Polyoxoniobates with the long-sought feature of face-sharing octahedra stabilized by Te(iv): a synthetic analogue of natural minerals

Polyoxometalates (POMs) are primarily constructed from {MO₆} octahedra connected through corner-, edge-, and/or face-sharing modes, with face-sharing being particularly rare. Silverton clusters, characterized by their face-sharing {MO₆} octahedra, have been reported for Mo and W. However, Nb-based Silverton and polyoxoniobates (PONbs) with face-sharing octahedra have not yet been synthesized, despite their occurrence in natural minerals. Herein, [(Nb₁₃O₄₂){Te₃(B-α-TeNb₉O₃₃)}₄] (1a) and its trivacant structure [(Nb₁₀O₃₆){Te₃(B-α-TeNb₉O₃₃)}₄] (2a) with the long-sought feature of face-sharing {NbO₆} octahedra have been synthesized for the first time. In 1a, the central {Nb₁₃O₄₂}, consisting of six sets of face-sharing {Nb₂O₉} and a central Nb, is surrounded by 12 Te(iv) ions anchored on four {TeNb₉O₃₃}. Notably, the observed {Nb₁₃O₄₂} can be viewed as both a synthetic analogue of natural minerals and a topological isomer of the classic Silverton cluster. Moreover, small angle X-ray scattering data analysis confirms the formation of the targeted PONb cluster and determines the co-existing key cluster species and their proportion during the assembly or disassembly process. Further computational studies indicate that highly charged Te(iv) ions play a key role in the stabilization of face-sharing PONbs. The photocatalytic hydrogen evolution activity of 1 has also been investigated. This work not only bridges the gap between natural and synthetic PONbs, but also deepens our understanding of the formation of face-sharing octahedra.