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

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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.
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Funding Information
  • Israel Science Foundation (1587/16. B.P.F)
  • European Research Council

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