Synthesis of a new donor, BEDT-HBDST and crystal structures, electrical and magnetic properties of (BEDT-HBDST)2MX4 (M=Fe, Ga, X=Cl, Br), where BEDT-HBDST=2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5- tetrahydrothiophene

A novel conjugation-elongated bis(ethylenedithio)tetraselenafulvalene (BETS) type donor, 2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5- tetrahydrothiophene (BEDT-HBDST) and its magnetic and non-magnetic anion salts, (BEDT-HBDST)2MX4 (MX4-=FeCl4-, GaCl4-, FeBr4- and GaBr4-), were prepared. These four salts are isostructural and belong to the space group of P2/c. They showed semiconducting behavior with small activation energies (59-64 meV). The band structures of these salts are quasi one-dimensional and there is a midgap between the upper band and the lower band, since the degree of dimerization is significant in the stacking direction. The MX4- ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl4- and FeBr4- salts follow the Curie-Weiss law with Curie constants of 4.6 and 4.8 emu K mol-1 (sum of the spins of S=5/2 and S=1/2) and negative Weiss temperatures of θ=-1.2 and -4.9 K, respectively, revealing a weak antiferromagnetic interaction of 3d spins of the FeCl4- and FeBr4- anions. The Fe···Fe (6.66-7.60 A), Cl···Cl (4.81-4.82 A) and Br···Br (4.74-4.77 A) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe3+ ions appears to be not readily accessible