ESI-MS Detection of Very Weak π-Stacking Interactions in the Mixed-Ligand Sandwich Complexes Formed by Substituted Benzo-Crown Ethers and Metal Cations

The stability of the mixed-ligand complex formed by amino-benzo-15-crown-5 and nitro-benzo-15-crown-5, with a metal cation, [NH2B15C5 + NO2B15C5 + K]+, was found to be enhanced by π-stacking interactions. This conclusion was deduced by comparison of the abundance of the mixed-ligand complex with the abundances of homo-ligand complexes ([(NH2B15C5)2 + K]+, [(NO2B15C5)2 + K]+), as well as with those of 1:1 complexes ([NH2B15C5 + K]+, [NO2B15C5 + K]+). Some solvents and some metal cations with large radii were also found to prevent the existence of π-stacking interactions.

Graphical AbstractThe stability of mixed-ligand complex formed by amino-benzo-15-crown-5 and nitro-benzo-15-crown-5, ion [NH2B15C5 + NO2B15C5 + K]+, was found to be enhanced by π-stacking interactions.Figure optionsDownload full-size imageDownload high-quality image (64 K)Download as PowerPoint slide