Synthesis, crystal structures and photoluminescence of Zn–Ln heterometallic polymers based on pyridine-2,3-dicarboxylic acid

Three new two-dimensional 3d–4f isostructural heterometallic coordination polymers, namely [Ln2Zn(2,3-pydc)4(H2O)4·4H2O]n (Ln = Sm (1), Eu (2), Gd (3), 2,3-pydcH2 = pyridine-2,3-dicarboxylic acid) have been successfully synthesized by the hydrothermal reactions of Ln2O3, Zn(NO3)2·6H2O, H2pydc and H2O. X-ray diffraction analyses reveal that they possess a 2D heterometallic framework containing 1D lanthanide chains based on dimeric [Ln(2,3-pydc)2(H2O)2]2 unit. The Zn(II) ion, which is six-coordinated by four oxygen and two nitrogen atoms from four 2,3-pydc2− ligands, as a bridge, links the lanthanide chains to make the 1D chains further extend into 2D layer framework. Furthermore, the neighboring layers are assembled into three-dimensional supramolecular network through inter-layer O–H⋯O and C–H⋯O hydrogen-bond interactions. In addition, the solid-state luminescent property of complex 2 was investigated.