Two Multi-Copper-Containing Heteropolyoxotungstates Constructed from the Lacunary Keggin Polyoxoanion and the High-Nuclear Spin Cluster

Two novel high-nuclear copper-substituted polyoxometalates, Na16[Cu14(OH)4(H2O)16(SiW8O31)4]·20.5H2O (1) and
K10Na14[Cu10(H2O)2(N3)4(GeW9O34)2(GeW8O31)2]·30H2O (2), containing 14 Cu2+ ions and 10 Cu2+ ions, respectively,
have been obtained in aqueous solution and characterized by IR, UV, TG, element analysis, electrochemistry, and
single-crystal X-ray analyses. The polyoxoanion framework of 1 is composed of four [β-SiW8O31] units connected
by 14 Cu2+ ions to constitute a tetrameric compound. In 2, two [β-GeW8O31] anions and two [B-α-GeW9O34] anions
are connected together by a [Cu10(N3)4O32(H2O)2] {Cu10(N3)4} cluster to construct a novel tetrameric compound.
The results of the electrocatalytic experiments reveal that the reduced species of 1 and 2 have electrocatalytic
activities for nitrate reduction.