BEDT-TTF,

The structures of the black crystalline benzene solvate C6o-4C6H6, the black charge-transfer complex with bis(ethylenedithio)tetrathiafulvene, [C6o(BEDT-TTF)2], and the black ferrocene adduct [C6o Fe(Cp)2)2] (Fig. 8.7b) ) have also been solved and all feature the packing of Cso clusters. 

BEDT-TTF Bis(ethylenedithio)tetrathiafulvalene CCDC Cambridge Crystallographic Data Centre... 

IScm a large value when compared with other ( / structures such as (X-(BEDT-TTF)2(IC12). 

Following Dehnicke s report in 1996 on the co-crystallization of diiodoacety-lene (DIA) with various halide anions to form two-dimensional networks through C-I X interactions [93], Kato et al. investigated these supramo-lecular anions in the electrocrystallization of classical TTFs such as BEDT-TTF. 

Scheme 13 Polymeric anionic networks formed upon electrocrystallization of BEDT-TTF with X (Cl , Br ) in the presence of iodoalkynes or iodoperfluoroarenes...

Bi-5,6-dihydro-1,3-dithiolo[4,5-b][1,4]-dithiinylidene (BEDT-TTF). J. Larsen and C. Lenoir, Department of General and Organic Chemistry, H. C. Orsted Institute, University of Copenhagen,... 

We saw in Section 12.2.3.1 that the presence of additional chalcogen atoms in BEDT-TTF/TCNQ promotes interstack interactions, suppressing the Peierls distortion and imparting upon the salt increased dimensionality compared to TTF/TCNQ. The result of including a different chalcogen into the TTF/TCNQ structure is shown in Table 2. Despite losing donor efficiency compared to TTF (Table 1) the TCNQ complexes of m/trans-diselenadithiafulvalene (DSDTF, 55/56) and TSF show an improvement in conductivity when two or four selenium atoms are incorporated. The reduced metal-insulator transition suggests that this effect is also caused by a suppression of the Peierls distortion. Increased Se-Se interstack contacts add dimensionality to the structure and limit the co-facial dimerisation typical of Peierls distortion. Wider conduction bands are afforded from the improved overlap of diffuse orbitals. 

The electron-donor molecule most studied as a component of cation-radical salts is BEDT-TTF. Over 50 superconducting salts containing this molecule have been reported in the literature. Several distinct packing motifs [6-8] of the BEDT-TTF radical cations have yielded superconducting salts, but the most studied of these are... 

Scheme 2 Four common packing motifs of the BEDT-TTF molecule. The black bars represent and end-on view of the molecule, looking down the long molecular axis. The a-phase, which is quite similar to the 0-phase, is characterized as a herringbone structure, the P -phase contains stacks of slipped dimers, the K-phase contains orthogonally arranged dimers, and the P"-phase is characterized by canted stacks of donor molecules...

Fig. 1 Photograph illustrating the morphologies characteristic of the kl- and KH-phases of (BEDT-TTF)2M(CF3)4(solvent)...

Fig. 2 Packing diagram of the layered structure of kl-(BEDT-TTF)2Cu(CF3)4(TCE) (top). The packing motif of the BEDT-TTF electron donor molecules (lower left). The anion layer contains both disordered [Cu(CF3)4] anions and neutral TCE solvent molecules (lower right). In all cases, hydrogen atoms have been omitted for clarity...

An initial attempt was made to correlate the structural properties of the kl-(BEDT-TTF)2M(CF3)4(TCE) salts with their superconducting transition temperature [31]. The relationship between Tc and any single unit cell parameter failed to show any discemable trend. The best correlation was obtained by plotting Tc as a function of the b/c ratio, where b is the interlayer and c is an intralayer direction. A similar conclusion was reached through the determination of uniaxial pressure coefficients of p -(BEDT-TTF)2SF5CH2CF2S03 and k-(BEDT-TTF)2Cu(NCS)2 through the measurement of thermal expansion [32]. These results also indicated that expansion of the interlayer direction and compression of an intralayer direction... 

Fig. 3 Chart illustrating the superconducting transition temperatures as a function of solvent and anion in the KL-(BEDT-TTF)M(CF3)4(l,l,2-trihaloethane) (M = Cu, Ag and Au) series. 1120 is 1,1,2-trichoroethane, lBrl2Cl is l-bromo-l,2-dichloroethane, llC12Bris 1,1-dichloro-2-bromoethane, lC112Br is 1-chloro-1,2-dibromoethane and 112Bris 1,1,2-tribromoethane...

The effect of deuterium isotope substitution on Tc has been studied for three members of the KL-(BEDT-TTF)2Ag(CF3)4(l,l,2-trihaloethane) family [12, 34-36]. In all cases, the Tc increased upon deuteration with the effect ranging from 0.21 to 0.36 K. These results are similar to the deuterium isotope effect observed in the p"-(BEDT-TTF)2SF5CH2CF2S03 [34, 37] and k-(BEDT-TTF)2Cu(NCS)2 [38] superconductors. 

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