Semiquinone-Bridged Bisdithiazolyl Radicals as Neutral Radical Conductors

摘要

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·MeCN, both of which crystallize in the polar orthorhombic space group Pna2_1, revealed the importance of intermolecular oxygen-to-sulfur (CO…SN) interactions in generating rigid, tightly packed radical π-stacks, including the structural motif found for 3a-MeCN in which radicals in neighboring π-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·MeCN indicated high values of σ(300 K) (>10~(-3) S cm~(-1) with correspondingly low thermal activation energies E_(acv) reaching 0.11 Ev in the case of 3a·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·MeCN. The unsolvated material 3a orders as a spin-canted antiferromagnet at 8 K, with a canting angle φ = 0.14° and a coercive field H_c = 80 Oe at 2 K.