Syntheses, structures and luminescent properties of a series of Ln(III) coordination polymers

Seven coordination polymers having the general formula {[Ln2(2,6-pydc)(ox)2⋅(H2O)4]⋅3H2O}n (Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6, Er 7; 2,6-pydc2− = 2,6-pyridinedicarboxylate, ox2− = oxalate) were synthesized by the hydrothermal method. Their IR, UV-Vis-NIR absorption spectra, and Vis-NIR emission spectra were investigated, and the luminescent properties of the polymers were studied in detail. Crystal structures were determined by means of a single-crystal X-ray diffractometer, and all of them proved to have three-dimensional frameworks. Except for polymers 3 and 7, the polymers displayed the characteristic emissions of Ln(III) ions due to the effective sensitization of ligands. At the same time, the 4f orbitals of Ln(III) ions were shifted by the effects of ligand field, which influenced emission spectra and absorption spectra of some of the polymers.