Conductor chiral

Keywords Conductors Chiral induction Gels Liquid crystals Magnetism Abbreviations... 

These considerations, thus, lay the groundwork for tests among several semi-empirical approaches to the estimation of optical rotation of bond systems regarded as helices. Should it be necessary to use Eq. (lb) rather than (la), then a sweeping reassessment of the use of the helical conductor model will be required. However that test turns out, a test between that model and the simple conformational dissymmetry model becomes possible on the basis of the material shown in Table 1. At this point it should be said that our calculations on twistane 16> support the helical conductor model but that the results obtained by Pino and his co-workers 17 18> on the chiroptical properties of isotactic polymers prepared from chiral a-olefins support the conformational dissymmetry model. [We are not able, at present anyhow, to account for their results with the helical conductor model]. 

One approach to chiral conductors using the counterions as the source of asymmetry is that employed in the preparation of a conductor based on bis(ethylenedithio)-tetrathiafulvalene (BEDT, Fig. 3) [39]. When this organic donor is electrocrystallised in the presence of the L-tartrate salt K2[Sb2 (L-tart)2] the compound that is formed is BEDT3Sb2(L-tart)2 MeCN. Thus, the BEDT is in a mixed valence state, with two third charge per molecule on average. The salt, which pertains to the P2i2i2i space group, has layers of donor molecules and ions derived from BEDT which alternate with layers of the chiral counter-ions. 

The preparation of chiral conductors is perhaps most easily achieved by supramolecular induction in preformed achiral conducting polymers. Al-... 

As mentioned above, electronic properties of CNTs depend on the chirality and presence of defects in the scrolled graphene layer. Metallic nanotubes can have an electric current density more than 1,000 times greater than metals such as silver and copper. All nanotubes are expected to be very good thermal conductors along the tube, but good insulators laterally to the tube axis.8... 

Although many satisfactory VCD studies based on the gas phase simulations have been reported, it may be necessary to account for solvent effects in order to achieve conclusive AC assignments. Currently, there are two approaches to take solvent effects into account. One of them is the implicit solvent model, which treats a solvent as a continuum dielectric environment and does not consider the explicit intermolecular interactions between chiral solute and solvent molecules. The two most used computational methods for the implicit solvent model are the polarizable continuum model (PCM) [93-95] and the conductor-like screening model (COSMO) [96, 97]. In this treatment, geometry optimizations and harmonic frequency calculations are repeated with the inclusion of PCM or COSMO for all the conformers found. Changes in the conformational structures, the relative energies of conformers, and the harmonic frequencies, as well as in the VA and VCD intensities have been reported with the inclusion of the implicit solvent model. The second approach is called the explicit solvent model, which takes the explicit intermolecular interactions into account. The applications of these two approaches, in particular the latter one will be further discussed in Sect. 4.2. 

Chirality is a very general symmetry concept, and its consequences are not limited to the optical properties of systems. An electrical conductor for instance may be chiral because of several reasons. The material may crystallize in a chiral space group, like tellurium or /9-manganese [30], or be composed of chiral subunits like chiral conducting polymers [31] and Langmuir-Blodgett films [32] or vapors [33] of chiral molecules. Even if the material itself is nonchiral, it may still be formed into a chiral shape, like a helix. In all these cases, the conductor can exist in two enantiomeric forms. 

Chiral Charge Density Waves in Quasi One-Dimensional Organic Conductors 303... 

CHIRAL CHARGE DENSITY WAVES IN QUASI ONEDIMENSIONAL ORGANIC CONDUCTORS... 

Carbon nanotubes are one of the most important classes of new carbon materials. Distinctions are made between single- and multiwalled as well as between zig-zag, armchair, and chiral nanotubes. The structure is characterized by the descriptors n and m. These structural parameters allow for a prediction of the electric conductivity. Only armchair nano tubes n,n) and such species with m-n = iq are electric conductors. Any other nanotube is semiconducting. These statements have been established from symmetry considerations and from determining the band structure by way of the zone-folding method. There are different approaches to the production of single- and multiwalled nanotubes. Important methods of preparation are ... 

P20.36 Single-walled carbon nanolubes (SWNT) may be either conductors or semiconductors depending upon the tube diameter and the chiral angle of the fused benzene rings with respect to the lube axis. Van der Waals forces cause SWNT to slick together in clumps, which are normally mixtures of conductors and semiconductors. SWNT stick to many surfaces and they bend, or drape, around nano-sized features that are upon a surface. 

Cyclic sulfates also undergo double nucleophilic displacement by dianion 276 in methanol to give a 1 1 adduct, which cyclizes to 277 on heating. Compound 277 is used in chiral organic conductors and superconductors (86HCA69 93BCJ513 94T11205) [Eq. (47)]. 

There are two reasons for studying enantiomerically pure conductors. The first is connected with questions of structure. In effect, it is possible, starting from enantiopure bricks, to prepare crystal structures that are noncentrosymmetric, and which allow the disorder to be limited compared to the racemic derivatives. The second reason is linked to the fact that, for chiral conductors in an enantiopure form, theory predicts the existence of an effect called electrical magnetochiral anisotropy (EMCA) due to the simultaneous breaking of space and time symmetry in the presence of an external magnetic field. Thus, the resistivity of a chiral conductor depends on its absolute configuration according to the formula ... 

Rikken proposed that the EMCA effect could also result from the simultaneous application of a magnetic field and a current to a crystal with an enantiomorphous space group, and that it is a universal property. He showed the existence of this effect in the case of chiral single-walled carbon nanotubes.For most of the investigated tubes, a dependence of the resistance is observed that is odd in both the magnetic field and the current. These observations confirm the existence of EMCA not only for a macroscopic chiral conductor but also for a molecular conductor with chirality on the microscopic level. 

Coronado obtained an enantiopure molecular conductor by using Sb2((2P, 3P)-(+)-Tartrate)2 Sb2-(6.4)2 as the chiral inductor anion in the self-assembly. Electrocrystallization in the presence of (BEDT-TTF) yields a conductive compound with the formula [BEDT-TTF]3[Sb2((2P, 3P)-(+)-Tartrate)2]. CH3CN (6.18).CH3CN which crystallizes in the chiral space group P2i2i2i. It is composed of two subnetworks, one anionic and the other cationic, in alternate layers, with the BEDT-TTF perpendicular to the anionic layers and the cationic layers forming a helical structure (Figure 6.11). 

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