Synthesis, characterization and thermal decomposition kinetics as well as evaluation of luminescent properties of several 3D lanthanide coordination polymers as selective luminescent probes of metal ions

Abstract

A series of 3D isomorphous and isostructural coordination polymers, namely, {[Ln4(PDA)6(H2O)6]·H2O}∞ (Ln=La, Nd, Sm and Gd; corresponding as-synthesized products are denoted as 1, 2, 3, and 4, respectively; PDA2−=pyridine-2,6-dicarboxylate anion), were synthesized under hydrothermal conditions and characterized by means of elemental analyses, infrared spectrometry, thermal analysis and single crystal X-ray diffraction. In the meantime, the thermal decomposition kinetics of the as-synthesized complexes was investigated under non-isothermal conditions using the Achar differential method and the Coats–Redfern integral method. The room-temperature luminescent properties of the metal-organic frameworks (MOFs) of the lanthanide coordination polymers were measured. It has been found that Ln(III) centers in the complexes adopt eight-coordinated and nine-coordinated modes with N1O7 and N2O7 donors to construct distorted triangular dodecahedral and tricapped trigonal prism configurations, respectively. Based on the building block of tetranuclear homometallic La4C4O8 unit (16-membered ring), lanthanide coordination polymers 1–4 are connected into highly ordered two-dimensional corrugated layers via O—C—O linkers and further assembled into 3D architectures through hydrogen bonds. Besides, lanthanide contraction effect exists in as-synthesized coordination polymers; and the lanthanide coordination polymers possess good selectivity toward metal ions such as Mg2+, Cu2+ and Pb2+, showing promising potential as selective luminescent probes of those metal ions.