Polyoxometalate-based organic - Inorganic hybrid compounds containing transition metal mixed-organic-ligand complexes of N-containing and pyridinecarboxylate ligands

Five new organic-inorganic hybrid compounds based on the Keggin-type polyoxoanion [SiW₁₂O₄₀]^4-, namely [Cu₃(2,2′-bpy)₃(inic)(μ₂-OH)(H₂O)][SiW₁₂O₄₀]·2H₂O (1), [Cu₆(phen)₆(μ₃-Cl)₂(μ₂-Cl)₂Cl₂(inic)₂][SiW₁₂O₄₀]·6H₂O (2), [Cu₂(hnic)(2,2′-bpy)₂Cl]₂[H₂SiW₁₂O₄₀] (3), [Cu₂(nic)(phen)₂Cl₂]₂[SiW₁₂O₄₀] (4) and [Cu₂(pic)(2,2′-bpy)₂Cl]₂[SiW₁₂O₄₀] (5) (inic = isonicotinic acid, hnic = 2-hydroxy-nicotinic acid, nic = nicotinic acid, pic = picolinic acid, 2,2′-bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) have been synthesized and characterized by IR, UV-Vis, XPS, XRD, cyclic voltammetric measurements, photoluminescence analysis and single crystal X-ray diffraction analysis. Crystal analysis reveals that compound 1 exhibits a 2-D double layered framework structure constructed from [SiW₁₂O₄₀]^4- and copper-aqua-2,2′-bipy-hydroxyl-isonicotinate complexes. Compound 2 is a 0-D discrete structure formed by [SiW₁₂O₄₀]^4- and copper-chloro-isonicotinate-phenanthroline complexes. Compound 3 shows a 1-D single chain structure based on the linkage of copper-2,2-bpy-chloro-2-hydroxy-nicotinate complexes and [SiW₁₂O₄₀]^4-. Compounds 4 and 5 both contain polyoxometalate supported transition metal complexes, one is a polyoxometalate supported copper-chloro-nicotinate-phenanthroline complex in 4, and the other is a polyoxometalate supported copper-2,2-bpy-chloro-nicotinate complex in 5. It should be noted that nicotinic, isonicotinic and picolinic acids are structural isomers and 2-hydroxy-nicotinic acid is an in situ hydroxylated product of nicotinic acid. In addition, photocatalytic degradation of Rhodamine B (RhB) by compounds 1-5 has been investigated in aqueous solutions.