The Proof of a Triplet Ground State in the N,N′-Di-t-butyl-m-phenylenebinitroxide Biradical

The magnetic susceptibility of the N,N′-di-t-butyl-m-phenylenebinitroxide biradical has been measured in the temperature range from 60 to 300 K. The susceptibility follows the Curie-Weiss law, with a paramagnetic Curie constant of 0.90±0.04 K·-emu/mol and a Weiss constant of −19±2 K. This susceptibility suggests that the ground state of the biradical is a triplet and that an intramolecular pure triplet approximation, 2J>>kT, is reliable in the temperature region below 300 K. The negative Weiss constant is due to the negative exchange interaction, J′<0, between the triplets.