Effect of lanthanide contraction on structures of 3D lanthanide organic frameworks from 5-nitroisophthalic acid and picolinic acid

Two different types of novel lanthanide coordination polymers constructed from 5-nitroisophthalic acid, and picolinic acid as auxiliary ligand, namely, {[Ln2(nip)2(pic)2(H2O)]}n (type I, Ln = Pr 1, Nd 2, Sm 3, Eu 4, and H2nip = 5-nitroisophthalic acid, Hpic = picolinic acid), and {[Ln4(nip)5(pic)2(H2O)2]·2H2O}n (type II, Ln = Tb 5, Dy 6, Ho 7, Er 8), have been hydrothermally synthesized and characterized by IR, elemental analysis, thermogravimetric analysis (TGA), single-crystal X-ray diffraction analyses and powder X-ray diffraction (PXRD). Complexes 1–4 (type I) are isostructural and the infinite 1D Sm-carboxylate chains are bridged by pia ligands to form 2D sheets, such sheets are further united together to generate a 3D supramolecular structure. Complexes 5–8 (type II) are isostructural and the infinite 1D Tb–carboxylate chains are bridged by pia ligands to form 2D sheets, such sheets are further united together to generate a 3D supramolecular structure. Furthermore, the luminescence properties of compounds 4 and 5 have also been studied.