Study on the structure and two-dimensional correlation spectra of Cd(II) complexes based on flexible carboxylic ligands

Abstract

A three-dimensional supramolecular reticular Cd(II) complex [Cd (PCPA) 2 (4,4′-bipy)]n was synthesized by hydrothermal method using PCPA and 4,4′-bipy as ligands. The structure of compound 1 was characterized by single crystal X-ray diffraction, elemental analysis, infrared spectroscopy, two-dimensional infrared correlation spectroscopy under thermal perturbation, thermogravimetric analysis and fluorescence spectroscopy. The results of single crystal X-ray diffraction analysis show that compound 1 belongs to monoclinic system and C2/c space group. Compound 1 forms a two-dimensional lamellar structure by bridging PCPA and 4,4 ′-bipy, and a three-dimensional supramolecular structure by π … π and C–H … π action. Two-dimensional infrared data of thermal perturbation show that the response peaks of flexible group νas (–CH2–) and unsaturated ν (Ar–H) to thermal perturbation are at 2936 cm−1, 3081 cm−1 and 3068 cm−1, but the response peaks of νas (–CH2–) are stronger than that ofν (=C–H) and more sensitive to temperature changes. The strong peak near 1590 cm−1 isν(benzene ring breathing) response to thermal perturbation, and the peak intensity is the largest. It is worth noting that the aromatic rings in compound 1 have C–H … π and π … π stacking, and these weak effects are sensitive to temperature changes, thus conducting the response to temperature changes to the aromatic rings, making the aromatic rings also sensitive to thermal perturbation. At the same time, the fluorescence properties of compound 1 were tested. Under 296 nm light excitation, the ligand PCPA has a strong emission peak at 313 nm and a weak acromion at 371 nm, which may be caused by the π*→π and weak π*→n transitions in the ligand, respectively. Under 369 nm light excitation, ligand 4,4′-bipy has a strong emission peak at 496 nm and a strong acromion at 459 nm.