Prototypal dithiazolodithiazolyl radicals: Synthesis, structures, and transport properties

by Beer, Leanne; Britten, James F.; Brusso, Jaclyn L.; Cordes, A. Wallace; Haddon, Robert C.; Itkis, Mikhail E.; MacGregor, Douglas S.; Oakley, Richard T.; Reed, Robert W.; Robertson, Craig M.

New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolylium salts, based on double Herz condensations of N-alkylated 2,6-diaminopyridinium salts with sulfur monochloride, have been developed. The two prototypal 1,2,3-dithiazolo-1,2,3-dithiazolyl radicals HBPMe and HBPEt have been prepared and characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G**) gas-phase disproportionation enthalpies favor a low on-site Coulombic repulsion energy U in the solid state. The crystal structures of HBPR (R = Me, Et) have been determined by X-ray crystallography (at 293 K). Both consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S- - -S contacts. Magnetic, conductivity, and optical measurements have been perfomed and the results interpreted in light of extended Huckel band calculations. The crystalline materials are paramagnetic above 100 K, with room-temperature conductivities sigma(RT) Of 10(-5)-10(-6) S cm(-1); the slightly greater conductivity of the R = Et compound can be associated with a more well developed band structure. We suggest a Mott-Hubbard insulator ground state for these materials, with an on-site Coulomb repulsion energy U of about 1.0 eV.

Journal of the American Chemical Society
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1520-5126; 0002-7863