Magnetoresistance Effects Evidencing the π−d Interaction in Metallic Organic Conductors, (EDT-DSDTFVO)<sub>2</sub>•MX<sub>4</sub> (M = Fe, Ga; X = Cl, Br)

The 2:1 salts of a new donor molecule, EDT-DSDTFVO with MX<sub>4</sub><sup>-</sup> (M = Fe, Ga; X = Cl, Br) ions, were prepared. The crystal structures of the donor molecules had a β-type packing motif. All the salts essentially exhibited metallic behaviors despite the small upturns in the resistances below 30−70 K. A large negative magnetoresistance (MR) effect [−14.7% (ρ<sub>⊥</sub>) at 4.0 K and 5 T] was observed in the FeCl<sub>4</sub><sup>-</sup> salt, while a positive MR effect [+4.0% (ρ<sub>⊥</sub>) at 4.0 K and 5 T] was observed in the GaCl<sub>4</sub><sup>-</sup> salt, suggesting that there is a π−d interaction in the FeCl<sub>4</sub><sup>-</sup> salt. The pressure application suppressed the resistivity upturns, increased the negative MR effect (−17.7% at 9.5 kbar) in the FeCl<sub>4</sub><sup>-</sup> salt, and decreased the positive MR effect (+3.3% at 15 kbar) in the GaCl<sub>4</sub><sup>-</sup> salt.