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

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.

Stereoisomeric coordination polymers based on facial and meridional six-coordinate dysprosium(III ).

Due to the small differences in the chemical properties of facial (fac) and meridional (mer) stereoisomers, selective synthesis of one of the isomers is challenging, especially for lanthanide complexes. By using a flexible bidentate phosphine oxide ligand, we managed to isolate three stereoisomeric 2D and 3D coordination polymers, in which six-coordinate Dy(III) ions possess fac- or mer-Cl3O3 coordination environments. Structural studies indicate that the stereochemistry differences result from their various supramolecular interactions (e.g., hydrogen bonding and π⋯π stacking). Magnetic property measurements reveal the different static and dynamic magnetic behaviours of the three stereoisomers. Ab initio CASSCF calculations were then performed which indicated that their distinct magnetic behaviours arise from their fac/mer configurations. Compared to fac-Dy(III), mer-Dy(III) possesses more axial ground-state KDs and higher first excited KDs.