Heterocycle-Substituted Stable Thioaminyl Radicals: Isolation, ESR Spectra, and Magnetic Properties1

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Abstract
N-[(2-Benzothiazolyl)thio]- (1), N-[(2-benzoxazolyl)thio]- (2), and N-(2-pyrimidylthio)-2,4,6-trisubstituted-phenylaminyls (3) were generated by oxidation of the corresponding amines. Although 2 and 3 were not sufficiently persistent to be isolated, 1 was very persistent and could be isolated as radical crystals. The ESR spectra of nondeuterated and partially deuterated 1 − 3 radicals were measured, and the spin density distributions were estimated from the hyperfine coupling constants. Ab initio molecular orbital calculations were made for 1 to discuss the spin density distribution in more detail. Single-crystal X-ray crystallographic analysis was performed for one radical. Magnetic properties were measured for isolated four radicals with a SQUID. Two radicals showed ferromagnetic interaction, and analyses of χT vs T plots with the one-dimensional regular Heisenberg model gave 2J/kB = 5.8 and 8.6 K. The remaining two radicals showed antiferromagnetic interaction. Analyses of the χT vs T plots with the Curie−Weiss law or dimer model gave θ = −1.4 K and 2J/kB = −1370 K. The strong antiferromagnetic interaction could be explained in terms of the X-ray crystallographic results.