An electron spin resonance, ENDOR, and TRIPLE resonance study of symmetrical N,N′-disubstituted-4,4′-bipyridylium radical cations in which the quaternising groups are nitrogen heterocycles

Abstract

The e.s.r., ENDOR, and TRIPLE resonance results are reported for a novel series of symmetrical N,N′-diaryl-4,4′-bipyridylium radical cations in which the aryl groups are nitrogen heterocycles (pyridyls, pyrimidinyl, and pyrazinyl). A comparison is made between these systems and the previously reported fluorine- and methyl-substituted N,N′-diphenyl-4,4′-bipyridylium radical cations. Evidence is presented to suggest that steric hindrance in the N,N′-bis-(1-methyl-2-pyridyl) radical cation brings about a loss of ring planarity.