Construction of different dimensional inorganic-organic hybrid materials based on polyoxometalates and metal-organic units via changing metal ions: from non-covalent interactions to covalent connections

Five POM-based hybrid materials have been designed and synthesized based on different metal ions under hydrothermal conditions, namely, [Zn(Hfcz)(H2O)(3)](H(3)fcz)(SiMo12O40)center dot 3H(2)O (1), [Cd-2(Hfcz)(6)(H2O)(2)](SiMo12O40)center dot H2O (2), [Co-2(Hfcz)(2)(SiW12O40)](H(3)fcz)(2)(SiW12O40)center dot 10H(2)O (3), [Ni-2(Hfcz)(4)(H2O)(2)](SiW12O40)center dot 5H(2)O (4) and [Ag-4(Hfcz)(2)(SiMo12O40)] (5), where Hfcz is fluconazole [2-(2,4-difluorophenyl)-1,3-di(1H-1,2,4-triazol-1-yl)propan-2-ol]. Their crystal structures have been determined by X-ray diffraction, elemental analyses, IR spectra, and thermogravimetric analyses (TGA). There are 1D mono and double chain-like metal-organic units in compounds 1 and 2, respectively. Polyoxometalates and metal-organic units co-crystallize through hydrogen bonds. In compound 3, metal-organic sheets are pillared by one kind of polyanion through covalent connections to generate a sandwich double-sheet. The other kind of polyanion acts as a counter-ion and lies in two adjacent sandwich double-sheets through non-covalent interactions. Polyanions covalently link metal-organic sheets to extend to an unusual 3D 5-connected framework with the (4(4).6(6)) topology in 4. In compound 5, polyanions link metal-organic chains to form a sheet through covalent connections. It is interesting that compound 5 shows an intricate (4,5,10)-connected framework with (4(4).6(2))(4)(4(8).6(2))(2)(4(14).6(19).8(12)) topology based on two kinds of Ag cations as four-connected and five-connected nodes, and polyanions as ten-connected nodes, when Ag center dot center dot center dot O interactions are considered. It represents the highest connected network topology presently known for polyoxometalate systems. The structural differences among 1-5 indicate the importance of different metal-organic units, coordination modes of polyanions for framework formation, and the interactions between polyanions and metal-organic units. In addition, the luminescent properties of compounds 1, 2 and 5, and electrochemical behaviours of compounds 1-5 have been investigated.