Insight understanding into influence of binding mode of carboxylate with metal ion on ligand-centered luminescence properties in Pb-based coordination polymers

In the crystal engineering area, it is important to clearly demonstrating the relationship of structure and certain functionality. Herein, we present the study of the relationship of structure with phosphorescent nature for two new room temperature phosphorescence (RTP) coordination polymers (CPs). [Pb(FDA)(H₂O)] (1) and [NH₃(CH₃)NH₂(CH₃)₂][Pb₄(FDA)₅] (2), where H₂FDA is 2,5-furandicarboxylic acid, have been synthesized by solvothermal method using different solvents and Pb²⁺ sources and characterized by microanalysis, powder X-ray diffraction (PXRD), thermogravimetric (TG), IR and UV–vis spectra. The Pb²⁺ ions adopt bicapped triangle prism coordination sphere in 1 and 2, which are connected together via FDA²⁻ ligands into bilayer structure in 1 while pillared-layer framework in 2. The FDA²⁻ ligands show different bridging modes in 1 and 2, leading to distinct coordination interactions between Pb²⁺ ion and FDA²⁻ ligand in both CPs. Both 1 and 2 emit ligand-centered RTP due to the heavy atom of Pb²⁺ ion, with a lifetime and quantum yield of 0.62 ms and 14.9% in 1 versus 1.69 ms and 15.7% in 2. The emission peak shows significant redshift (79 nm) in 2 regarding 1, which arises from their distinction of coordination interactions between Pb²⁺ ion and FDA²⁻ ligand in both CPs.