Quasi-two-dimensional organic metals with differently oriented conducting layers

New layered organic conductors based on selenium- and sulfur-containing donor molecules of bis(ethylenedithio)tetraselenafulvalene (BETS) and deuterated bis(ethylenedithio)-tetrathiafulvalene (ET) with tetrahedral anions of divalent metals of the general formula (BETS)₄HgBr₄(1,2-C₆H₄Cl₂), (ET-d₈)₄HgBr₄(C₆H₄Cl₂) and (ET-d₈)₄HgBr₄(C₆H₅X) (where X = Cl, Br) were synthesized using halobenzenes as solvents. The crystal structure of (BETS)₄HgBr₄(C₆H₄Cl₂) was studied at room temperature. A distinctive feature of the crystal structures of the compounds is the alternation of the conducting layers, which differ in direction of the radical cation stacks. The conductivity along the layers is of metallic character with the temperature decrease down to 4.3 K for (BETS)₄HgBr₄(C₆H₄Cl₂) and down to 40—105 K for ET-d₈-based compounds, while in the direction perpendicular to the conducting layers the conductivity is semiconducting. A comparative analysis of the temperature dependence of the resistivity for the compounds (ET)₄HgBr₄(Solvent) (Solvent is 1,2-C₆H₄Cl₂, C₆H₅X), which are based on ET and its deuterated analog, allows one to suggest that the metal—metal phase transitions observed in the 220—285 K range are of different origin: in the compounds containing 1,2-C₆H₄Cl₂ they are due to the ordering of solvent molecules, whereas in the compounds containing C₆H₅X the transitions are associated with rearrangements of the terminal ethylene groups.     

Synthesis and structure of 7<Emphasis Type="Italic">H</Emphasis>-12-Oxa-3,7-diazapleiadenes

The molecular structures of 9,11-di-tert-butyl-2,4-dimethyl-7H-12-oxa-3,7-diazapleiadene and 7-acetyl-9,11-di-tert-butyl-2,4,6-trimethyl-7H-12-oxa-3,7-diazapleiadene were determined by X-ray analysis.     

Synthesis and structure of asymmetric 2,4,6-triazidopyridines

The reactions of 3-cyanotetrafluoropyridine and tetrachloro-3-trifluoromethylpyridine with sodium azide lead to the corresponding 2,4,6-triazido-5-cyano-3-fluoropyridine and 2,4,6-triazido-5-chloro-3-trifluoromethylpyridine. With the aid of comparative X-ray structural analysis of 2,4,6-triazido-5-cyano-3-fluoropyridine and its previously known 3-chloro-substituted derivative it was established that the geometric parameters and reactivity of the azide groups in the asymmetric 2,4,6-triazi-dopyridines depend not only on the position of these groups in the pyridine ring but also on their mutual orientation in space.     

C(2)-Functionalization of 1-substituted imidazoles with cyanoacetylenes and aromatic or heteroaromatic aldehydes

Substituted imidazoles (substituents are Me, Et, i-Bu, n-Hexyl, (CH₂)₂S-Bu-n, Ph, Bn) react smoothly (room temperature, without catalyst and solvent) with cyanoacetylenes (3-phenyl-2-propynenitrile and 4-(1-butoxyethoxy)-4-methyl-2-pentynenitrile) and aromatic or heteroaromatic aldehydes (benzaldehyde, 4-CN-benzaldehyde, pyridine-3-aldehyde) to give 3-(2-imidazolyl)-3-aryl-2-acylpropanenitriles, a hitherto unknown family of functionalized imidazole derivatives, in up to 62% yield. This three-component manifold represents a novel C(2)-functionalization of the imidazole nucleus involving zwitterionic, carbene and enol ether intermediates. Unlike the analogous reaction with aliphatic aldehydes, which gives enol ethers, in this case the latter undergo the further rearrangement to 3-(2-imidazolyl)-3-aryl-2-acylpropanenitriles.     

Concerted reactions of polynuclear metalloenzymes and their functional chemical models

The mechanisms of the many-electron oxidation of water by a chemical model of the manganese oxidase cofactor in photosynthesis photosystem II (manganese(IV) clusters) and nitrogen reduction in chemical models of nitrogenase cofactor (vanadium(II) and molybdenum(III) clusters) were considered. The hypothesis was suggested according to which polynuclear enzyme cofactors and their functional chemical models performed two important functions, catalyzed noncomplementary processes and effected many-substrate concerted reactions with decreased activation energies.     

Dynamics of optical response of solutions of pseudoisocyanine <Emphasis Type="Italic">J</Emphasis> aggregates upon pico- and subnanosecond excitation

The luminescence kinetics of solutions of pseudoisocyanine iodide (PIC) J aggregates is studied upon excitation by pico- and subnanosecond laser pulses into the main superintense long-wavelength absorption band. The dependences of the transmission and luminescence energy on the pump energy are measured. It is found that the shape of the luminescence kinetics depends on the recording and excitation spectral regions, which is obviously related to the energy transfer between coherently coupled fragments of J aggregates.     

Structure and mobility in ferroelectric liquid crystalline elastomers

Time-resolved Fourier transform infrared (FTIR) spectroscopy with polarized light was employed to study the structure and mobility of a homologous series of ferroelectric liquid crystalline polymers (FLCPs) and ferroelectric liquid crystalline elastomers (FLCEs) in response to an external electric field. The chemical composition of the samples, besides the cross-linking units, is similar. For the elastomers, two different cross-linking architectures are realized: “intralayer” cross-linking leads to the formation of two-dimensional networks, whereas “interlayer” cross-linking forms three-dimensional networks. Due to its specificity, FTIR spectroscopy enables analysis of the reorientational dynamics for the different molecular moieties in detail, thus revealing information about reorientation times, angular excursion, and the phase relationship in the rearrangement of the various molecular groups. In comparison to the un-cross-linked FLCP, both elastomeric samples exhibited smaller reorientation angles and an increase of the reorientation times. In the case of the interlayer cross-linked FLCE, an elastic memory effect was observed: For the reversal from negative to positive field polarity, the reorientation times were longer than for those in the opposite direction. For the intralayer cross-linked sample, it was shown that the backbone molecules reorient slower than the other molecular units (“locomotive effect”). For the un-cross-linked FLCP and the two FLCE samples, different coupling mechanisms between the network and the mesogenic parts are derived from the measurements.     

The parametric doppler effect upon oblique radiation incidence in quartz glass

Frequency and reflection angle of probe radiation from a refractive-index inhomogeneity induced by an intense pumping pulse in quartz glass and moving with a relativistic velocity are calculated. Conditions under which the normal component of the wave vector of the reflected wave is directed to the opposite or to the same direction as the same component for the incident wave are determined. Comparison with the case of radiation reflection from a relativistic mirror in vacuum is performed. Conditions of the appearance of the Vavilov-Cherenkov radiation from a relativistic refractive-index inhomogeneity induced in the medium by an intense laser pulse are discussed.