ET based conductors with different behavior of resistivity along and across conducting layers

Abstract

A series of novel bis(ethylenedithio)tetrathiafulvalene (ET) based radical cation salts with tetrahedral [HgBr 4] 2− and [CdBr 4] 2− dianions of (ET) 4MBr 4(solvent) stoichiometry (M = Hg, Cd; solvent = C 6H 5X or 1,2-C 6H 4X 2, X = Cl, Br) has been prepared. Crystal structures of θ-(ET) 4HgBr 4(1,2-C 6H 4X 2) (X = Cl, Br) were found to involve conducting ET radical cation layers of the θ-type packing and insulating layers consisting of [HgBr 4] 2− anions and solvent molecules. The donor stacking directions of the neighboring conducting layers are perpendicular to each other. Depending on salt composition, intralayer electrical resistivity of θ-(ET) 4MBr 4(solvent) showed metal-like behavior down to temperatures varying within 4.3–100 K range. Electrical resistivity perpendicular to the layers revealed nonmetallic behavior. The study of magnetoresistance of θ-(ET) 4HgBr 4(1,2-C 6H 4Cl 2) revealed Shubnikov-de Haas oscillations in fields up to 15 T with the only frequency F = 900 T. The θ-(ET) 4MBr 4(C 6H 4Cl 2) M = Hg, Cd compounds are the first ET-based conductors which show metallic behavior of conductivity in layers and semiconducting behavior across layers down to 4.3 K.