High-Field Electron Spin Resonance Study of a Nitroxide Biradical, 1,4-Bis(4‘,4‘-dimethyloxazolidin-N-oxyl)cyclohexane

Abstract

1,4-Bis(4‘,4‘-dimethyloxazolidine-N-oxyl)cyclohexane (1), a “fast exchange” biradical in which the principal directions of the g and D tensor are different, has been studied by ESR at low temperature at 245 and 294 GHz. These frequencies correspond to an “intermediate high field” (δgμBB ≈ |D|), i.e., such that the powder spectrum is neither dominated by the anisotropy of the g tensor (as at “very high field”) nor by that of the dipolar D tensor (as at “low field”). As B increases from low field to very high field, the canonical directions do not simply rotate from the principal directions of D to those of g but split into “pseudocanonical directions” at intermediate fields. The principal values of the magnetic tensors and their relative orientations were obtained by computer simulation. They are more accurate for the g tensor than those determined at low field; the dipolar parameter D is negative. Magnetization and ESR studies show that 1 is a ground-state singlet with an exchange interaction 2J/k = −25 ±...