A -TTF Pd

S---S interactions. It should be noted that a- and a -[TTF][Pd(dmit)2]2 phases are isostructural with [TTF] [Ni(dmit)2]2 and exhibit the same network of S---S interactions. In [Me4N]o.5[Ni(dmit)2], sheets containing... 

Some needle-shaped crystals of a -TTF[Pd(dmit)2]2 [lc,ld,27] are also isostructural with TTF[Ni(dmit)2]2-This phase also undergoes a metal-to-insulator transition at around 220 K. However, this transition is completely reversible and shows no hysteresis [27]. The effect of high pressure is the suppression of this metal-to-insulator transition. The superconducting transition is observed at 5.93 K and 24 kbar [Id]. A gradual localization of the carriers is observed at low pressure, which can be related to a charge density wave condensation evidenced by X-ray diffuse scattering experiments [23]. a -TTF[Pd(dmit)2]2 is the first example in which competition between CDW and superconductivity is observed. 

With the aim of increasing the dimensionality through I S interaction, Imakubo et al. (99) used the IEDT-TTF donor molecule (IEDT-TTF = CxH5S6l, iodoethylenedithiotetrathiafulvalene) (see Scheme 11) derived from EDT-TTF by substituting an iodine for one hydrogen atom on the TTF moiety. Indeed, the crystal structure of (IEDT-TTF)[Pd(dmit)2] reveals T S distances of 3.308(4) A, shorter than the sum of the van der Waals radii (4.0 A), indicating strong I S interactions. Due to these I - S interactions, the donor and the Pd(dmit)2 units are almost parallel, which is not the case in the parent (EDT-TTF)2[Pd(dmit)2]2 compound (97, 98). The complex (IEDT-TTF)[Pd(dmit)2] behaves like a metal down to 4.2 K, whereas (EDT-TTF)2[Pd(dmit)2]2 remains metallic at lower temperatures (500 mK) (97). 

Figure 5. The complex a -(EDT-TTF)[Pd(dmit)2]. Pressure-dependence of the resistivity a, ambient pressure b, 2 c, 5 d, 10 kbar) and (insert) non-ohmic behavior at ambient pressure for an injected current of 150 pA ( ) and 1.5 mA (—). [Adapted From (97).]...

Interdiffusion of saturated solutions (as opposed to electrocrystallization) is another method for obtaining crystals of the potentially conducting salts. In most of the preparations of TTF[Pd(dmit)2]2 (dmit 3-Xn, X, Y, Z = S) by diffusion of (TTF)3(BF4)2 and (n-Bu2N)[Pd(dmit)2] mainly black shiny needles of the a phase were obtained. However, some experiments yielded, in addition, the so-called a phase (due to its structural similarity to the a phase, but different electrical behaviour), and occasionally a third 5 phase of plate-shaped crystals could also be physically separated from the batch (Legros and Valade 1988 Cassoux et al. 1991). ... 

A TTF aspartic acid derivative and its corresponding di-, tri-, and tetrapeptides have been recently synthesized [185]. The voltammetry of the TTF amino acid showed similar behavior to that found for unsubstituted TTF, except that the redox potentials (E pd) and p(2)) re shifted toward the anodic by 153 and 47 mV, respectively. In contrast, the voltammetry of the peptides showed broadening of the first redox wave but not of the second wave. Further experiments indicated that there are intramolecular, but no inter-molecular, interactions between the TTF groups. 

A mixed-valence complex of metal(dmit)2 (H2dmit = 4,5-dimercapto-l,3-dithiolo-2-thione) system is one of the promising candidates for the preparation of conductive LB films with higher dimensionality [27]. This sulfur-rich 1,2-dithiolene complex has provided three molecular superconductors, TTF[Ni(dmit)2]2 [28], TTF[Pd(dmit)2l2 [29], and Me4N[Ni(dmit)2]2 [30]. By the introduction of the alkylammonium group as a counter cation, the complexes become amphiphilic, and suitable for the construction of LB films. 

Figure 5.34. Segregated stacks of EDT-TTF piling up along [100] and [Pd(dmit)2] stacked along [101] in a -(EDT-TTF)[Pd(dmit)2]. (Reprinted with permission from ref. 31)...

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