The 1:1 salt of a new donor molecule, ethylenedithiotetrathiaful-valenothioquinone-ethylenedithio-1,3-dithiole methide (1), with FeBr4- ion, 1.FeBr4, was prepared and found to exhibit a room-temperature electrical conductivity of 4 x 10(-2) S cm(-1) and semiconducting behavior with an activation energy of 170 meV. The paramagnetic susceptibility obeyed the Curie-Weiss law with a Curie constant of 4.42 emu K mol(-1) and a Weiss temperature of +3.4 K, and below 15 K, this short-range ferromagnetic interaction increasingly extended to two- and/or three-dimensional interactions, eventually giving rise to a ferromagnetic ordering, whose temperature (T-C) was determined to be 1.8 +/- 0.2 K using a resonant circuit method. The magnetic field dependence of magnetization showed that the saturation of magnetization was accomplished at ca. 60 kOe and the saturated value was ca. 5 mu(B), which is very close to the value obtained only due to Fe(III) (S = 5/2) d spins of one FeBr4- ion.