Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H7+ O3 Complex in Solution.

Abstract

Infrared (IR) absorption in the 1000–3700 cm−1 range and 1H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H7 +O3, in acetonitrile. The core H7 +O3 motif persists in larger protonated water clusters in acetonitrile up to at least 8 water molecules. Quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulations reveal irreversible proton transport promoted by propagating the asymmetric H7 +O3 structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H7 +O3 in the OH stretch region, which reaffirms the assignment of the H7 +O3 spectra to a hybrid‐complex structure: a protonated water dimer strongly hydrogen‐bonded to a third water molecule with the proton exchanging between the two possible shared‐proton Zundel‐like centers. The H7 +O3 structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H7 +O3 structures may support proton transport within larger water solvates.