Diamagnetic Precursor\nto Biradical by Means of a Thermal\nTrigger: A Head-to-Tail (N–O)<sub>2</sub> Four-Membered Ring\nFormed in Naphthalene-1,8-diyl Bis(<i>tert</i>-butyl Nitroxide)

The title compound was synthesized, and ESR and magnetic\nanalysis\nrevealed diamagnetic properties below 400 K. The crystal structure\nanalysis clarified that the molecule possesses an approximate <i>C</i><sub>2</sub> symmetry with a head-to-tail (N–O)<sub>2</sub> four-membered ring. The N···O distances are\n2.349(4) – 2.374(4) Å, belonging to the class found in\ndiamagnetic phases of dimerized nitroxide materials. A zero-field\nsplitting pattern appeared in the solid-state ESR around 440 K on\nheating. The density functional theory (DFT) calculations supported\nthe formation of a biradical.