TMTSF

Figure 2 Side view of the stacks in (TMTSF)C104...

Exactly this approach led to the discovery of the first organic superconductors, the Bechgaard CT salts of tetramethyltetraselenafulvalene (TMTSF, 3) with various counteranions (TMTSF)2PF6 (under pressure) in 1980120 and... 

Saito et at.130 studied the salts of TMTSF and the sulfur analogue tetra-methyltetrathiafulvalene, TMTTF, with a polycyano dianion. Although the conductivity of both compounds was low (crrt = 10-5 Scm-1 for TMTSF vs. 10-7 Scm-1 for TMTTF) the conductivity of the Se-donor salt was improved by two orders of magnitude. Optical absorption spectroscopy was also used to assess the materials. The electronic transition between radical cations within the segregated donor columns occurred at considerably lower energy (8800 cm-1) in the TMTSF salt than in the TMTTF (11500 cm-1). A concurrent improvement... 

The synthesis of the bis-l,3-dithiolium radical cation (TTF+) in 1970 [1] enabled dramatic growth in the field of molecular conductors in the decades thereafter. TTF and several of its homologues are depicted in Scheme 1. The field of low dimensional molecular metals was further motivated by the discovery of the TTF-TCNQ charge-transfer complex in 1973 [2, 3]. Seven years later, superconductivity was induced in the cation-radical salt, (TMTSF)2PF6, upon application of 12 kbar pressure [4]. Shortly thereafter, superconductivity below 1.4 K was observed at ambient pressure in the perchlorate analog [5]. 

Jerome D, Mazaud A, Ribault M, Bechgaard K (1980) Superconductivity in a synthetic organic conductor, (TMTSF)2PF6. J Phys Lett 41 L95-L97... 

As will be discussed later (Section 1.5), molecules containing no metallic elements are able to combine and form materials exhibiting metallic character, e.g., HMTSF-TCNQ, TTF-TCNQ, etc., or even lose any electrical resistance below a given temperature and thus become superconductors, e.g., (TMTSF)2C104. Metal-free molecules can also, in the solid state, show magnetic order, such as / -NPNN and /7-NC-C6F4-CNSSN, where in the absence of -electrons the magnetic properties are related to unpaired -electrons. 

Dlh TTF, TCNQ, TMTTF, TMTSF, BEDT-TTF, PTCDA, Ni(dmit)2, BEDT-TSF, BDA-TTP, pentacene... 

TMTSF)2C104 exhibits Tc - 1 -4 K at P = 0 GPa, hence becoming the hrst organic superconductor at ambient pressure (Bechgaard etal, 1981). The tetrahedral... 

CIO4 ion being smaller than the octahedral PFg ion, the TMTSF sheets become closer to each other, chemically inducing the same effect as the physical hydrostatic pressure. When replacing TMTSF by TMTTF one obtains the isostructural Fabre salts. 

We saw in Section 1.1 for N2 that electron localization implies insulating ground states and that localization can be reduced by applying external pressure. When reducing temperature from RT down to about 20 K, (TMTTF)2X and (TMTSF)2X... 

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