Crystal structure and physical properties of (EDO-TTFBr2)2FeX4(X = CI, Br)

Abstract

The crystal structure and physical properties of radical ion salts (EDO-TTFBr 2 ) 2 FeX 4 (X = Cl, Br) composed of halogen-substituted organic donor and magnetic halide anions are investigated. The salts consist of uniformly stacked donor molecules, whose Br substituents are connected to halide ligands of anions with remarkably short intermolecular contacts. Both salts show metallic behavior above ca. 30K. The FeCl 4 salt shows an antiferromagnetic (AF) transition at T N = 4.2K despite the absence of anion...anion contacts, thus the magnetic interaction between the localized spins on the anions is mediated by the π-d interaction through the Br...Cl contacts. For the FeBr 4 salt the AF transition temperature is elevated to T N = 13.5K, accompanied with another anomaly at T C2 = 8.5K. This behavior can be qualitatively explained by a magnetic structure model where the π-d interaction between donor and anion is taken into account.