Two-dimensional organic metals θ-(BETS)4MBr4(PhBr), M = Cd, Hg with differently oriented conducting layers

New bis(ethylenedithio)tetraselenafulvalene (BETS) based radical cation salts with tetrahedral dianions [CdBr4]2− and [HgBr4]2− of the (BETS)4MBr4(PhBr) composition were prepared by electrochemical crystallization. Room-temperature crystal structure of (BETS)4CdBr4(PhBr) determined by single crystal X-ray diffraction involves BETS radical cation layers of the θ-type packing and insulating layers consisting of [CdBr4]2− anions and PhBr molecules. In the neighboring conducting layers, the stacks are arranged perpendicular to each other. A metal-to-metal transition within 225–230 K range was found in both (BETS)4CdBr4(PhBr) and (BETS)4HgBr4(PhBr). The behavior of electrical resistivity of these salts differs substantially along and across conducting layers. The study of magnetoresistance of (BETS)4HgBr4(PhBr) revealed weak Shubnikov-de Haas oscillations in fields higher than 6 T.