Synthesis and structural characterizations of four polyoxometalate compounds consisting of transition metals or alkaline cations as the bridging units

Four new polyoxometalate compounds, namely [Cu2(pyrazine)4][Cu(pyrazine)2][PMo12O40] · 2H2O (1), {[K(H2O)2]4H8PW12O44}F · 8H2O (2), H9[K2KMo36O112(H2O)34] · 35H2O (3), and H3Na3[V10O28] · 15H2O (4), were prepared and characterized by single crystal X-ray diffraction, elemental analysis and IR spectroscopy. Single crystal X-ray diffraction analysis results reveal that, in compound 1, Keggin anion of [PMoO12O40]3− is enchased in the bowl-like Cu(I)–pyrazine intervals via weak interactions between terminal oxygen atoms and cations of Cu(I). For compound 2, a three-dimensional architecture with pores of 7.70 × 7.70 Å is constructed from the anions of [PW12O44]11− cross-linked via corner-sharing alkali cations of K+. The [Mo36O112(H2O)16]12− units of compound 3 are linked to form one wave-like chain via cations of K+. Whereas, in compound 4, anions of [V10O28]3− are linked via NaO6 octahedra to form two-dimensional layer structure. On the basis of this two-dimensional layer, a three-dimensional architecture is further formed via hydrogen bonds involving edge-shared NaO6 double octahedron.