Organic-inorganic hybrid assemblies based on Ti-substituted polyoxometalates for photocatalytic dye degradation

Two new organic-inorganic hybrid compounds, [N(CH3)(4)](6)[Cu(II)Lo][(Ti2O)(PW11O39)(2)]center dot 4H(2)O (1) and [N(CH3)(4)](2)[H(2)bpp](2)[Cu(II)Lo][(Ti2O)(PW11O39)(2)]center dot 1.5H(2)O (2) (Lo = 1,2-bis(3-(2-pyridyl) pyrazole-1-ylmethyl)benzene, bpp = 1,3-bis(4-piperidyl)propane), based on Ti-substituted polyoxometalates (abbr. Ti-POMs) and the metal-organic linking units constructed by Cu-II ions and bichelate-bridging ligands (Lo), have been hydrothermally prepared. The two compounds were characterized by elemental analyses, IR spectra, TG analyses, XPS spectra, powder X-ray diffraction and single-crystal X-ray diffraction analyses. Both compounds contain a rare corner-sharing double-Keggin type POM architecture in the Ti-POM species. In 1 and 2, the double-Keggin-type polyoxoanions connect with the butterfly-type [Cu(II)Lo] units to form a 1-D chain and a square plane, respectively. The photocatalytic properties of compounds 1 and 2 were investigated with the methylene blue (MB) degradation model under UV irradiation, indicating good photocatalytic activity. Furthermore, to compare the photocatalytic properties of the Keggin-type Ti-POMs with those of traditional Keggin-type POMs, another compound [Cu(I)Lo](4)[PW12O40] (3) was synthesized by combining typical Keggin-type polyoxoanions with the metal-organic [Cu(I)Lo] units. A series of MB degradation experiments suggest that the Ti-POMs exhibit better photocatalytic activity than typical Keggin-type saturated POM species.