Tetrahedral Polyoxometalate Nanoclusters with Tetrameric Rare-Earth Cores and Germanotungstate Vertexes

Two novel 1D copper-bridged tetrahedral polyoxometalate nanoclusters with tetrameric rare-earth cores and germanotungstate vertexes, Na₃H₇­[Cu­(en)₂]₅­[Cu­(en)₂­(H₂O)]₂­[RE₄Ge₄­W₄₆O₁₆₄­(H₂O)₃]·<i>n</i>H₂O (RE = Gd^III, <i>n</i> = 25 for <b>1</b>; RE = Y^III, <i>n</i> = 23 for <b>2</b>; en = ethylenediamine), have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectra, thermogravimetric analysis (TGA), and single-crystal X-ray diffraction. The most prominent structural feature of <b>1</b> and <b>2</b> consists of unprecedented tetrahedral RE-substituted germanotungstate nanoclusters {[(α-Ge­W₁₁O₃₉­RE)₂­(μ₃-WO₄)­(α-Ge­W₁₁O₃₉­RE­(H₂O))]­(μ₄-WO₄)­[α-Ge­W₁₁O₃₉­RE­(H₂O)₂]}^24–, in which four mono-RE^III-substituted Keggin [α-Ge­W₁₁O₃₉­RE­(H₂O)_<i>n</i>]^5– (<i>n</i> = 0, 1, 2) moieties are combined together with the aid of two WO₄^2– connectors. What’s more interesting is that adjacent tetrahedral nanoclusters are interconnected with each other via [Cu­(en)₂]²⁺ bridges, forming a 1D extended chain architecture. To our knowledge, <b>1</b> and <b>2</b> are the first polyoxometalate-based Cu–RE containing 1D chain constructed from tetrahedral RE-substituted germanotungstate nanoclusters and copper–organic bridges. Furthermore, the solid-state electrochemical and electrocatalytic properties of <b>1</b> and <b>2</b> have been carried out in 0.5 mol·L^–1 Na₂SO₄ + H₂SO₄ aqueous solution by entrapping them in a carbon paste electrode. <b>1</b> and <b>2</b> display apparent electrocatalytic activities for the nitrite and bromate reduction