Interconvertible bistability in magnetic organic conductors based on bent donor molecules, EDO-EDSe-TTFVS(O)

Abstract

Electrochemical oxidation of a bent donor molecule ethylenedioxy-ethylenediseleno-tetrathiafulvaleno-thioquinone-1,3-dithiolemethide (EDO-EDSe-TTFVS, 1) and the corresponding quinone derivative EDO-EDSe-TTFVO (2) in the presence of (Bu₄N)MCl₄ (M = Ga, Fe) affords single crystals of three radical cation salts, 1₂FeCl₄, 1₂GaCl₄, and 2₂FeCl₄(DCE) (DCE = 1,2-dichloroethane). All of these salts exhibit semiconductor-to-semiconductor first-order phase transitions with a relatively large thermal hysteresis width (>15 K). The d-spins of FeCl₄⁻ ions in both 1₂FeCl₄ and 2₂FeCl₄(DCE) show relatively strong antiferromagnetic interactions with Weiss temperatures of −7.1 and −9.2 K, respectively. The antiferromagnetic interaction in both salts originates from the preferential d–π–π–d interaction. The crystal structures of both 1₂FeCl₄ and 1₂GaCl₄ are solved at 298 and 150 K, which correspond to the high- and low-temperature phases (H- and L-phases), respectively. In each phase, the crystal structures of 1₂FeCl₄ and 1₂GaCl₄ are isomorphous. The donor molecules in the H- and L-phases of 1₂FeCl₄ have similar packing patterns composed of one-dimensional columns with donor dimers. The phase transition of 1₂FeCl₄ is accompanied by a slight orientational change of donor molecules in a dimer, and the electron correlation is enhanced on cooling. On the basis of the “molecular coordinates”, the effect of the molecular rotation on the electronic phase transition is discussed. The results indicate that a slight molecular rotation can give rise to a significant change of electron correlation even in an electronic system with strong intermolecular interactions.