Encapsulating Proton Inside C60 Fullerene: A Density Functional Theory Study on the Electronic Properties of Cationic X+@C60 (X+ = H+, H3O+ and NH4+).

Abstract

Confining protons into an enclosed carbon cage is expected to give rise to unique electronic properties for both the inner proton and the outer cage. In this work, we systematically investigated the geometric and electronic structures of cationic X+@C60 (X+ = H+, H3O+, and NH4+), and their corresponding neutral species (X = H2O, NH3), by quantum chemical density functional theory calculations. We show that C60 can trap H2O, NH3, H3O+ and NH4+ at the cage center and only slightly influence their geometries. The single proton clings to the inner wall of C60, forming a C-H chemical bond. The encapsulated neutral species almost do not change the electronic structure of the C60, while the internal cations have obvious effects. The charge transfer effect from the inner species to the C60 cage was found for all X@C60 (X = H2O, NH3) (about 0.0 e), X+@C60 (X+ = H3O+, NH4+) (about 0.5 e) and H+@C60 (about 1.0 e) systems. Encapsulating different forms of protons also regulates the fundamental physico-chemical properties of the hollow C60, such as the HOMO-LUMO gaps, infrared spectra, and electrostatic potential, etc., which are discussed in detail. These findings provide a theoretical insight into protons' applications, especially in energy.