Stable Iminonitroxide Biradical in the Triplet Ground State

Magnetic properties and crystal structure of a pyridine-substituted iminonitroxide biradical, 2,6-bis(4,4,5,5,-tetramethyl-4,5dihydro-1H-imidazol-2-yl-1-oxyl)pyridine (1), were examined. The molecular ground state of 1 was found to be triplet (S = 1) with a singlet–triplet energy gap of 7 K. The ground-state triplet biradical serves as a building block for molecule-based magnets of S > 1/2 based on intermolecular noncovalent bonding architecture.