Chloride salt of oligourea ligand: Synthesis, crystal structure, thermal analyses, and chloride anion binding properties

Abstract

A novel oligourea ligand L, C33H27N11O8, was synthesized by the isocyanate method using 3, 5-diaminopyridine as the initial reactant. The chloride salt 1, TBA2(LCl2)·acetone, was prepared by the liquid-phase diffusion method of ligand L with tetrabutylammonium chloride (TBACl) at room temperature. The ligand L and salt 1 were characterized by 1H NMR, elemental analysis and Fourier transform infrared spectroscopy (FTIR). X-ray single crystal diffraction analysis showed that in the structure of salt 1, two ligands L formed a dimeric species with two appropriate cavities each trapping two chloride anions by multiple N-H···Cl hydrogen bonds. As a structural unit, the dimer was linked to a one-dimensional hydrogen bond chain through the C-H···O hydrogen bond interactions, which was further extended into two-dimensional network structures by C-H···O and C-H···Cl hydrogen bonds. Thermal decomposition properties of the ligand and salt 1 under nitrogen were studied by the TG-DTG method, and the apparent activation energy (Ea) of the main decomposition process was calculated. Furthermore, the selectivity of ligand L to different anions and the binding properties of Cl− anion were investigated by the method of the UV/Vis spectroscopy.