Crystal structures and electrical conducting/magnetic properties in 1 : 1 FeCl4 and FeBr4 salts of dimethylthio- and ethylenedithio-(1,3-dithiolylidene)thioxotetrathiafulvalene radical cations

The 1 : 1 radical cation salts of new donor molecules, dimethylthio- (1) an d ethylenedithio-(1,3-dithiolylidene)thioxotetrathiafulvalenes (2) with a m agnetic FeCl4 or FeBr4 counteranion (1.FeBr4, 2.FeCl4 and 2.FeBr4) were pre pared, and their electrical conducting and magnetic properties were investi gated. The room-temperature electrical conductivities of 1.FeBr4 (compresse d pellet), 2.FeCl4 (single crystal) and 2.FeBr4 (single crystal) were < 10( -5), 1.8 x 10(-4) and 7.0 x 10(-2) S cm(-1), respectively. The temperature dependence of paramagnetic susceptibility obeyed the Curie-Weiss law in all cases, and the Curie constant (C) and Weiss temperature (<theta>) were as follows: C=4.61 emu K mol(-1) and theta = -5.4 K for 1.FeBr4; C=4.53 emu K mol(-1) and theta = - 13.4 K for 2.FeCl4; C = 4.55 emu K mol(-1) and theta = -31.2 K for 2.FeBr4. The remarkably different theta values between the th ree salts, considered together with their crystal structures, suggest signi ficant interaction between Fe(III) spins by aid of pi spins on 1 or 2 molec ules.