Nitronyl nitroxide triradical as a model compound for generalized ferrimagnetism

A novel nitronyl nitroxide triradical, p-triNN (1), has been synthesized, in which a π-conjugated biradical with a singlet ground state and a doublet monoradical are united by σ-bonds. Two kinds of intramolecular exchange interactions, one between the biradical and monoradical entities J(σ) through the σ-bonds and the other within the biradical moiety J(π) through the π-conjugation, were examined by paramagnetic susceptibility χm for the sample dispersed in an organic polymer film. The magnitude of J(σ) (2J(σ)/kB ≤ −0.01 K) was found to be much weaker than that of J(π) (2J(π)/kB = −70.0 K). This result indicates that the triradical p-triNN (1) can be used as a building block for generalized ferrimagnets, which from theoretical calculations have been predicted to exhibit an exotic spin alignment.