High-field electron spin resonance study of a nitroxide biradical, 1,4-bis(4',4'-dimethyloxazolidin-N-oxyl)cyclohexane

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'' (delta g mu B approximate to\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 +/- 2 K.