Stereochemically Active and Inactive Lone Pairs in Two Room-Temperature Phosphorescence Coordination Polymers of Pb²⁺ with Different Tricarboxylic Acids

Abstract

Two new Pb²⁺-based coordination polymers (CPs), [Pb₂(HBTC)₂(DMF)] (1) and [Pb(HPTC)] (2), have been synthesized under solvothermal condition; herein, H₃BTC and H₃PTC represent 1,3,5-benzenetricarboxylic acid and 2,4,6-pyridine tricarboxylic acid, respectively. Both 1 and 2 were characterized by microanalysis, infrared spectra (IR), thermal gravimetric analyses (TGA), and powder X-ray diffraction (PXRD) techniques. Single-crystal structural analysis indicates that 1 and 2 show different coordination sphere around Pb²⁺ ions and distinct coordination frameworks. The I¹O² type three-dimensional (3D) nonporous metal-organic framework forms in 1, where the Pb²⁺ ion shows holo-directed coordination geometry, while the I⁰O² type two-dimensional (2D) coordination polymeric layered structure forms in 2, where Pb²⁺ ion shows a hemidirected coordination sphere and the 6s² lone electron pair in Pb²⁺ ion is stereochemically active. The two CPs emit intense and long-lasting greenish phosphorescence in air at room temperature, with absolute quantum yields of 1.2% for 1 and 4.7% for 2 and decay lifetimes of 0.73 ms for 1 and 1.52 ms for 2.