Two new extended structures built from condensed Keggin-type polyoxotungstates and copper(II)-organic units

The reactions between trivacant Keggin polyanions and transition metal ions in the presence of organoamine resulted in the isolation of two new polyoxotungstates, that is, [Hen]₂[Cu(en)₂(H₂O)]₂{[Cu(en)₂]₂[X₂W₂₃CuO₇₉]}·4H₂O (X = Ge, 1; X = Si, 2; and en = 1,2-ethylenediamine). Single-crystal X-ray diffraction analyses reveal that the polyanions in 1 and 2 are constructed by saturated Keggin anions condensed through sharing common oxygen atoms into Keggin dimers, which are further fused by copper(II) bridging fragments into one-dimensional (1D) ladder-like chains and then extended to a 3D supramolecular framework through hydrogen bond interactions. The IR spectrum and X-ray powder diffraction have been studied in detail for compounds 1 and 2. The UV spectrum, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), the cyclic voltammetry and electrocatalytic activity toward the reduction of nitrite have also been studied for compound 1.