On–Off Switching of a Photocatalytic Overall Reaction through Dynamic Spin-State Transition in a Hofmann Clathrate System

Abstract

Spin-state transition is a vital factor that dominates catalytic processes, but unveiling its mechanism still faces the great challenge of the lack of catalyst model systems. Herein, we propose that the {Fe-Pt} Hofmann clathrates, whose dynamic spin-state transition of metal centers can be chemically manipulated through iodine treatment, can serve as model systems in the spin-related structural-catalytic relationship study. Taking the photocatalytic synthesis of H₂O₂ as the basic catalytic reaction, when the spin state of Fe(II) in the clathrate is high spin (HS), sacrificial agents are indispensable to the photosynthesis of H₂O₂ because only the photocatalytic oxygen reduction reaction (ORR) occurs; when it is low spin (LS), both the ORR and water oxidation reaction (WOR) can take place, enabling a high H₂O₂ photosynthesis rate of 66 000 μM g^-1 h^-1 under visible-light irradiation. In situ characterizations combined with density functional theory calculations confirmed that, compared with the HS-state counterpart, the LS state can induce strong charge transfer between the LS Fe(II) and the iodide-coordinating Pt(IV) in the polymer and reduce the energy barriers for both the ORR and WOR processes, dominating the on-off switching upon the photosynthesis of H₂O₂ in O₂-saturated water. What's more, the one-pot tandem reactions were conducted to utilize the synthesized H₂O₂ for transforming the low-value-added sodium alkenesulfonates into value-added bromohydrin products with decent conversion rates. This work provides a pioneering investigation into on-off switching the photocatalytic overall reaction through manipulating the metallic spin-state transition in spin-crossover systems.