Comparative Studies on Optical and Electronic Behavior of Lanthanide-based Coordination Polymers: Synthesis, Structure, Absorption-Emission and Magnetic Properties

Abstract

A series of lanthanide(III) based coordination polymers have been synthesized using chelidamic acid (CA) as a ligand, $$[\hbox {Ln}(\hbox {C}_{7}\hbox {H}_{2}\hbox {NO}_{5})(\hbox {H}_{2}\hbox {O})_{3}].\hbox {H}_{2}\hbox {O}$$ (Ln = Eu, Gd, Tb, and Dy). All the compounds were prepared by solvothermal technique using $$\hbox {H}_{2}\hbox {O-DMF}$$ as solvents (4:1, volume ratio). Compounds were characterized through various instrumental techniques such as single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis, IR spectroscopy, etc. In all the cases lanthanide ion adopts distorted dodecahedron geometry. And these dodecahedrons are connected through chelidamic acid ligand to form the two-dimensional structure. These layers are H-bonded to form the three-dimensional supramolecular structure. The optical band gap energy measurements exhibit that the variation of the band gap energy is independent of the f-electrons. This is due to the weak bonding connectivity between the metal ion and ligands, which could not perturb the density of states significantly. The variable-temperature magnetic measurements exhibit the paramagnetic behavior of all the compounds though the effective magnetic moments rise with increasing number of f-electrons. The present study illustrates the usefulness of the lanthanides for the structure building as well as the role of f-electrons for opto-electronic behaviors. SYNOPSIS A series of two-dimensional isostructural Lanthanum coordination polymers have been synthesized and comparisons of various properties have been made. Figure shows the reaction scheme for the observed coordination polymer.