Mono- and dinitroxide radicals from 9,9′(10H,10′H)-spirobiacridine: An approach to a D2d triplet biradical

Oxidation of 9,9′(10H,10′H)-spirobiacridine with m-chloroperbenzoic acid gave a dinitroxide biradical derivative, SBDO, together with a monoradical, SBO. Their molecular and crystal structures were determined by X-ray crystallographic analysis. Magnetic measurements on a polycrystalline sample of SBDO revealed the presence of dominant antiferromagnetic interaction, which can be ascribed mainly to intermolecular interaction due to close contacts between two nitroxide groups. The intermolecular N–O distances were 3.176(2) and 3.184(2) Å. The diluted ESR experiments and the DFT calculation on a single molecule of SBDO indicated the ground triplet state. We also found that SBO worked as a versatile host for organic solvent molecules (CH2Cl2, CHCl3, CH3CN, ClC6H5, CH3OH, etc.).

Graphical abstractIs the ground state of a title biradical (SBDO) molecule triplet or singlet? The X-ray crystallographic analysis revealed the orthogonality between the two π-spin systems. Although the magnetic measurements on a polycrystalline sample of SBDO revealed the presence of antiferromagnetic interaction, the diluted ESR experiments and the DFT calculation on a single SBDO molecule indicated the ground triplet state.Figure optionsDownload full-size imageDownload as PowerPoint slide