Microscopic solvation of NaBO2 in water: anion photoelectron spectroscopy and ab initio calculations

Abstract

We investigated the microscopic solvation of NaBO₂ in water by conducting photoelectron spectroscopy and ab initio studies on NaBO₂⁻(H₂O)_n (n = 0–4) clusters. The vertical detachment energy (VDE) of NaBO₂⁻ is estimated to be 1.00 ± 0.08 eV. The photoelectron spectra of NaBO₂⁻(H₂O)₁ and NaBO₂⁻(H₂O)₂ are similar to that of bare NaBO₂⁻, except that their VDEs shift to higher electron binding energies (EBE). For the spectra of NaBO₂⁻(H₂O)₃ and NaBO₂⁻(H₂O)₄, a low EBE feature appears dramatically in addition to the features observed in the spectra of NaBO₂⁻(H₂O)_0–2. Our study shows that the water molecules mainly interact with the BO₂⁻ unit in NaBO₂⁻(H₂O)₁ and NaBO₂⁻(H₂O)₂ clusters to form Na–BO₂⁻(H₂O)_n type structures, while in NaBO₂⁻(H₂O)₃ and NaBO₂⁻(H₂O)₄ clusters, the water molecules can interact strongly with the Na atom, therefore, the Na–BO₂⁻(H₂O)_n and Na(H₂O)_n⋯BO₂⁻ types of structures coexist. That can be seen as an initial step of the transition from a contact ion pair (CIP) structure to a solvent-separated ion pair (SSIP) structure for the dissolution of NaBO₂.