ESR and ENDOR Investigations of Spin Exchange in Mixed Galvinoxyl/Nitroxide Biradicals. Syntheses

Article abstract of DOI:10.1021/ja00378a013

The synthesis of a variety of mixed biradicals consisting of galvinoxyl and nitroxide moieties is given.For the first time successful fluid solution ENDOR experiments on mixed biradicals could be performed.The magnetic properties of these systems are significantly dependent (a) on the relative magnitudes of the exchange integral J as compared to the hyperfine interactions, (b) on the sign of J, and (c) on the difference of the g values of the constituent monoradical fragments.It is demonstrated that the ENDOR technique allows direct determination of the hyperfine coupling constants even in cases where is comparable in magnitude to the hyperfine coupling constants.Moreover, the sign of the exchange integral can be deduced from these measurements.It is shown that the ENDOR spectroscopy in combination with spin labeling to obtain "weakly coupled biradicals" may serve as a technique to measure signs of hyperfine coupling constants.