Understanding the effect of 1,10-phenanthroline on the photoluminescent properties of mixed-ligand Lead(II) and Zinc(II) coordination polymers

Two mixed-ligand luminescent coordination polymers (LCPs) [M(3-SBA)(phen)(H 2 O)] n (M = Pb 2+ 1 ; Zn 2+ 2 ; 3-SBA = 3-sulfobenzoate; phen = 1,10-phenanthroline) were synthesized by hydrothermal reaction and characterized using microanalysis, infrared spectra and thermogravitic analysis. Single crystal X-ray diffraction analysis was conducted on both coordination polymers, revealing their one-dimensional (1-D) chain structure. 1 crystallizes in the triclinic space group P ī, where the Pb 2+ ions display a hemidirected coordination geometry. The neighboring Pb 2+ ions are connected into a 1-D chain by 3-SBA ligands via the bidentate-chelating carboxylate group and monodentate sulfonate group. The phen ligands coordinate to the Pb 2+ ions via two N atoms in a conventional chelation mode. 2 crystallizes in the monoclinic space group P2 1 /n . In 2 , the coordination modes of 3-SBA and 1,10-phenanthroline are identical to those in 1 . Intermolecular hydrogen bonds and π⋯π interactions expand the structures of 1 and 2 into a two-dimensional (2-D) and a three-dimensional (3-D) supramolecular network, respectively. Photoluminescence analysis reveals that 1 emits a rare orange phosphorescence in the solid state at room temperature, with the luminescence lifetime of τ 1  = 2.76 ms and τ 2  = 0.23 ms. In contrast, 2 emits a bright blue fluorescence with a total absolute quantum yield of 7.6 %. The theoretical calculation indicates that the auxiliary ligand 1,10-phenanthroline was responsible for both the phosphorescence of 1 and the fluorescence of 2 , while the 3-SBA ligand primarily facilitates bridging the central metal ions to form the frameworks.