Dithiazolodithiazolyl Radicals: Substituent Effects on Solid State Structures and Properties

A general synthetic route to the pyridine-bridged dithiazolodithiazolyl framework R2BPR1, involving N-alkylation of a 4-substituted 2,6dichloropyridine, followed by amination and double Herz cyclization with S2Cl2, has been developed. The radicals R2BPMe (R2 = Me, Ph) have been prepared and characterized by EPR spectroscopy and cyclic voltammetry. Their crystal structures have been determined by X-ray crystallography. Both structures consist of undimerized slipped radical -stacks. Lateral interactions in MeBPMe (space group P21\c) generate chainlike arrays with radicals linked by inversion centers; there are no close interchain S-S contacts. By contrast, in PhBPMe (space group P3121) the radical -stacks are nested about 31 axes, so as to produce an extensive 2-dimensional network of intermolecular S-S interactions. Variable-temperature magnetic susceptibility measurements reveal that MeBPMe is essentially paramagnetic, whereas PhBPMe displays strong antiferromagnetic coupling. A value of J = 149 cm-1 has been estimated by using a Bonner-Fisher anti-ferromagnetic chain model. Pressed pellet conductivity measurements indicate values of RT 10-5 S cm-1 for both R2BPMe compounds (R2 = Me, Ph), suggesting Mott insulator ground states. The structural results and transport properties are discussed in the light of extended Hückel theory band structure calculations