Microsolvation of LiBO2 in water: anion photoelectron spectroscopy and ab initio calculations

Abstract

The microsolvation of LiBO₂ in water was investigated by conducting anion photoelectron spectroscopy and ab initio studies on the LiBO₂(H₂O)_n⁻ (n = 0–5) clusters. By comparing calculations with experiments, the structures of these clusters and their corresponding neutrals were assigned, and their structural evolutions were revealed. During the anionic structural evolution with n increasing to 5, hydroxyborate and metaborate channels were identified and the metaborate channel is more favorable. For the hydroxyborate structures, the anionic Li⁺–BO₂⁻ ion pair reacts with a water molecule to produce the LiBO(OH)₂⁻ moiety and three water molecules tend to dissolve this moiety. In the metaborate channel, two types of solvent-separated ion pair (SSIP) geometries were determined as the ring-type and linear-type. The transition from the contact ion pair (CIP) to the ring-type of SSIP starts at n = 3, while that to the linear-type of SSIP occurs at n = 4. In neutral LiBO₂(H₂O)_n clusters, the first water molecule prefers to react with the Li⁺–BO₂⁻ ion pair to generate the LiBO(OH)₂ moiety, analogous to the bulk crystal phase of α-LiBO₂ with two O atoms substituted by two OH groups. The Li–O distance in the LiBO(OH)₂ moiety increases with the increasing number of water molecules and elongates abruptly at n = 4. Our studies provide new insight into the initial dissolution of LiBO₂ salt in water at the molecular level and may be correlated to the bulk state.