Semiquinone-Bridged Bisdithiazolyl Radicals as Neutral Radical Conductors

Semiquinone-bridged bisdithiazolyls 3 represent a new class of resonance-stabilized neutral radical for use in the design of single-component conductive materials. As such, they display electrochemical cell potentials lower than those of related pyridine-bridged bisdithiazolyls, a finding which heralds a reduced on-site Coulomb repulsion U. Crystallographic characterization of the chloro-substituted derivative 3a and its acetonitrile solvate 3a center dot MeCN, both of which crystallize in the polar orthorhombic space group Pna2(1), revealed the importance of intermolecular oxygen-to-sulfur (CO center dot center dot center dot SN) interactions in generating rigid, tightly packed radical pi-stacks, including the structural motif found for 3a center dot MeCN in which radicals in neighboring pi-stacks are locked into slipped-ribbon-like arrays. This architecture gives rise to strong intra- and interstack overlap and hence a large electronic bandwidth W. Variable-temperature conductivity measurements on 3a and 3a center dot MeCN indicated high values of sigma(300 K) (>10(-3) S cm(-1)) with correspondingly low thermal activation energies E-act, reaching 0.11 eV in the case of 3a center dot MeCN. Overall, the strong performance of these materials as f = 1/2 conductors is attributed to a combination of low U and large W. Variable-temperature magnetic susceptibility measurements were performed on both 3a and 3a center dot MeCN. The unsolvated material 3a orders as a spincanted antiferromagnet at 8 K, with a canting angle phi = 0.14 degrees and a coercive field H-c = 80 Oe at 2 K.