The syntheses, structures and characterizations of a series of frameworks constructed from polyoxometalates, metals and organic units

Abstract

Five hybrid compounds constructed from polyoxometalates, transition metals and organic ligands [Ni₂(4,4′-bpy)₅(H₂O)₂][HBW₁₂O₄₀]·5H₂O (1), [Ni₂(4,4′-bpy)₅(Cl)₂][H₂SiW₁₂O₄₀]·3H₂O (2), [Ni₂(4,4′-bpy)₅(Br)₂][H₂SiW₁₂O₄₀]·3H₂O (3), [SiW₁₂O₄₀]₃[Cu₂(4,4′-bpy)₇]·(H₂4,4′-bpy)₂·4H₃O·2H₂O (4) and [SiW₁₂O₄₀]₃[Cd₂(4,4′-bpy)₇]·(H₂4,4′-bpy)₂·4H₃O·2H₂O (5) have been prepared and characterized by IR, UV-vis, XPS, XRD, TG, circular dichroism, second order nonlinear optical (NLO) measurements, photoluminescent measurements and single crystal X-ray diffraction analyses. The X-ray diffraction analyses reveal that the five compounds all exhibit novel framework structures constructed from polyoxometalates, transition metals and organic ligands. The compounds 1, 2, and 3 are isomorphous and compounds 4 and 5 are isomorphous, too. There are two main differences among the first three compounds. The first difference of the three is the central atom of the Keggin ions: it is B atom for compound 1, and Si atom for compounds 2 and 3. The second difference of the three is the monodentate ligand coordinating to the Ni ions: it is water molecule for compound 1, chloride ion for compound 2 and bromide ion for compound 3. The difference between compounds 4 and 5 is the transition metal centre of the frameworks. In addition, compounds 4 and 5 are the first examples of compounds containing both Keggin ion and pseudo-Keggin ion.