Synthesis and characterization of 0D–3D copper-containing tungstobismuthates obtained from the lacunary precursor Na$_9$[B-$\alpha$-BiW$_9$O$_{33}$]

The reaction of the lacunary polyoxometalate precursor Na$_9$[B-$\alpha$-BiW$_9$O$_{33}$]·19.5H$_2$O with Cu(II) ions was explored in search of new economic ways to copper tungstobismuthates as interesting prototypes for water oxidation and reduction catalysts. The emerging series of new 0D–3D polyoxometalate architectures with distinct copper cores was structurally characterized. Na$_6$Rb$_6$[Cu$_3$(H$_2$O)$_3$(BiW$_9$O$_{33}$)$_2$] (Cu-4) and 3D-K$_{6.56}$Cu$_{0.43}$H$_{2.20}$[(Cu$_3$Cl)(K$_{2.62}$Cu$_{0.38}$(H$_2$O)$_3$)(B-$\alpha$-BiW$_9$O$_{33}$)$_2$]·13H$_2$O (Cu-5) display a Cu$_3$(H$_2$O)$_3$ core. The 2D representatives Na$_{12}$[Cu$_2$(H$_2$O)$_4$Cl$_2$(BiW$_{10}$O$_{35}$)$_2$] (Cu-1a), Na$_{10}$[Cu$_2$(H$_2$O)$_6$(BiW$_{10}$O$_{35}$)$_2$] (Cu-1b), 2D-Na$_7$K$_3$Cu$_{0.5}$Cl[Cu$_2$(H$_2$O)$_4$(BiW$_{10}$O$_{35}$)$_2$] (Cu-2), and 2D-Na$_{5.5}$K$_{2.5}$Cu[Cu$_2$(H$_2$O)$_4$(BiW$_{10}$O$_{35}$)$_2$] (Cu-3) contain Cu$_2$(H$_2$O)$_n$W$_2$O$_4$ cores. Interestingly, the bismuth-free 1D paratungstate B Na$_4$K$_4$Cu[H$_2$W$_{12}$O$_{42}$] (Cu-6) is formed through reassembly of the precursor. Cu-5 displays a disordered transition metal core, implying the presence of the polyanions [Cu$_4$(H$_2$O)$_4$(BiW$_9$O$_{33}$)$_2$]$^{10}$– and [Cu$_5$(H$_2$O)$_5$(BiW$_9$O$_{33}$)$_2$]$^8$–. The magnetic properties of Cu-5 as well as its activity as visible-light-driven H$_2$ and O$_2$ evolution catalyst were evaluated