Identification of a Stable Zn^II–Oxyl Species Produced in an MFI Zeolite and Its Reversible Reactivity with O₂ at Room Temperature

Although a terminal oxyl species bound to certain metal ions is believed to be the intermediate for various oxidation reactions, such as O−O bond generation in photosystem II (PSII), such systems have not been characterized. Herein, we report a stable Zn^II–oxyl species induced by an MFI-type zeolite lattice and its reversible reactivity with O₂ at room temperature. Its intriguing characteristics were confirmed by in situ spectroscopic studies in combination with quantum-chemical calculations, namely analyses of the vibronic Franck–Condon progressions and the ESR signal features of both Zn^II–oxyl and Zn^II–ozonide species formed during this reversible process. Molecular orbital analyses revealed that the reversible reaction between a Zn^II–oxyl species and an O₂ molecule proceeds via a radical O–O coupling–decoupling mechanism; the unpaired electron of the oxyl species plays a pivotal role in the O−O bond generation process.