Intermolecular magnetic interactions in 2,4,6-tri(tert-butyl)phenoxy and 2,6-di(tert-butyl)-4-tritylphenoxy radicals

Abstract

Variable temperature magnetic susceptibility and electron paramagnetic resonance studies of neat solid-state samples of 2,4,6-tri(tert-butyl)phenoxy radicals (3)and 2,6-di(tert-butyl)-4-tritylphenoxy radicals (4) showed antiferromagnetic coupling in both materials. Spin counts indicated appreciable dimerization of radical content in both species (up to ca. 70%) but the remaining spins in each sample were well described by a model of antiferromagnetically exchange-coupled Heisenberg S= 1/2 dimers. Antiferromagnetic behaviour was more pronounced in 3 than in 4, with exchange constants for these being ca.–7 and –1 K, respectively. There is evidence for substantial numbers of isolated radical spin sites in 3 but not in 4, with the Weiss constants for these being –2.4 and –0.85 K, respectively. The changes in behaviour from 3 to 4 are attributable to changes in the average inter-radical distance, induced by the large 4-trityl group in 4.