Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H(7) (+)O(3) Complex in Solution

Infrared (IR) absorption in the 1000–3700 cm(−1) range and (1)H NMR spectroscopy reveal the existence of an asymmetric protonated water trimer, H(7) (+)O(3,) in acetonitrile. The core H(7) (+)O(3) 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 H(7) (+)O(3) structure in solution. The QM/MM calculations allow for the successful simulation of the measured IR absorption spectra of H(7) (+)O(3) in the OH stretch region, which reaffirms the assignment of the H(7) (+)O(3) 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 H(7) (+)O(3) structure lends itself to promoting irreversible proton transport in presence of even one additional water molecule. We demonstrate how continuously evolving H(7) (+)O(3) structures may support proton transport within larger water solvates.