A Mesoionic Platform for Persistent Anionic Nitrogen-Centered Radicals.

Persistent anionic N-centered radicals are exceptionally rare, as the coexistence of negative charge and unpaired electron density typically promotes protonation, aggregation, and irreversible redox chemistry. Here we introduce mesoionic 1,2,3-triazines as a platform for stabilizing such elusive open-shell anions. These compounds undergo clean and reversible one-electron reduction to generate negatively charged nitrogen-centered radicals, and suitable substitution enables their isolation as crystalline salts. EPR spectroscopy, single-crystal x-ray diffraction, and computational analysis reveal dominant nitrogen spin localization together with reduction-induced structural changes consistent with occupation of a parent triazine antibonding orbital. The resulting anionic radicals display chemically clean electron-transfer behavior and are reversibly oxidized to their zwitterionic precursors. These findings further highlight the potential of mesoionic 1,2,3-triazines as redox-active molecular platforms for applications in complex electrochemical environments.