An Open-Shell Functionalization of Inorganic Benzene

A borazine derivative functionalized by nitroxide free radicals, N,N′,N″-(tris(4-Bromophenyl))-B,B′,B″-tris((2,6-dimethyl-4-(N-tert-butyl-N-oxyamino)phenyl) borazine (TriBNit), was synthesized as a milestone of open-shell inorganic benzene. The crystal structure determined from X-ray diffraction on a single crystal ascertains the grafting of three nitroxide radicals. The temperature dependence of the magnetic susceptibility evidences weak intramolecular antiferromagnetic interactions between the radicals with strong intermolecular antiferromagnetic interactions between two nitroxide moieties of two neighboring molecules. EPR spectroscopy at 80 K on a frozen glassy solution evidences the coexistence of S = 1/2 and S = 3/2 ground-spin state species. This is ascribed to the nitroxide radicals having different orientations with respect to the borazine core giving rise either to antiferromagnetic interaction with a low ground-spin state S = 1/2 or to ferromagnetic interaction with a high ground-spin state S = 3/2 as supported by theoretical data. At room temperature, because of nitroxide mobility, the EPR spectrum is averaged to a ground-spin state S = 1/2.