Stepwise assembly and reversible structural transformation of ligated titanium coated bismuth-oxo cores: shell morphology engineering for enhanced chemical fixation of CO.

Herein, we report the stepwise assembly and reversible transformation of atomically precise ligated titanium coated bismuth-oxide core nanostructures. The soluble and stable BiO@Ti-oxo clusters with weakly coordinated surface salicylate ligands were first prepared as precursors. Owing to the high surface reactivity of the BiO inner core, its shell composition and morphology could be systemically modified by assembly with various Ti ions and auxiliary ligands (L), especially those with different flexibility, bridging ability and steric hindrance. As a result, a series of new core-shell BiO@Ti L-oxo ( = 14, 16, 18 or 20) clusters containing gradually increasing shell Ti atoms were successfully synthesized. Among them, the BiTi-oxo cluster is the largest one in the family of heterometallic Bi/Ti-oxo clusters to date. In addition, the sensitized titanium outer shell can effectively improve the photocurrent response under visible light irradiation. More remarkably, the obtained core-shell BiO@Ti L-oxo clusters can serve as stable and efficient catalysts for CO cycloaddition with epoxides under ambient conditions, whose activity was significantly influenced by the outer ligated titanium shell structure. This work provides a new insight into the construction of atomically precise heterometallic core-shell nanostructures and also an interesting shell engineering strategy for tuning their physicochemical properties.