The nitrogen position effect on the selectivity of diazacrown ethers to metal ion

In this paper, the nitrogen position isomers of diaza-18-crown-6, diaza-15-crown-5, diaza-12-crown-4, and their complexes with Na+ ion are studied by the density functional theory. Their stable structures are identified by geometry optimization without strict for their geometry. The binding capability that reflects the selectivity of these diazacrown ethers to metallic ions is estimated by the binding energy. The position effects of nitrogen on the stability of these complexes are also investigated by the explicit natural bond orbital and atoms-in-molecule analysis. It is found that different nitrogen position in crown ring will result in different relative energy. To those diazacrown ethers under consideration, the calculation results show that 1,10-diaza-4,7,13,16-tetraoxacyclooctadecane, 1,4-diaza-7,10,13-trioxacyclopentadecane, and 1,7-diaza-4,10-dioxacyclododecane exhibit higher metal binding selectivity than their corresponding nitrogen position isomers, respectively. Clearly, the position of nitrogen plays an important role in the selectivity of diazacrown ethers to metal ions in the system involved. This work will be help for the material design of ionic recognition and other related fields.