Charge-Transfer Salts Derived from the New Electron-Donor Molecule BEDO-TTF: ESR, Superconductivity and Electrical Properties, and Crystal and Band Electronic Structure

Abstract

Charge transfer salts of bis(ethylenedioxy)tetrathiafulvalene, BEDO-TTF, namely (BEDO-TTF)₂AuBr₂, and charge transfer salts (BEDO-TTF)_mX_n where X⁻ is I₃, AuI₂ ⁻, Au(CN)2⁻, ClO₄ ⁻, BrO₄ ⁻, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, NO₃ ⁻, C(CN)₃ ⁻, and HgBr₃− have been synthesized. The AuBr₂− salt is the first BEDO-TTF salt to be structurally characterized. Crystallographic investigations of several of the other (BEDO-TTF)_mX_n salts have shown that (with the exception of the I₃− salt) these new synmetals are structurally very similar to (BEDO- TTF)₂AuBr₂. Therefore, a 2:1 stoichometry is expected for BEDO-TTF salts. The observation of similar ESR linewidths for all the BEDO-TTF salts reinforces this conclusion. While (BEDO-TTF)₂PF₆ is semiconducting and the AuBr₂−, Au(CN)₂−, and ClO₄− salts are metallic only near room temperature and semiconducting at low temperatures, (BEDO-TTF)₂AuI₂ shows metallic conductivity to low temperatures. RF penetration depth measurements on crystals derived from BEDO-TTF/KSCN/CuSCN show the occurence of superconductivity near 1 K. Band electronic structure calculations on (BEDO-TTF)₂AuBr₂ and (BEDO-TTF)₂ClO₄ indicate that they are one-dimensional metals.