article investigates hole transport in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV)/CdSe colloidal quantum dot (CQD) nanocomposites using a modified time-of-flight photoconductivity technique. The measured hole drift mobilities are analyzed in the context of Bässler’s Gaussian disorder model and the correlated disorder model in order to determine the polymer internal morphology of hybrid nanocomposite thin films. This work shows that increasing the CdSe CQD concentration decreases the polymer hole mobility from ~5.9 × 10⁻⁶ cm²/Vs in an MEH-PPV film to ~8.1 × 10⁻⁸ cm²/Vs in a 20:80 (wt%) MEH-PPV:CdSe CQD nanocomposite film (measured at 25 °C and ~2 × 10⁵ V/cm). The corresponding disorder parameters indicate increasing disruption of interchain interaction with increasing CQD concentration. This work quantifies polymer chain morphology in hybrid nanocomposite thin films and provides useful information regarding the optimal use of semiconductor nanocrystals in conjugated polymer-based optoelectronics.

Abstract: The crystal and molecular structure of tert-butyl 4-(2-tert-butoxy-2-oxoethyl)-piperazine-1-carboxylate is reported. The title compound crystallizes from a petroleum ether/ethyl acetate mixture in the monoclinic space group P 2₁/c with four molecules in the unit cell. The unit cell parameters are: a = 8.4007(2) Å, b = 16.4716(4) Å, c = 12.4876(3) Å; β = 90.948(1)° and V = 1727.71(7) ų. Bond lengths and angles of this piperazine-carboxylate are typical.

Abstract: The crystal structures of four salts of 1,4-diazabicyclo[2.2.2]octane (DABCO) and 5-aminotetrazole are described. Anhydrous 1:1 (Pbca, R_gt = 0.041) and 1:2 (P, R_gt = 0.038) salts form hydrogen-bonded layers of anions and cations. The monohydrate of the 1:1 compound (P2₁/c, R_gt = 0.038) shows infinite chains of DABCO cations and an undulated layer of anions and water molecules. The octahydrate of the 3:2 compound (P2₁/c, R_gt = 0.042) features DABCO triples and clusters of four tetrazolate ions in a network of water molecules.

Abstract: The crystal and molecular structure of 1,2:5,6-di-O-isopropylidene-3-O-toluenesulfonyl-α-D-glucofuranose is reported. This compound crystallizes from a petroleum ether/ethyl acetate mixture with the chiral orthorhombic space group P2₁2₁2₁ with four molecules in the unit cell. The unit cell parameters are: a = 9.7945(7) Å, b = 10.1945(7) Å, c = 21.306(1) Å, and V = 2127.4(2) ų. No classical hydrogen bonds were found. Bond lengths and angles of this tosylated glucofuranose derivative are typical.

Abstract: The first betaine chloride tetrachloroidoferrate(III) double salt, (Hbet)₂Cl[FeCl₄] = (Hbet)Cl·(Hbet)[FeCl₄], was obtained from a solution of betaine hydrochloride (HbetCl) and FeCl₃∙6 H₂O in water. The crystal structure (orthorhombic, Pbcm, a = 6.2717(13), b = 12.841(3), c = 25.693(5) Å, Z = 4) is characterized by layers of tetrachloridoferrate(III) anions separated by chloride-bridged, H-bond mediated cationic (Hbet) dimers. The hydrogen bonding network in the crystal structure follows the Pearson HSAB (hard acid-soft base) concept: According to the Pearson concept, the chloride anions show high affinity to the carboxyl group (hard acid and base), and the tetrachloroidoferrate(III) anion preferentially interacts with the activated methyl donors (soft acid and base). These interactions between the COOH group, as hard H-bond donor, and chloride as hard acceptor besides those between the soft, activated methyl groups and the soft tetrachloridoferrate(III) anions are the major structure-directing forces in the crystal structure of (Hbet)₂Cl[FeCl₄].

Abstract: Crystalline 2-ethylimidazole-1-sulfonyl azide was designed as a convenient reagent with improved thermal stability for electrophilic azidation of carbanions. The compound crystallized in the monoclinic space group P2₁/c. The molecules are arranged into chains by short C–H...O contacts along a two-fold screw axis. The quaternary 1-azidosulfonyl-2-ethyl-3-methylimidazolium tetrafluoroborate crystallized in Fdd2 with two independent ion pairs which engage in C–H...F interactions.

Abstract: Five new 5,5'-azotetrazolate salts (amminsilver, trimethylsulfonium, tetramethyl-phosphonium, trimethylsulfoxonium, 2-(hydroxyethyl)trimethylammonium) were prepared and characterized. The crystal structures were determined by X-ray diffraction. Interactions between the ions are identified and discussed. The sensitivities of the highly energetic silver salt were measured by BAM (Bundesanstalt für Materialforschung und-prüfung) methods.

Abstract: The title compound (3) was prepared from 4-chloroaniline in good yield on successive oxidation and methylation and its crystal and molecular structure is reported. The compound crystallizes in the monoclinic space group P 2₁/n with unit cell dimensions a = 13.5698(8), b = 3.7195 (3), c = 13.5967 (8) Å, ß = 91.703(3) °, V = 685.96 (10) ų. The molecule is essentially planar with a dihedral angle of 6.2(3) ° between the nitro group and the phenyl ring. The crystal structure is stabilised by π...π contacts between adjacent benzene rings together with C–H...O hydrogen bonds and close Cl...O contacts.

Abstract: Anion substitution is at present one of the pathways to destabilize metal borohydrides for solid state hydrogen storage. In this work, a solid solution of LiBH₄ and LiCl is studied by density functional theory (DFT) calculations, thermodynamic modeling, X-ray diffraction, and infrared spectroscopy. It is shown that Cl substitution has minor effects on thermodynamic stability of either the orthorhombic or the hexagonal phase of LiBH₄. The transformation into the orthorhombic phase in LiBH₄ shortly after annealing with LiCl is for the first time followed by infrared measurements. Our findings are in a good agreement with an experimental study of the LiBH₄-LiCl solid solution structure and dynamics. This demonstrates the validity of the adopted combined theoretical (DFT calculations) and experimental (vibrational spectroscopy) approach, to investigate the solid solution formation of complex hydrides.