Photophysical properties and DFT calculations of a phosphorescent lead(II) coordination polymer with 2-chloronicotinate

A new phosphorescent coordination polymer [Pb(2-ClNA) 2 ] n ( 1 ) (2-ClNA = 2-chloronicotinate) was synthesized by the solvent method and characterized using microanalysis, IR spectrum, and thermogravimetric analysis. Single crystal structure analysis reveals that 1 crystallizes in the orthorhombic space group P 2 1 2 1 2 1 . In the structure of 1 , the Pb 2+ ion is seven-coordinated with a holodirected coordination geometry. Two kinds of inequivalent 2-chloronicotinate ligands link Pb 2+ ions to form a three-dimensional (3-D) network framework in μ 3 -κ 2 O1, O2: κ 1 O1: κ 1 O2 and μ 3 -κ 1 O3: κ 1 O4: κ 1 N2 modes, respectively. The 2-chloronicotinate ligands are evenly distributed around the Pb 2+ ions, and π⋯π stacking occurs only in two directions. At ambient conditions, 1 emits bright cyan phosphorescence with a lifetime of 2.76 ms and an absolute quantum yield as high as 16.25% under ultraviolet irradiation. Photophysical analysis reveals that the luminescence of 1 arises from the n → π* transition of the 2-chloronicotinate ligand. The density functional theory (DFT) calculations clarify the luminescence process, confirming that the phosphorescence of 1 is attributed to ligand-centered emission and that the 6s states of the Pb 2+ ions play a significant role in it.