Observation of the Single‐ and Double‐Well Hydrogen Bonding in <scp> HSO ₄ </scp> ⁻ • <scp>HX</scp> and <scp> H ₂ SO ₄ </scp> • X ⁻ (X = F, Cl, Br, I, At)

ABSTRACT In this study, the theoretical and computational investigation on the geometry, electronic structure, chemical bonding, IR spectra and thermodynamic properties of two competitive isomers of HSO 4 − • HX and H 2 SO 4 • X − (X = F, Cl, Br, I, At) with single‐ or double‐well hydrogen‐bond potential were performed by using the DFT and CCSD(T) calculations. The asymmetric double‐well hydrogen‐bond potential exists in the HSO 4 − • HF and symmetric single‐well hydrogen‐bond potential exists in the H 2 SO 4 • X − (X = Cl, Br, I, At), respectively. It can also be predicted that the HSO 4 − • H + • Ts − prefers the H 2 SO 4 • Ts − structure by forming the double‐well hydrogen bonding rather than the HSO 4 − • HTs structure with single‐well hydrogen bonding. Furthermore, the AdNDP, QTAIM, IRI, RDG/NCI, PIO and EDA analyses were also performed in order to explore the interaction of hydrogen bonding. Considering the penetration effect and shielding effect of electrons, the overlaps between the np orbitals of X − (X = F, Cl, Br, I, At) and 1 s orbital of hydrogen atom influence the strength and stability of the hydrogen bonds due to the non‐negligible covalent interaction. The strong electronegativity, small ionization radii, and overlap between the 2p orbitals of F − ion and 1 s of H atom result in the dominant formation of HSO 4 − • HF complex. The observation and explanation of the single‐ and double‐well hydrogen‐bond potential in HSO 4 − • H + • X − provide new insights into proton chemistry, behaviors of strong acids, halogen effects, and fundamental theory of hydrogen bonds.