Magnetic Properties of an Organic Biradical,m-BNN:m-Phenylene Bis(α -Nitronyl Nitroxide)

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Abstract
Magnetic properties of a stable organic biradical, meta-phenylene bis(α-nitronyl nitroxide) ( m -BNN), have been studied. The molecular ground state is found to be triplet ( S =1) by the solution EPR measurements. An X-ray structure analysis reveals that m -BNN crystallizes in a dimeric fashion. Susceptibility of a m -BNN single crystal exhibits anomalous temperature dependence as a result of intermolecular exchange interactions. From an analysis based on the structure of magnetic energy spectrum, unusual gap formation in the m -BNN crystals is deduced. The origin of the gaps is discussed in the light of the peculiarity of Heisenberg integer spins.