Core‐Shell‐Type All‐Inorganic Heterometallic Nanoclusters: Record High‐Nuclearity Cobalt Polyoxoniobates for Visible‐Light‐Driven Photocatalytic CO₂ Reduction

Abstract Only rarely have polyoxometalates been found to form core–shell nanoclusters. Here, we succeeded in isolating a series of rare giant and all‐inorganic core–shell cobalt polyoxoniobates (Co−PONbs) with diverse shapes, nuclearities and original topologies, including 50‐nuclearity {Co 12 Nb 38 O 132 }, 54‐nuclearity {Co 20 Nb 34 O 128 }, 62‐nuclearity {Co 26 Nb 36 O 140 } and 87‐nuclearity {Co 33 Nb 54 O 188 }. They are the largest Co−PONbs and also the polyoxometalates containing the greatest number of Co ions and the largest cobalt clusters known thus far. These molecular Co−PONbs have intriguing and atomically precise core–shell architectures comprising unique cobalt oxide cores and niobate oxide shells. In particular, the encapsulated cobalt oxide cores with different nuclearities have identical compositions, structures and mixed‐valence Co 3+ /Co 2+ states as the different sized Co−O moieties of the bulk cubic‐spinel Co 3 O 4 , suggesting that they can serve as various molecular models of the cubic‐spinel Co 3 O 4 . The successful construction of the series of the Co−PONbs reveals a feasible and versatile synthetic method for making rare core–shell heterometallic PONbs. Further, these new‐type core–shell bimetal species are promising cluster molecular catalysts for visible‐light‐driven CO 2 reduction.