Syntheses, Crystal Structures and Luminescent Properties of a Series of Ag-Ln Coordination Polymers

Nine novel Ag-Ln coordination polymers, {[LnAg(2,6-PDA)(2)(H2O)(3)]mH(2)O}(n) (Ln=Pr 1, Nd 2, m=2; Ln=Sm 3, Gd 4, Dy 5, Tb 6, m=3; Ln=Eu 7, Ho 8, Er 9, m=1; 2,6-PDA=pyridine-2,6-dicarboxylic acid), were synthesized under hydrothermal methods. They were characterized by single-crystal X-ray diffraction, elemental analysis, IR, UV-Vis-NIR (Ultraviolet-Visible-Near Infrared) absorption and fluorescent emission spetra. In crystals, pyridine-2,6-dicarboxylates adopt four coordination modes to bridge Ag(I) and Ln(III) ions, i.e., polymers 1 and 2 present 2D layers and polymers 3-9 possess 1D chain structure. The emphasis is on the research of luminescent properties. All of the polymers show characteristic emissions owing to the effective sensitization from the Ag-ligand section with the introduction of Ag(I) ion. Due to the influence of crystal field and 4d orbitals of Ag(I), the NIR emission bands of Ln(III) polymers present shift, broad and split, and some absorption bands of f-f* transitions also show shift, broad and split in their UV-Vis-NIR spectra, so the two spectra can evidence each other.