Intercomponent Interactions in Crown Ether Rotaxanes: The Energetic Influence of Charge

Abstract

Rotaxanes have garnered significant interest due to their functional properties and the dynamics between their components. Nonetheless, the detailed energetic analyses of intercomponent interactions, particularly in crown ether rotaxanes with varying charge states, remain poorly explored in the solid state. There, this study evaluated 13 crystal structures of rotaxanes, comprising six neutral and seven charged, to determine the intercomponent contact areas and stabilization energies. To enable the analyses across systems with different charge states, we propose a methodological approach to evaluate the stabilization energy of charged rotaxanes. This approach integrates rational counterion selection and energetic decomposition into interaction pathways. The results showed that charged rotaxanes exhibited higher stabilization energies (an average of −81.5 kcal mol^–1) compared to their neutral counterparts (an average of −35 kcal mol^–1), attributable to the strengthening of NH···O and CH···O interactions. The total contact area varied across compounds, and the introduction of a second anion slightly increased the contact area without augmenting stabilization energy. Moreover, molecular electrostatic potential surfaces corroborated the influence of charge on intensifying interactions, albeit this increase does not necessarily translate into greater intercomponent stabilization when two charges are involved. In addition to enhancing the understanding of supramolecular interactions in rotaxanes, the results provide a methodological approach applicable to the energetic analysis of charged systems, potentially contributing to future research in supramolecular chemistry.

This study investigated intercomponent interactions in 13 crown-ether-based rotaxanes, comparing neutral and charged systems. An energetic evaluation across different charge states revealed that charged rotaxanes exhibit stronger stabilization primarily due to enhanced NH···O and CH···O interactions. Notably, the increased intercomponent stabilization energy was found to be nonlinear with respect to the number of charges.