Chiral TTFs

A chiral TTF-substituted poly(isocyanide) 11 was prepared by Amabilino et al. 

A great number of chiral TTFs have been prepared [31,32], and some of their charge transfer salts have been crystallised. The 7r-donor 1 can be elec-trocrystallised to give a salt 12 PF6, which has a conductivity of 5 2 1 cm 1 at room temperature and metallic behaviour when cooled down [33]. While the structure of the crystals is chiral, the structure of this salt and other related ones [34] has an essentially achiral stack of donor molecules, which are pseudo-centrosymmetric [35]. The methyl groups at the periphery of the molecule are apparently not sufficient to cause a truly chiral stack of donors, which prefer to stack in parallel arrangements with partial overlap of the tr-systems in the solid state, a situation which is true for the majority of the efforts to prepare salts of this type (even if the salts are metallic). 

This requirement to planarity is important but not very strict. The salt [(TTF)+ (TCNQ) ] is an example. It possesses metallic conductivity. However, its fulvalene rings are not strictly coplanar and the cyano groups are, to a certain degree, bent in respect of the quinone ring. Moreover, one organic metal has been prepared on the basis of the principally nonplanar chiral ion-radical (TMET)2 PFg . Its conductivity is equal to 5 cm at ambient conditions (Wallis et al. 1986). 

Oxidation of TTF and its derivatives induces the transformation from neutral species into cationic ones, namely, cation radicals (TTF +) and dications (TTF2+). Moreover, TTF, TTF +, and TTF2+ exhibit different absorption spectra. Taking these advantages of TTF new TTF-based redox fluorescence switches and chiral switches have been recently reported. 

Chiral binaphthalene (/f)-10 with two substituted TTF and trichloroquinone units was synthesized.21 It is expected from such system, that the variation of the D-A interaction in the presence of metal ions may induce a change of the dihedral angle between the two naphthalene rings. Both absorption and ESR spectral studies show that electron transfer occurs between TTF and trichloroquinone units in the presence of metal ions. Nevertheless, in contrast to expectation, the CD spectral change of (7 )-10 is rather small after addition of metal ions. 

Fig-1 TTF and some of the chiral donor molecules derived from it... 

We discuss the interaction of a partially filled electronic conduction band in a segregated donor-acceptor stack system with libra-tional modes of the solid. The orientational Peierls instability predicted by us earlier leads to the formation of chiral charge density waves, which interact and phase-lock below the metal-insulator transition via the Coulomb interaction. The effect of the resulting order on the physical properties of the system and the implications for the understanding of the recent neutron scattering data for the occurrence of several transitions in TTF-TCNQ will be discussed. 

We propose in this paper that the observed Peierls instability in TTF-TCNQ and the richness of structural transitions arises from the interaction of the tt electron and hole system on separate TCNQ and TTF chains, respectively, with orientational modes (librons) of the solid. We suggest, that the chiral charge density waves (CCDW), which result from the orientational distortion of the TCNQ and TTF stacks account for the observed continuous increase in the unit cell dimension from a = 2a at 54° to a = 4a at 38°K. 

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). 

Sb2((25, 35)-(+)-Tartrate)2].CH3CN IS, 35)-(6.18).CH3CN has a CD spectrum that is symmetrical with the first. The observed Cotton effects are not related to those of the antimonyl tartrate, which is found below 240 nm, but to the BEDT-TTF cationic network, confirming that the whole structure is chiral. Physical measurements show that the material is an enantiopure semiconductor although, except for the CD, it is not possible to attach any particular property to the material s enantiopure chiral character. Following the same synthetic strategy, a salt of BEDT-TTF with the polyoxometalate... 

ORGANIC METALS FROM CHIRAL BEDT-TTF DONORS... 

The versatility of this organic counterpart of the well-known inorganic layered solids opens the possibility for systematic "chemical variation of band fillings and electronic interactions. The redox properties of the different lattice elements can be varied systematically by chemical methods, since the BEDT-TTF salts are open to synthetic variations in both types of layers very similar to the famous inorganic ternary oxides. So far, most of the recent work to vary the physical properties by chemical action concentrated on the preparation of BEDT-TTF salts with a wide variety of anions. Fewer efforts were concerned with a systematic variation of the BEDT-TTF moieties [6]. One major problem arises in the pursuit of the latter goal the substitution of the periphery hydrogen atoms could lead to a manifold of chiral molecules. 

We have shown that is is possible to obtain organic metals from chiral molecules. The X-ray results prove an oxidation number of +1.5 for the radic cations in at least two cases. To our best knowledge, these are the first examples of BEDT-TTF-related radical cation salts... 

TTF Radical Cations Salts Toward Chiral Conductors. 94... 

The structure of this phase (Figure 3.10 and 3.11), where EDO-5,5 -DMEDT-TTF is the unsymmetrical donor molecule (12c-5,5-7f), with a chiral structure. 

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