Abstract

The 1 ∶ 1 radical cation salts of new donor molecules, dimethylthio- (1) and ethylenedithio-(1,3-dithiolylidene)thioxotetrathiafulvalenes (2) with a magnetic FeCl₄ or FeBr₄ counteranion (1·FeBr₄, 2·FeCl₄ and 2·FeBr₄) were prepared, and their electrical conducting and magnetic properties were investigated. The room-temperature electrical conductivities of 1·FeBr₄ (compressed pellet), 2·FeCl₄ (single crystal) and 2·FeBr₄ (single crystal) were <10⁻⁵, 1.8 × 10⁻⁴ and 7.0 × 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 (θ) were as follows: C = 4.61 emu K mol⁻¹ and θ = −5.4 K for 1·FeBr₄; C = 4.53 emu K mol⁻¹ and θ = −13.4 K for 2·FeCl₄; C = 4.55 emu K mol⁻¹ and θ = −31.2 K for 2·FeBr₄. The remarkably different θ values between the three salts, considered together with their crystal structures, suggest significant interaction between Fe(III) spins by aid of π spins on 1 or 2 molecules.