Ce-mediated molecular tailoring on gigantic polyoxometalate {Mo} into half-closed {CeMo} for high proton conduction.

Precise synthesis of polyoxometalates (POMs) is important for the fundamental understanding of the relationship between the structure and function of each building motif. However, it is a great challenge to realize the atomic-level tailoring of specific sites in POMs without altering the major framework. Herein, we report the case of Ce-mediated molecular tailoring on gigantic {Mo}, which has a closed structural motif involving a never seen {Mo} decamer. Such capped wheel {Mo} undergoes a quasi-isomerism with known {Mo} ball displaying different optical behaviors. Experiencing an 'Inner-On-Outer' binding process with the substituent of {Mo} reactive sites in {Mo}, the site-specific Ce ions drive the dissociation of {Mo} clipping sites and finally give rise to a predictable half-closed product {CeMo}. By virtue of the tailor-made open cavity, the {CeMo} achieves high proton conduction, nearly two orders of magnitude than that of {Mo}. This work offers a significant step toward the controllable assembly of POM clusters through a Ce-mediated molecular tailoring process for desirable properties.