Synthesis, crystal structure and fluorescence property of Cd(Ⅱ) complex containing separate charge centers based on pyridinium zwitterionic ligand

The flexible zwitterion compound 1,1'-((2,3,5,6-tetramethyl-1,4-phenylene)bis(methylene))bis(4-carboxypyridin-1-ium) chloride was used as the ligand to obtain the single crystal of deprotonated ligand (L) by the room temperature volatilization method. Then, a novel coordination compound with separated positive and negative charge centers CdLCl₂(H₂O)₂·H₂O was synthesized with the H₂LCl₂ ligand and CdCl₂ under neutral pH conditions at room temperature. Single-crystal X-ray diffraction results show that the deprotonated ligand L crystallizes in the monoclinic space group I2/m, and its structure has separated charge centers. In addition, the complex crystallizes in the P21/n space group of monoclinic crystal system. The adjacent Cd(Ⅱ) ions are bridged by the concave-shaped ligands L in the same orientation to form a 1D chains. Then these chains are further linked by hydrogen bonds to get three-dimensional supramolecular architecture. The skeleton carries on the characteristics of the ligand. Fluorescence studies show that the complex shows blue fluorescence characteristics similar to that of ligand. However, due to the enhanced conjugation degree and electron transitions, the fluorescence intensity of the complex is stronger than those of ligands, and there is a blue shift of its emission peak, which is at 436 nm.