Metal(II)-Directed Various Polyoxometalates-Based Hybrid Compounds: Assembly, Structures and Properties

Three new polyoxometalates (POMs)-based hybrid compounds: H6[Cu(C5H5N2)2(Mo8O27)(H2O)2]·2(C5H6N2)·2H2O (1), H6[Co(C5H5N2)2(Mo8O27)(H2O)2]·2(C5H6N2)·2H2O (2) and H4[(C5H6N2)2{Ni(OH)6Mo6O18}]·4H2O (3) (C5H6N2 = 3-aminopyridine), have been synthesized by self-assembly of (NH4)6Mo7O24·4H2O, C5H6N2 and different metal nitrates at different pH values. The single crystal X-ray diffraction, IR spectra, PXRD and thermogravimetric analyses have been used to characterize the title compounds. Compounds 1 and 2 are isostructural 3D metal–organic frameworks with a CdSO4-type topology, which are constructed from infinite Mo8O276− inorganic chains in uncommon ABAB linking mode. Compound 3 exhibits a 1D supramolecular chain derived from in situ formed Anderson-type [Ni(OH)6Mo6O18]4− anions and 3-aminopyridine via hydrogen-bonding interactions. The structural diversities indicate that metal ions show great effect on the construction of different POMs and final architectures. The electrochemical behavior of compound 1, the photocatalytic activities of compounds 1–3 have been investigated in detail.