Tuning the structures based on polyoxometalates from 1-D to 2-D by using different secondary organic ligands

Abstract

Six new organic–inorganic hybrid compounds based on [XM₁₂O₄₀]⁴⁻ (X = heteroatom, M = metal atom), namely [Cu(pic)₂][H₂XM₁₂O₄₀]·2Hapy·2apy (X = Si, M = W for 1, X = Ge, M = W for 2 and X = Si, M = Mo for 3), [Cu(2,2′-bpy)₂][Cu(2,2′-bpy)(H₂O)][Cu(pic)₂]_0.5[XM₁₂O₄₀]·nH₂O (X = Si, M = Mo, n = 0.5 for 4, X = Ge, M = W, n = 1 for 5) and [Cu(phen)(H₂O)]₂[Cu(pic)₂][GeW₁₂O₄₀]·2.5H₂O (6) (pic = deprotonated picolinic acid, apy = 2-aminopyridine, 2,2′-bpy = 2,2′-bipyridine, phen = phenanthroline), have been synthesized and characterized by IR, UV-Vis, XRD, cyclic voltammetric measurements and single crystal X-ray diffraction analysis. Single crystal X-ray analysis reveals that compounds 1–3 are isomorphous and isostructural, in which each is based on [H₂XM₁₂O₄₀]²⁻ and [Cu(pic)₂]. Compounds 4 and 5 are also isomorphous and isostructural, of which the structures are more interesting than those of compounds 1–3. Both structures are constructed from [XM₁₂O₄₀]⁴⁻ and metal mixed–organic–ligand complexes. Compound 6 is also constructed from Keggin ions and metal mixed–organic–ligand complexes, which are, however, thoroughly different from those of compounds 4 and 5. The photodegradation properties of compounds 1–6 have been analyzed. Compounds 1–3 also exhibit rapid absorption properties for RhB (Rhodamine B). Detailed analysis of the photodegradation properties of compounds 1–5 reveals that the molybdate POM has stronger degradation ability for RhB than the tungstate one.