Unprecedented 3D-coordination polymeric frameworks of 5-aminoisophthalate with alkaline earth metals (Sr and Ba): catalytic and luminescent properties

Abstract

Herein, two novel 5-aminoisophthalic acid (5-AIP)-based 3D-coordination polymeric complexes (3D-CPs), namely, [Sr₂(5-AIP)₂]_n (1) and [Ba₄(5-AIP)₃(5-AIPH)Cl]_n (2), were synthesized using a facile solvothermal process. They were characterized by UV-visible, FT-IR spectroscopy, single-crystal X-ray diffraction, elemental analysis and thermogravimetric analysis. The XRD analysis of compounds 1 and 2 confirmed the formation of 3D-CPs, crystallized in a triclinic lattice in P space group. Both compounds exhibited similar supramolecular architectures, assembling into a 3D framework from 2D layers through the coordination of the 5-AIP nitrogen atoms with the central metal ions. The presence of a distorted square-planar structural motif with one encapsulated chloride (μ4-chloride) ion at the center of the tetramer (Ba atoms) in 2 made its structure unique. The overall charge was neutralized by the protonation of an –NH₂ group in one of the four 5-AIP ligands present in the monomeric unit. The electronic structure and crystal packing were studied using DFT, non-covalent interaction index (NCI) and Hirshfeld surface analyses. Both complexes were successfully used for catalyzing the bicarbonate-mediated epoxidation of styrene. Tb³⁺ encapsulation in 1 and 2 in methanol at room temperature suggested that 1 outperformed 2 in terms of luminescence and quantum yield.