Crystallography and magnetism of 2-amido-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyls

Abstract Two 2-Ar-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl radicals were synthesized (Ar =  para -acetamidophenyl, and para -( tert -butyloxycarbonyl)aminophenyl, pAPNN , pBPNN ) that incorporate amide-type NH moieties as potential hydrogen bonding sites. Both form hydrogen bonded cyclic dyads, but pAPNN exhibits spin pairing (2 J / k  = (−)5 K) due to a close, antiparallel nitroxide-nitroxide stacking contact, while pBPNN is essentially paramagnetic.