Gerhard Laus , Volker Kahlenberg , Klaus Wurst , Michael Hummel and Herwig Schottenberger
Article: 1,4-Diazabicyclo[2.2.2]octane (DABCO) 5-aminotetrazolates
Crystals 2012, 2(1), 96-104; doi:10.3390/cryst2010096 - published online 6 February 2012
Show/Hide AbstractAbstract: 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.

Constantin Mamat , Anke Flemming and Martin Köckerling
Communication: Synthesis and Molecular Structure of tert-Butyl 4-(2-tert-butoxy-2-oxoethyl)piperazine-1-carboxylate
Crystals 2012, 2(1), 90-95; doi:10.3390/cryst2010090 - published online 6 February 2012
Show/Hide AbstractAbstract: 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.

Ryan Pate and Adrienne D. Stiff-Roberts
Article: Influence of Semiconductor Nanocrystal Concentration on Polymer Hole Transport in Hybrid Nanocomposites
Crystals 2012, 2(1), 78-89; doi:10.3390/cryst2010078 - published online 16 January 2012
Show/Hide AbstractAbstract: 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.

Kenji Yonemitsu
Review: Theory of Photoinduced Phase Transitions in Molecular Conductors: Interplay Between Correlated Electrons, Lattice Phonons and Molecular Vibrations
Crystals 2012, 2(1), 56-77; doi:10.3390/cryst2010056 - published online 6 January 2012
Show/Hide AbstractAbstract: 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.

Olga N. Kazheva , Grigory G. Aleksandrov , Andrey V. Kravchenko , Vladimir A. Starodub , Irina A. Lobanova , Irina D. Kosenko , Igor B. Sivaev , Vladimir I. Bregadze , Lev I. Buravov and Oleg A. Dyachenko
Article: New Fulvalenium Salts of Cobalt Bis(dicarbollide): Crystal Structures and Electrical Conductivities
Crystals 2012, 2(1), 43-55; doi:10.3390/cryst2010043 - published online 6 January 2012
Show/Hide AbstractAbstract: 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).

Raik Deblitz , Cristian G. Hrib , Georg Plenikowski and Frank T. Edelmann
Article: Molecular and Crystal Structure of a New High Energy Density Material: Aminoguanidinium-styphnate, [H₂NNHC(NH₂)₂]₂[C₆HO₂(NO₂)₃]
Crystals 2012, 2(1), 34-42; doi:10.3390/cryst2010034 - published online 4 January 2012
Show/Hide AbstractAbstract: 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.