Infrared and NMR Spectroscopic Fingerprints of the Asymmetric H<sub>7</sub><sup>+</sup>O<sub>3</sub> Complex in Solution
Eve Kozari, Mark Sigalov, Dina Pines, Benjamin P. Fingerhut, Ehud Pines
Abstract
Abstract 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.