EDT-TTF-

EDT-TTF Ethylenedithio-tetrathiafulvalene SOMO Singly occupied molecular orbital... 

Scheme 4 Typical halogen bonded motifs involving a partially oxidized TTF molecule such as EDT-TTF-I with halide (top) or cyanometallate (bottom) counter ions...

The (EDT-TTF-I)2Br salt described above [36] and the 1 1 (TTFI4)I salt reported by Gompper [51] were the only structurally characterized salts with simple halide anions until Imakubo recently described an extensive series of Cl" and Br" salts from several ortho-diiodo tetrathiafulvalene, tetraselena-fulvalene and dithiadiselenafulvalene derivatives (Scheme 8) [62], The X-ray crystal structure analysis of the nine salts described there show a variety of halogen bonded motifs, demonstrating the adaptability of the supramolecu-lar interactions to other structural requirements imposed by the nature of the heteroatoms (O, S, Se) in the TTF frame. Indeed, in (EDT-TTF-l2)2X-(H20)2 (X = Cl, Br), a bimolecular motif (Fig. 6) associates two partially oxidized EDT-TTF-I2 molecules with one Br" anion and one water molecule. 

Moreover, it was shown that the presence of Hal Hal interactions between the partially oxidized molecules also contribute to the electronic delocalization. Indeed, the presence of non-zero atomic coefficients on the halogen atoms in the HOMO of EDT-TTF-Br2 or EDT-TTF-I2 [66], together with the short Hal Hal contacts, leads to a sizeable increase of the band dispersion and stabilizes a rare (V structure through the side-by-side arrangement of the inversion-centred dyads connected by Hal- Hal interactions. Both 13 salts are semiconductors with room temperature conductivities around... 

Only a few recent examples of halogen bonding of halogenated TTFs with halometallate anions have been described and this most probably represents a broad development field in this area. Indeed, these halometallate salts offer a wide variety of complexes and specifically here a large variation of the ratio of anion charge vs number of halide atoms, as already discussed above in the comparison between Br and 13 salts. This point is illustrated by the superb structures of two salts of EDT-TTF-I2 with the polymeric one-dimensional PbV (Fig. 9) and two-dimensional (Pbs/eDi/eh) anions where shorter C -1- -Ianion contacts are observed with the linear Pbl3 chains... 

Fig. 9 I-- I interactions in (EDT-TTF-l2)2(Pbl3) with the polymeric (Pbl3)co anionic chains... 

Fig. 11 The trimeric motif formed upon halogen bonding interaction between the partially oxidized EDT-TTF-I2 and the dithiolene complex [NilmnthF...

Scheme 10 Inverting the polarity of halogen bonding with EDT-TTF-CN...

Since then seven further superconducting (at low temperatures and/or under high pressures) dmit-based complexes with Ni or Pd as metal, synthesized via electrocrystallization, have become known. The donor-acceptor complex a-(EDT-TTF)[Ni(dmit)2]2 is the first ambient pressure superconductor with Tc = 1.3 K.257 ... 

Fig. 3 Ambient-pressure superconductivity in a-(EDT-TTF) [Ni(dmit)2]. The inset shows the superconductive transition at 1.3 K. Redrawn after [42]...

Among the M(dmit)2-based superconductors, a-(EDT-TTF)[Ni(dmit)2] is also of donor-acceptor type and has two outstanding features it is the only one to contain a 1 1 molar ratio of donor and acceptor units and to exhibit superconductivity at ambient pressure [32]. It was found to be superconductive below 1.3 K under ambient pressure (Fig. 3). 

Figure 2.5. Scheme of the preparation of EDT-TTF by different synthetic routes (strategies S2, S3, S4 and S5). Increasing arrow width indicates higher selectivity (S4 is completely selective). 

---