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

Abstract

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) 2 MX 4 ( MX 4 −=FeCl 4 −, GaCl 4 −, FeBr 4 − and GaBr 4 −), 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 MX 4 − ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl 4 − and FeBr 4 − 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 FeCl 4 − and FeBr 4 − anions. The Fe⋯Fe (6.66–7.60 Å), Cl⋯Cl (4.81–4.82 Å) and Br⋯Br (4.74–4.77 Å) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe 3+ ions appears to be not readily accessible.