Synthesis And Structure Of Lanthanide Complexes Based On Keggin-type Polyoxometalates And Their Photocatalytic Oxidation Of Thiophene

Polyoxometalates, with nanoscale and the diversity for coordination, show greatadvantage in the formation of coordination polymers. In this paper, six unreported lanthanidecomplexes have been hydrothermally synthesized with H₂pdc and Keggin-typepolyoxometallates. They have been characterized by elemental analysis, IR, TG, PXRD andX-ray single crystal diffraction. Besides, their photocatalytic oxidation of thiophene has alsoinvestigated.Five [BW₁₂O₄₀]^5-or [PMo₁₁VO₄₀]_<sup>4--containing MOF compounds have beenhydrothermally synthesized:{K[La（H₂O）₄（pdc）]₄}[BW₁₂O₄₀]·2H₂O1{K[Ce（H₂O）₄（pdc）]₄}[BW₁₂O₄₀]·2H₂O2{K[Tb（H₂O）₃（pdc）]₄}[BW₁₂O₄₀]·6H₂O3{K[Dy（H₂O）₃（pdc）]₄}[BW₁₂O₄₀]·6H₂O4{K[Er（H₂O）₃（pdc）]₄}[BW₁₂O₄₀]·6H₂O5[Ce（H₂O）₄（pdc）]₄[PMo₁₁VO₄₀]·2H₂O61,2and6are isostructural, and3,4and5are also isostructural. Ln³⁺are coordinatedwith H₂pdc to form a3D [Ln（H₂O）₄（pdc）]⁺cationic framework which showing a zeolite-likeGIS topological structure.[BW₁₂O₄₀]^5-anions and K⁺ions are arrayed in nonuniform channelsof the structure in a zigzag fashion. In the structures of1,2and6, K⁺ions show an octahedralconfiguration which bind [BW₁₂O₄₀]^5-anions forming a1D chain viewed form b axis. Thefour equatorial positions are occupied by four oxygen atoms of carboxyl groups and the twoaxial positions are occupied by two terminal oxygen atoms of [BW₁₂O₄₀]^5-anions.In the structures of3,4and5, Tb³⁺, Dy³⁺and Er³⁺ions exhibit a lower coordinationnumber because of the effect of lanthanide contraction. The metal ions only connect withthree coordinated water molecules. K⁺ions also show a six-coordinated environment. Thefour equatorial positions are occupied by four oxygen atoms of carboxyl groups and two axialpositions are occupied by two water molecules.In addition,1-5have been used as catalysts to oxidize thiophene under UV light with theoxidant of O2. Thiophene could be well oxidized catalytically. The conversion to oxidize thiophene on2is ca.97%in12hours. The mechanism of photocatalytic oxidation ofthiophene and the final photoproduct have been investigated.