Solution Structure of Energy Stored System I: Aqua-B(OH)₄^–: A DFT, Car–Parrinello Molecular Dynamics, and Raman Study

Abstract

A systematic study on the structure, stability, and Raman spectra of the metaborate anion hydrated clusters, B­(OH)₄^–(H₂O)_<i>n</i>, (<i>n</i> = 1–15) was carried out by DFT in both gaseous and aqueous phase at the B3LYP/aug-cc-pVDZ level; all of these stable configurations were described, and the most stable hydrated clusters were chosen. The hydrogen bonds in those hydrated clusters were described in three different items: symmetrical double hydrogen bonding (DHB), single hydrogen bonding (SHB), and interwater hydrogen bonding (WHB). The distance of SHB is shorter than that of DHB, and multiple SHBs are more stable than a single DHB. In small size clusters (<i>n</i> ≤ 5), a structure with more DHBs is more stable than other arrangements. With continued increase in size, more SHBs were found in the first hydration sphere: when <i>n</i> ≥ 9, only SHBs can be found, and when <i>n</i> ≥ 12, a full hydration structure is formed with 12 SHBs and a hydration number of 10–12. The Car–Parrinello molecular dynamics simulation shows that only the first hydration sphere can be found, and the hydration number of B­(OH)₄^– is 9.2 and the hydration distance is 3.68. The total symmetrical stretching vibration of B­(OH)₄^– in hydrated B­(OH)₄^–(H₂O)_<i>n</i> is blue shifted with increasing cluster size. After consideration of hydration, the calculated characteristic frequencies are in accord with the experiment characteristic frequency of B­(OH)₄^–