New Cation-Anion Interaction Motifs, Electronic Band Structure, and Electrical Behavior in β-(ET)2X Salts (X = ICl2- and BrICl-)

Article abstract of DOI:10.1021/ja00264a020

Two new organic metals, β-(ET)2ICl2 and β(ET)2BrICl, were synthesized, and their structures and electronic properties were characterized via X-ray diffraction, ESR studies, and band electronic stucture calculations.BEDT-TTF, abbreviated "ET", is bis(ethylenedithio)tetrathiafulvalene, C10S8H8.The packing of the ET molecules within the sheetlike network of these two isostructural salts is significantly different from that of the two-dimensional metals β-(ET)2X with the larger anions X^- = I3^-, I2Br^-, IBr2^-, and AuI2^-, where all but X^- = I2Br^- are ambient-pressure superconductors.The ESR studies for the β-(ET)2ICl2 salt show that it is metallic down to ca. 22 K, at which temperature a metal-insulator transition is observed.The band electronic structures calculated for β-(ET)2ICl2 and β-(ET)2BrICl reveal that these salts are one-dimensional metals.Comparison of the stuctures and electronic properties of the β-(ET)2X salts with large linear anions (e.g., X^- = I3^-, I2Br^-, IBr2^-, and AuI2^-) vs. those with the small symmetric (Cl-I-Cl)^- and asymmetric (Br-I-Cl)^- anions leads us to conclude that the nature of the interactions between ET molecules within a given sheetlike network, and hence the dimensionality of electrical properties, is strongly governed by the packing motif of ET molecules around a particular X^- anion.