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-

Salts of the donor molecule, bis(ethylenedithio)tetrathiafulvalene (BEDT-TT F or ET), with pentafluorothiomethylsulfonate (SF5CX2SO3-, X = H or F) anio ns have been prepared. Three phases, beta"-(ET)(2)SF5CH2SO3, beta'-(ET)(2)S F5CF2SO3, and beta"-(ET)(2)SF5CHFSO3 were obtained by electrocrystallizatio n with the corresponding LiSF5CX2SO3 electrolytes. The structures of these salts were determined by sing;le-crystal X-ray diffraction, and their physi cal properties were examined by electrical resistivity measurements as well as by ESR and Raman spectroscopy. The beta"-(ET)(2)SF5CH2SO3, beta-(ET)(2) SF5CHFSO3 and beta-(ET)(2)SF5CF2SO3 salts are considerably different in the ir crystal structures, physical properties, and electronic structures despi te the similarity in the structures of the SF5CX2SO3- (X = H, F) anions. Th e beta"-(ET)(2)SF5-CH2SO3 salt has two kinds of ET donor molecules with con siderably different charge densities. The electronic structure of beta"-(ET )(2)SF5CHFSO3 has both one-dimensional (1D) and two-dimensional (2D) Fermi surfaces which are similar to those found in the organic superconductor bet a"-(ET)(2)SF5CH2CF2SO3. The ESR data for the beta'-(ET)(2)SF5CF2SO3 salt in dicate 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 i nteraction energies between nearest-neighbor ET molecules in their donor mo lecule layers.