Proton transfer in the complex H₃N HCl catalyzed by encapsulation into a C₆₀ Cage

We report proton transfer in the complex H₃N HCi to form the ion pair NH₄⁺Cl^-, which is favored inside the C₆₀ cage according to quantum chemical calculations. The results show that the NH₄⁺Cl^-@C₆₀ is stable with an interaction energy of-2.78 kcal mol^-1. Compared with the complex H₃N HCl without proton transfer, it is found that the C₆₀ cage plays the role of a catalyst for proton transfer. In NH₄ ⁺Cl^-@C₆₀ a negative charge area in the C ₆₀ cage is near the cation NH₄⁺ whereas a positive charge area is near the anion Cl^-. Also, a confinement effect of the C₆₀ cage is noticed, as the endohedral structure of. NH₄⁺Cl^- is more compact than the structure of NH₄⁺Cl^- in the gas-phase complex. These findings indicate that the catalysis by the C₆₀ cage comes from two effects: 1) electrostatic inducement between the C₆₀ cage and endohedral molecules and 2) the confinement effect that compresses endohedral molecular structures inside the C₆₀ cage. In the infrared spectrum, it is found that the confinement effect of the cage can cause large blue shifts of the N-H stretching vibrations in NH₄⁺Cl ^-@C₆₀ compared with those in the NH₄ ⁺Cl^-H₂O complex.