Four-Shell Polyoxometalates Featuring High-Nuclearity Ln26 Clusters: Structural Transformations of Nanoclusters into Frameworks Triggered by Transition-Metal Ions.

A series of polyoxometalates (POMs) that incorporate the highest-nuclearity Ln clusters that have been observed in such structures to date (Ln26  , Ln=La and Ce) are described, which exhibit giant multishell configurations (Ln⊂W6 ⊂Ln26 ⊂W100 ). Their structures are remarkably different from known giant POMs that feature multiple Ln ions. In particular, the incorporated Ln-O clusters with a nuclearity of 26 are significantly larger than known high-nuclearity (≤10) Ln-O clusters in POM chemistry. Furthermore, they also contain the largest number of La and Ce centers for any POM reported to date and represent a new kind of rare giant POMs with more than 100 W atoms. Interestingly, the La26 -containing POM can undergo a single-crystal to single-crystal structural transformation in the presence of various transition-metal ions, such as Cu2+ , Co2+ , and Ni2+ , from an inorganic molecular nanocluster into an inorganic-organic hybrid extended framework that is built from POM building blocks with even higher-nuclearity La28 clusters bridged by transition-metal complexes.