Molecular recognition by multiple metal coordination inside wavy-stacked macrocycles.

Abstract

Most biological and synthetic receptors for small organic molecules employ a combination of relatively weak intermolecular interactions such as hydrogen bonds. A host compound that utilizes stronger yet reversible bonding in a synergistic manner could realize precise recognition, but the regulation and spatial arrangement of such reactive interaction moieties have been a challenge. Here, we show a multinuclear zinc complex synthesized from a macrocyclic ligand hexapap, which inwardly arranges labile metal coordination sites for external molecules. The metallomacrocycle forms a unique wavy-stacked structure upon binding a suitable length of dicarboxylic acids via multipoint coordination bonding. The saddle-shaped deformation and dimerization realize the differentiation of the interaction moieties, and change of guest-binding modes at specific metal coordination sites among the many present have been achieved utilizing acid/base as external stimuli.Synergistic use of coordination bonds that are strong and reversible realizes unique molecular recognition in artificial systems. Here, the authors show that a zinc-based metallomacrocyle can bind dicarboxylic acids of suitable length at specific metal sites by shape deformation and dimerization.