Electronic Properties of a TMTTF-Family Salt, (TMTTF)2TaF6: New Member Located on the Modified Generalized Phase-Diagram

A new TMTTF (tetramethyl-tetrathia-fulvalene)-family salt, (TMTTF)(2)TaF6, which has the largest octahedral (O-h) symmetry counter anion among the various salts in the TMTTF family, was prepared. X-ray, static magnetic susceptibility, electron spin resonance (ESR) and nuclear magnetic resonance (NMR) measurements were carried out in order to investigate the electronic state of (TMTTF)(2)TaF6. The unit-cell volume of (TMTTF)(2)TaF6 is larger than that of (TMTTF)(2)MF6 (M = P, As, and Sb). (TMTTF)(2)TaF6 shows the highest charge-ordering phase transition temperature (7(CO) similar to 175 K) among TMTTF salts with the O-h-symmetry Counter anion. These facts indicate that (TMTTF)(2)TaF6 is located on the most negative side in the generalized phase-diagram for TMTCF family salts. (TMTTF)(2)TaF6 undergoes an anti ferromagnetic transition around 9 K. It turned out the phase diagram needs to be modified.