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 (SF 5 CX 2 SO 3 -, X ) H or F) anions have been prepared. Three phases, β′′-(ET) 2 SF 5 CH 2 SO 3 , β′-(ET) 2 SF 5 CF 2 SO 3 , and β′′-(ET) 2 SF 5 CHFSO 3 were obtained by electrocrystallization with the corresponding LiSF 5 CX 2 SO 3 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) 2 SF 5 CH 2 SO 3 , β′′-(ET) 2 SF 5 CHFSO 3 and β′-(ET) 2 SF 5 CF 2 SO 3 salts are considerably different in their crystal structures, physical properties, and electronic structures despite the similarity in the structures of the SF 5 CX 2 SO 3 -(X ) H, F) anions. The β′′-(ET) 2 SF 5 -CH 2 SO 3 salt has two kinds of ET donor molecules with considerably different charge densities. The electronic structure of β′′-(ET) 2 SF 5 CHFSO 3 has both one-dimensional (1D) and twodimensional (2D) Fermi surfaces which are similar to those found in the organic superconductor β′′-(ET) 2 SF 5 CH 2 CF 2 SO 3 . The ESR data for the β′-(ET) 2 SF 5 CF 2 SO 3 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 nearestneighbor ET molecules in their donor molecule layers.

Charge ordering and antiferromagnetic exchange in layered molecular crystals of theθtype

“…There is controversy about whether nuclear magnetic resonance measurements can distinguish these two charge orderings. 64 The charge distribution observed 14 for ␤Љ-(BEDT-TTF) 2 SF 5 CH 2 SO 3 is consistent with charge ordering considered here.…”

“…Band structure calculations 14,17,27,30,31 predict that all these materials are metallic. Hence, the different phases must be due to electronic interactions.…”

“…The family ␤Љ-(BEDT-TTF) 2 SF 5 Y SO 3 has been studied 14 with Y ϭCH 2 CF 2 , CH 2 , CHF. The first material is superconducting with a transition temperature of 5.2 K. Y ϭCH 2 is insulating with a charge gap of 56 meV and evidence for charge ordering is found in the fact that alternate molecules have the bond length and phonon frequency associated with the central carbon double bond different.…”

“…13 Insulating, charge-ordered, and spin-gapped phases are observed for different anions. 14 Given the complexity of the details of the chemistry, crystal structure, and band structures of these materials it is important to define the simplest possible many-body Hamiltonian that can capture the essential physics. This is similar in spirit to the way one studies the Hubbard and t-J models on a square lattice in order to understand the cuprate superconductors.…”

Cu(I) coordination complex with TTF-based radical cation ligand

“…The most significant feature in this X-ray crystal data is that the distance of the central C5@C6 bond (1.388 (16) Previous theoretical studies have suggested that the HOMO of BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) includes the central C@C bonding and immediate four C-S anti-bonding orbitals of BEDT-TTF. Both the lengthening of the central C@C bond distance and the lessening of the immediate C-S bond distances have previously been predicted, based on the removal of one electron from the HOMO, leading to the generation of the TTF cation radical [10,11]. The change in the bond distances of CET-EDTTTF upon the formation of the complex analogously indicates that the oxidation of the CET-EDTTTF unit takes place, resulting in the formation of the radical species with the spin density mostly residing on the central S 2 C@CS 2 p-system.…”