Fine tuning of π-stack separation distances of semiquinone radicals affects their magnetic and electric properties

Two salts of tetrachloro- (chloranil, Cl4Q) and tetrabromosemiquinone (bromanil, Br4Q) radical anions with an organic cation N- methylpyridinium (N-MePy), displaying a variety of tunable electrical and magnetic properties, are characterized. These systems comprise π- stacks of equidistant semiquinone radical anions, without Peierls deformation and diamagnetic spin coupling. Both are stable up to 150 and 120°C in air, respectively, and are semiconductors with conductivities of 10-6 – 10-7 (Ohm cm)-1 in the single crystals. The room-temperature concomitant crystallization of two polymorphs with different magnetic properties (antiferromagnetic and Peierls- distorted diamagnetic) has been observed for Cl4Q∙N-MePy. The semiquinone radical organic salts represent a novel class of potential (multi)functional materials with tunable properties