Characterization of quasi-1D conductors, (BDTFP)2X(PhCl)0.5 (X=PF6, AsF6)

We present the low-temperature crystal structures of (BDTFP)2PF6 and (BDTFP)2AsF6 below the phase transition temperatures (Tp). In the former compound, the c-axis is doubled and thus the dimerized structure changed into a tetramerized structure. At the same time, a new charge-transfer (CT) transition appears at 7000–8000 cm−1. These two findings are consistent with the non-magnetic state below Tp. In the latter, on the other hand, the dimerized structure is maintained below Tp, and instead AsF6 ion rotates along with the ca. 10° rotation of BDTFP. This structural change is the origin of the first-order phase transition to a paramagnetic state.