Crystals of the 2: 1 salts of a new donor molecule, benzotetrathiafulvalenoquinone-1,3-dithiolemethide (4, Benzo-TTFVO) with magnetic FeX4- and non-magnetic GaX4 - (X = Cl, Br) ions, 42·FeX4 and 4 2·GaX4, are isostructural to each other and showed a β-type packing of the donor molecules where they form a uniform-stacked structure with an interplanar distance of 3.50 Å. These salts exhibited metallic behavior down to 140-170 K, but at these temperatures (∼T M-I) an abrupt increase in the resistivities (ρ) occurred and thereafter semiconducting behavior with an activation energy of 40-100 meV was observed. A structural change in the donor column from uniform to tetramer-unit stacks was observed in the 42·FeBr4 crystal before and after TM-I. By application of pressures up to 1.0 GPa, the metallic behavior in the higher temperature region was gradually strengthened and TM-I gradually became lower with increasing pressure, but the transitions could not be suppressed at all. In response to the metal-semiconductor transition at TM-I, there was a sharp decrease in the paramagnetic susceptibility of the π electron system, where the transition from Pauli paramagnetism due to the metal-conducting behavior to the spin singlet state caused by tetramer formation of the donor molecules was observed. In addition, the FeX4- (X = Cl, Br) salts showed comparatively strong antiferromagnetic interactions between the Fe(iii) d spins of the FeCl4- and FeBr4- ions (Weiss temperature: -11 K for 42·FeCl4 and -37 K for 42·FeBr4), giving rise to antiferromagnetic orderings at 1.6 K for 42·FeCl4 and 9.3 K for 42·FeBr4. The magnitudes of the d-d and π-d interactions in 42·FeBr4 are calculated to be Jdd = 2.06 K and Jπd = 2.32 K, respectively. The comparison of these J values with the other magnetic conductors based on our system suggests that the d-d interaction of 42·FeBr 4 is stronger than the π-d interaction. Since the three-dimensional antiferromagnetic ordering appears at the comparatively high temperature of 9.3 K, there is an important contribution of the π electrons to the antiferromagnetic ordering of the Fe(iii) d spins in order to mediate the magnetic interaction between two-dimensional magnetic anion layers.
ASJC Scopus subject areas
- Materials Chemistry