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 (Ω 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.