From 1D to 3D lanthanide coordination polymers constructed with pyridine-3,5-dicarboxylic acid: synthesis, crystal structures, and catalytic properties

Abstract

Three series of lanthanide coordination polymers with formula [Ln₂(PDC)₃(H₂O)₂(DMF)]·4H₂O (type I) (Ln = La 1, Pr 2, Sm 3), [(CH₃)₂NH₂][Ln₂(PDC)₃(HCOO)(H₂O)₃]·2H₂O (type II) (Ln = Tb 4, Ho 5) and [Ln(HPDC)₃(H₂O)₂]·H₂O (type III) (Ln = Er 6, Lu 7) (H₂PDC = pyridine-3,5-dicarboxylic acid), have been successfully synthesized by the solvothermal reaction of pyridine-3,5-dicarboxylic acid (H₂PDC) with the corresponding lanthanide nitrate. Compounds 1–3 are isomorphous and all crystallize in triclinic space group P, showing a 3D microporous framework of pcu topology with square channels along the b-axis. Isostructural compounds 4 and 5 show the same 2D layer network of (4,4)-grid in the monoclinic P2₁/c space group. Isomorphic 6 and 7 crystallize in the monoclinic Cc space group and present 1D zigzag chains which expand to a 3D supramolecular structure through π⋯π stacking interactions. The structural diversity of these three classes of compounds may be attributed to the effect of lanthanide contraction. They were characterized by infrared spectra (IR), elemental analysis (EA), thermogravimetric analysis (TGA), powder X-ray diffraction (PXRD), and X-ray single crystal diffraction. Furthermore, the catalytic properties of these compounds were investigated and experiments revealed that compounds 1–3 show size-selective catalytic performance for cyanosilylation reactions and could be reused without losing their catalytic activity.