Polyoxometalate-based entangled coordination networks induced by an extended bis(triazole) ligand

The introduction of an extended bridging bis(triazole) ligand, that is, 4,4'-bis(1,2,4-triazol-1-ylmethyl)biphenyl (BBPTZ), into the hydrothermal reaction system containing transition metal ions and Keggin-type polyoxometalates (POMs) led to the isolation of three new organic-inorganic hybrid entangled coordination networks, [Cu(I)2Cu(II)(BBPTZ)6][SiW12O40]⋅12H2O (1), [Ni(BBPTZ)2(H2O)][H2SiW12O40]⋅11H2O (2), and [Ni2(BBPTZ)4(H2O)2][SiW12O40]⋅3H2O (3). All three compounds were characterized by elemental analysis, IR spectroscopy, TG analysis, powder X-ray diffraction, and single-crystal X-ray diffraction. Compound 1 contains a 2-D POM-based metal-organic layer entangled with 1-D ladder-like metal-organic chains. The adjacent 2-D networks are parallel to each other, further stacking into a 3-D supramolecular framework with 1-D channels. Compound 2 exhibits a 1-D cantilever-type loop-containing chain. The Keggin-type POMs act as the cantilever groups, leading to the adjacent catilever-type chains interwaving together to form a 3-D supramolecular open framework with two types of channels. Compound 3 possesses a 3-D open framework based on 2-D metal-organic undulated layer and Keggin-type POM clusters. Three sets of such frameworks further interpenetrate with each other to form an interesting three-fold interpenetrating framework. The photocatalytic activities of compounds 1-3 for the decomposition of methylene blue (MB) under UV light have been investigated.