Dual Luminescent Coordination Polymers Based on Flexible Aliphatic Carboxylate Ligands Supplemented by Rigid Bipyridyl Ligands for 2,4-Dinitrophenol (DNP) and Iron(III) Ion Detection

Abstract Based on flexible aliphatic carboxylate ligands supplemented by rigid bipyridyl ligands with isomerized structures, three novel Zn(II) coordination polymers, namely Zn2(dpe)(glutarate)2(H2O)2 (1), Zn2(glutarate)2(tdpe)2(H2O)2 (2) and Zn(H2O)(succinate)(tdpe)2 (3) [dpe = 1,2-di(4-pyridyl)ethylene, tdpe = trans-1-(2-pyridyl)-2-(4-pyridyl)ethylene)], were synthesized by appropriate methods. The crystallographic data of all the complexes present diverse geometries of the Zn(II) centers. There are two independent Zn(II) ions where one is intermediate between square pyramidal and trigonal pyramidal and the other is distorted tetrahedral [in 1] or distorted octahedral [in 2 and 3]. Both carboxylate ligands act as bridging ligands with various coordination modes to build up the main structures, whereas the bipyridyl ligands show only coordination of the 4-pyridyl site with the metal centers, indicating that only dpe acts as a bridging ligand, building up the principal framework in 1. The tdpe ligand presents a monodentate coordination mode in the other two complexes. The structures of all complexes indicate that the coexistence of two ligand types could support higher dimensionalities in the complexes. Complex 1 was further used as a nitroaromatic compound (NAC) and a heavy metal ion sensor. The complex showed highly sensitive and selective sensing of 2,4-dinitrophenol (DNP) and Fe(III) ions, based on its fluorescence quenching effect.