Electrical conductivities and crystal and band-electronic structures of a new phase of BEDT—TTF—bromide salt, (BEDT—TTF)2Br(H2O)3

A new bromide salt of BEDT-TTF, (BEDT-TTF)2Br(H2O)3, was obtained by an electrochemical crystallization of the tetrahydrofuran (THF) solution containing BEDT-TTF, malonic acid, and aqueous tetrabutylammonium hydroxide. Commercially available aqueous Bu4NOH contaminates Br−, which is the anion source of this salt. The temperature dependence of the electrical resistance showed a complex behavior, but the resistance decrease in the low temperature range suggests a metallic ground state down to 4.2 K. Its crystal structure belongs to the δ-type, the example of which was found for δ-(BEDT-TTF)2AuBr2. A tight-binding band structure calculation revealed a closed Fermi surface, characteristic of a two-dimensional band structure.