Diamagnetic Precursor to Biradical by Means of a Thermal Trigger: A Head-to-Tail (N-O)2 Four-Membered Ring Formed in Naphthalene-1,8-diyl Bis(tert-butyl Nitroxide).

Abstract

The title compound was synthesized, and ESR and magnetic analysis revealed diamagnetic properties below 400 K. The crystal structure analysis clarified that the molecule possesses an approximate C2 symmetry with a head-to-tail (N-O)2 four-membered ring. The N···O distances are 2.349(4) - 2.374(4) Å, belonging to the class found in diamagnetic phases of dimerized nitroxide materials. A zero-field splitting pattern appeared in the solid-state ESR around 440 K on heating. The density functional theory (DFT) calculations supported the formation of a biradical.