TMTSF triclinic

We saw previously the example of TMTSF thin films where the lattice parameters could be obtained, and proof that the triclinic phase coincides with that found for... 

It is worth noting that when trying to obtain other polymorphs of Bechgaard salts incorporating octahedral, fluorine-containing anions as in (TMTSF)2PF6 or (TMTSF)2ShF6 only the triclinic phase is obtained. 

As mentioned above, all members of the TM2X series are isostructural compounds and no major difference could be expected at first glance between the four sulfur (TMTTF)2PF6 and the four selenium (TMTSF)2C104 compounds. They both exhibit the typical zigzag molecular packing (triclinic symetry) with two molecular units per unit cell (i.e., a formally half-filled band). 

The crystal structures of the two systems are also very alike. Both are triclinic with comparable unit-cell parameters and with the "herring-bone" structure known from TTF-TCNQ /8/. The most pronounced crystallographic difference between the two systems is a rather elongated /6.1 %/ b-axis in TMTSF-DMTCNQ. This is to be expected because the b-direc-tion is across the width of the molecules where the additional methyl-groups tend to push the chains apart thereb. y probably reducing the interchain coupling. 

The unusual electrical properties of the 2 1 TMTSF salts are summarized and discussed elsewhere. For additional characterization purposes beyond chemical analyses, the crystallographic lattice constants for the isostructural (triclinic, space group PT) TMTSF derivatives discussed here are given in Table I. 

Fig. 10.5 (TMTSF)2PF6 a phase diagram for the transition temperature as a function of the applied pressure. The data points are due to different authors. At low temperatures and low applied pressures, one observes the behaviour of an insulator with spin-density waves. At low temperature and high pressure, the substance is superconducting at higher temperature it is metallic. Crystallographic data triclinic, a = 7.29 A, b = 7J A,c= 13.52 A, = 83.39°, = 86.27°,... 

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