Infrared and NMR spectroscopic fingerprints of the asymmetric H7+O3 complex in solution.

Infrared (IR) absorption in the 1000-3700 cm -1 range and 1 H NMR spectroscopy reveals 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. QM/MM MD simulations reveal irreversible proton transport promoted by propagating the asymmetric H 7 + O 3 structure in solution. Successful simulation of the IR absorption of H 7 + O 3 in the OH stretch region reaffirms the H 7 + O 3 hybrid structure of our QM/MM calculations: a protonated water-dimer strongly hydrogen-bonded to a third water molecule. 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.