Three new polyoxoniobates constructed from Lindqvist-type hexaniobate and copper–amine complexes

Three new polyoxoniobates constructed from Lindqvist-type [Nb₆O₁₉]^8? and copper–amine complexes, [Cu(1,2-dap)₂]{[Cu(1,2-dap)₂]₂[Nb₆O₁₉H₂]}?·?10H₂O (1), [Cu(1,3-dap)₂]₂{[Cu(1,3-dap)]₂[Nb₆O₁₉]}?·?10H₂O (2), and [Cu(en)₂]_0.5{[Cu(en)₂]₂[Nb₆O₁₉H₃]}?·?12H₂O (3) (1,2-dap?=?1,2-diaminopropane, 1,3-dap?=?1,3-diaminopropane, and en?=?ethylenediamine), have been synthesized and characterized by elemental analyses, infrared, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectrum, and single-crystal X-ray diffraction. Compounds 1–3 exhibit bisupporting hexaniobate cluster structure, each with a [Nb₆O₁₉]^8? cluster decorated by two copper–amine complexes. In 1, adjacent bisupporting clusters are connected with one [Cu(1,2-dap)₂]²⁺ fragment via Cu?···?O weak interactions to generate a 1-D supramolecular chain structure. In contrast to 1, each bisupporting cluster in 2 is linked to another four neighboring ones through four [Cu(1,3-dap)₂]²⁺ fragments by Cu?···?O weak interactions to yield a 2-D supramolecular network. Different from 1 and 2, no detected interaction was found between bisupporting cluster and [Cu(en)₂]²⁺ in 3, the [Cu(en)₂]²⁺ fragment merely acts as an isolated countercation.     

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

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 {Co₁₂Nb₃₈O₁₃₂}, 54-nuclearity {Co₂₀Nb₃₄O₁₂₈}, 62-nuclearity {Co₂₆Nb₃₆O₁₄₀} and 87-nuclearity {Co₃₃Nb₅₄O₁₈₈}. 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 Co³⁺/Co²⁺ states as the different sized Co−O moieties of the bulk cubic-spinel Co₃O₄, suggesting that they can serve as various molecular models of the cubic-spinel Co₃O₄. 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 CO₂ reduction.