Copper(II)–lanthanide(III) coordination polymers constructed from pyridine-2,5-dicarboxylic acid: Preparation, crystal structure and photoluminescence

A series of 3d–4f heterometallic coordination polymers, formulated as {[Cu3Ln2(pydc)6(H2O)12]·4H2O}n [Ln=Tb (1), Eu (2), Dy (3), Ho (4), Lu (5)], {[CuNd2(pydc)4(H2O)3]·H2O}n (6) and {[Cu3Pr2(pydc)6(H2O)13]·4H2O}n (7) (where H2pydc=pyridine-2,5-dicarboxylic acid), have been hydrothermally prepared by reactions of H2pydc ligand with lanthanide ions in the presence of Cu(II) ion. X-ray crystal structure analysis reveals that these compounds exhibit rich structural chemistry. 1–5 are isomorphous and present a two-dimensional network constructed from Ln2Cu2L2(H2O)2 SBU rings and CuL2(H2O) building blocks. In 6, two-dimensional ladder-like layers based on Nd(III) belts and CuL2O2 units are assembled by H2pydc ligands into a three-dimensional open framework. Polymer 7 displays a two-dimensional wave-like layer structure containing two distinct ring units, in which a new coordination mode of the pydc2− ligand is observed. The results indicate that the coordination flexibility of the pydc2− ligand and lanthanide contraction effect play cooperative roles in the formation of coordination polymers with different polymeric architectures. Compounds 1–2 exhibit intense green and red luminescence emission characteristics of Tb(III) and Eu(III), respectively. Furthermore, elemental analyses (EA), infrared spectra (IR) and thermogravimetric analyses (TGA) of these compounds were also studied.

Graphical abstractSeven 3d–4f heterometallic coordination polymers were synthesized by reactions of H2pydc with lanthanide metal ions in the presence of Cu2+, the effects of Cu2+ on the structures and photoluminescent properties of Ln–pydc2− systems were investigated .Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Seven 3d–4f heterometallic compounds have been prepared and characterized. ► 1–5 and 7 are constructed from Ln2Cu2L2(H2O)2 rings and CuL2(H2O) building blocks. ► One new coordination mode of the pydc2− ligand is first observed. ► 1–2 exhibit intense characteristic luminescence emission spectra of lanthanide ions.