Comparison of the Crystal and Electronic Structures of Three 2:1 Salts of the Organic Donor Molecule BEDT-TTF with Pentafluorothiomethylsulfonate Anions SF₅CH₂SO₃^-, SF₅CHFSO₃^-, and SF₅CF₂SO₃^-

Abstract

Salts of the donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), with pentafluorothiomethylsulfonate (SF5CX2SO3-, X = H or F) anions have been prepared. Three phases, β‘ ‘-(ET)2SF5CH2SO3, β‘-(ET)2SF5CF2SO3, and β‘ ‘-(ET)2SF5CHFSO3 were obtained by electrocrystallization with the corresponding LiSF5CX2SO3 electrolytes. The structures of these salts were determined by single-crystal X-ray diffraction, and their physical properties were examined by electrical resistivity measurements as well as by ESR and Raman spectroscopy. The β‘ ‘-(ET)2SF5CH2SO3, β‘ ‘-(ET)2SF5CHFSO3 and β‘-(ET)2SF5CF2SO3 salts are considerably different in their crystal structures, physical properties, and electronic structures despite the similarity in the structures of the SF5CX2SO3- (X = H, F) anions. The β‘ ‘-(ET)2SF5CH2SO3 salt has two kinds of ET donor molecules with considerably different charge densities. The electronic structure of β‘ ‘-(ET)2SF5CHFSO3 has both one-dimensional (1D) and two-dimensional (2D) Fermi surfaces which are similar to those found in the organic superconductor β‘ ‘-(ET)2SF5CH2CF2SO3. The ESR data for the β‘-(ET)2SF5CF2SO3 salt indicate that it opens a spin gap below 45 K. The differences in the physical properties of the three salts were analyzed by calculating the HOMO−HOMO interaction energies between nearest-neighbor ET molecules in their donor molecule layers.