Syntheses, crystal structures and photophysical properties of a series of Zn-Ln coordination polymers

A series of coordination polymers, {[LnZn(2,3-pydc)(1,3-bdc)(OH)(H2O)m]·H2O}n, (Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5, Er 6, Yb 7, Pr 8, Nd 9), (1–7, m = 1; 8, 9, m = 2), (2,3-H2pydc = pyridine-2,3-dicarboxylic acid, 1,3-H2bdc = isophthalic acid), are synthesized by the hydrothermal method and their crystal structures are determined by single-crystal X-ray diffraction. Structural analysis shows that coordination polymers 1–9 present two-dimensional layered structures and all of them are crystalized in triclinic system with space group Pī. Hereinto polymers 1–7 are isomorphous, while polymers 8 and 9 are also isomorphous and each of them includes one more coordinated water molecule than others. All coordination polymers are characterized by IR, UV–Vis–NIR and fluorescent spectra, and the luminescent properties are the research emphasis. In addition, except for polymer 3, the other eight Zn-Ln polymers exhibit the characteristic luminescence of corresponding Ln(III) ions, which should be owing to the sensitization of the Zn-Ligand moiety. With the influence of the crystal field and the introduction of Zn(II) ion, the internal energy levels of the system are tuned, which is reflected by shift and split of the partial characteristic bands of Ln(III) ions in their UV–Vis–NIR absorption spectra and NIR emission spectra, and both can corroborate each other.