From Statistical Mixtures to Structural Insights: Characterisation of Heterometallic [M4L6]8+ Coordination Cages using High Resolution Ion Mobility Mass Spectrometry

Abstract

The three-dimensional, non-symmetrical cavities of many biological systems such as enzymes and transport proteins have been shown to routinely distinguish between substrates with minute structural differences, even down to a single atom, often enabling highly selective catalysis and molecular recognition. Inspired by the level of precision from these systems, low-symmetry coordination cages are emerging as highly-desirable synthetic targets. Their inherent complexity, however, presents a significant challenge to chemical characterisation and is thus a barrier for convergent preparation.Using high-resolution ion mobility-mass spectrometry (IM-MS), we demonstrate the successful resolution and characterisation of heterobimetallic [M₄L₆]⁸⁺ metallosupramolecular coordination cages, which differ only in their metal ion composition. Using this facile compositional analysis, we show that cage composition can be controlled by the stoichiometry of the reagent metal salts. Furthermore, IM-MS enables the identification and interrogation of individual mixed metal assemblies from a complex mixture of cages which cannot be performed in solution, enabling the relative stability of each congener to be determined. IM-MS guided synthesis represents a paradigm shift in the accelerated development of supramolecular sensors and catalysts that embraces the complexity of a systems approach rather than focusing on exclusively pure materials.