Solvent-controlled 3D lanthanide-polyoxometalate frameworks: Reduction and stabilization of Ag nanocomposites and catalytic properties

Four three-dimensional lanthanide-polyoxometalate complexes, [K ₄Ln₃(H₂IDC)₃(HIDC) ₃(H₂O)₃(SiW₁₂O₄₀)] ·nH₂O (Ln = La (1), n = 7 and Ce (2), n = 6; H₃IDC = 4,5-imidazoledicarboxylic acid) and [Ln₄(HIDC)₄(H ₂O)₈(SiW₁₂O₄₀)]·11H ₂O (Ln = La (3) and Ce (4)), have been synthesized by solvothermal reactions. Compounds 1 and 2 are 3D architectures that include 2D layered structures connected by K⁺ cations, which were realized by tuning the reaction media with different ratios of water and ethanol. By comparison, in the cases of 3 and 4, lanthanide ions coordinate to tridentate HIDC ligands forming 2D Ln-organic networks, which are further pillared by α-Keggin type [SiW₁₂O₄₀]^4- polyoxoanions and thus constructing new 3D frameworks featuring 1D channels along the a and b axes. All of these complexes could induce the formation of Ag nanocomposites possessing high catalytic activity towards the reduction of 4-nitrophenol (4-NP) in the presence of NaBH₄.