Redox, magnetic, and structural properties of 1,3,2-dithiazolyl radicals. A case study on the ternary heterocycle S3N5C4

by Barclay, T. M.; Cordes, A. W.; George, N. A.; Haddon, R. C.; Itkis, M. E.; Mashuta, M. S.; Oakley, R. T.; Patenaude, G. W.; Reed, R. W.; Richardson, J. F.; Zhang, H.

The characterization of the heterocyclic radical 1,2,5-thiadiazolo[3,4-b]-1,3,2-dithiazolo[3,4-b]pyrazin-2-yl (TDP-DTA) is described. The compound is prepared by treatment of 5,6-dithiolo-1,2,5-thiadiazolo[3,4-b]pyrazine with S3N3Cl3 and purified by fractional sublimation in vacuo. The results of cyclic voltammetry and ESR analysis of TDP-DTA and related heterocyclic dithiazolyls indicate that the spin distributions and donor/acceptor properties of these radicals are extremely sensitive to the nature of the 4,5-substituents. The crystal structure of TDP-DTA has been determined at two temperatures. At 293 K, the crystals are triclinic, space group P (1) over bar, with a = 4.4456(8), b = 8.407(2), c = 9.671(3) Angstrom, alpha = 71.34(2), beta = 89.28(2), gamma = 87.80(2)degrees, Z = 2 (for C4N5S3); at 150 K the crystals are triclinic, space group P (1) over bar, with a = 7.489(7), b = 9.593(4), c = 10.759(6) Angstrom, alpha = 65.77(4), beta = 74.10(6), gamma = 74.64(6)degrees, Z = 2 (for C8N10S6). At 293 K the structure consists of ribbons of TDP-DTA radicals packed in a slipped pi-stack arrangement. In the low temperature phase alternate layers of ribbons are shifted laterally to produce arrays of dimers. Within these dimers three long (3.401(5), 3.460(5) and 3.511(5) Angstrom) interannular S-S contacts link the two molecules. A multiple "tectonic plate" slippage mechanism is proposed to account for the interconversion of the two phases. The structural results are discussed in the light of variable temperature magnetic susceptibility measurements.

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