A Bimodal Oxobenzene-bridged Bisdithiazolyl Radical Conductor

The preparation and structural characterization of the methyl-substituted oxobenzene-bridged bisdithiazolyl radical 3b is described. Crystals of 3b belong to the monoclinic space group C2/c and contain two distinct radical environments, A and B. There are eight A radicals in the unit cell, which occupy general positions and form alternating twisted pi-stacks running parallel to the c-axis. The four B radicals also adopt an alternating pi-stack pattern, but each molecule lies on a crystallographic 2-fold rotation axis, and the overlay of neighboring radicals is centrosymmetric. Stacks of A radicals are linked by close intermolecular S center dot center dot center dot O' and S center dot center dot center dot N' contacts into ribbon-like arrays that weave along the y-direction, and the B radical stacks are located in columnar cavities generated by the out-of-register alignment of the ribbons of A radicals. Variable temperature magnetic susceptibility measurements indicate a strongly antiferromagnetically coupled system, a result in accord with DFT estimated exchange energies for intrastack radical radical interactions. Four-probe conductivity measurements indicate a conductivity sigma(300 K) = 9.0 X 10(-4) S cm(-1), with a thermal activation energy E-act = 0.13 eV.