A Dynamic Proton Bond: MH⁺·H₂O ⇌ M·H₃O⁺ Interconversion in Loosely Coordinated Environments

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Computational Chemistry

Background:

• Organic molecules interacting with oxonium cations can form dynamic supramolecular structures.
• Proton-bound complexes of water with polyether macrocycles serve as a model system for studying these interactions.
• Understanding host-guest chemistry in solvation shells is crucial for various chemical processes.

Purpose of the Study:

• To investigate the dynamic behavior of proton-bound complexes formed between water and polyether macrocycles.
• To characterize the host-guest chemical identity changes in these supramolecular systems.
• To explore the vibrational signatures associated with proton delocalization and transfer.

Main Methods:

• Infrared action ion spectroscopy was employed over a broad spectral range.
• Ab initio molecular dynamics simulations were performed to model the observed phenomena.
• Analysis of vibrational spectra to identify characteristic bands and diffuse features.

Main Results:

• Water retains the proton, forming hydronium ions (H3O+) within the polyether macrocycle solvation shell.
• Increasing coordination number enhances the stability of the (ether)·H3O+ complex.
• Dynamic, reversible interconversion between (ether)·H3O+ and (etherH+)·H2O configurations was observed.
• Experimental vibrational spectra showed characteristic bands for limiting configurations and diffuse bands for proton delocalization.

Conclusions:

• The study reveals dynamic supramolecular structures with changing host-guest chemical identity in proton-bound water-polyether systems.
• Proton delocalization and reversible proton transfer are key features, not adequately described by static models.
• Ab initio molecular dynamics accurately models the complex vibrational signatures arising from dynamic proton bonding.