A new bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)-based salt with a ferrocenyl moiety, alpha'''-(BEDT-TTF)(4)(Fe(C5H4SO3)(2))center dot 6H(2)O, has been prepared. The ferrocenyl part of this salt is neutral and diamagnetic, but the magnetic susceptibility is well modeled by a Curie-Weiss law with C = 0.142 emu center dot K center dot mol(-1) (approximate to 1/3 of S = 1/2 spin). The spin is likely to be localized on the donor layer because of its unique charge disproportionation.