Microhydration of BH₄^–: Dihydrogen Bonds, Structure, Stability, and Raman Spectra

Abstract

Hydridic-to-protonic interactions in unconventional dihydrogen bonding influence the structure, reactivity, and selectivity in solution and in the solid state. In this study, the structure, stability, and Raman spectra of BH hydrated clusters, [BH(HO)] (n = 1-8, 10, 12, 14, 16) are systematically investigated using density functional theory (DFT) at the wB97XD/6-311++g(3df,3pd) basis set level. The successive microhydration process is described to illustrate in detail the changes in dihydrogen bonding with increasing hydration cluster size. The results of DFT calculations indicate that seven or eight water molecules hydrate BH with a total of 12 dihydrogen bonds in the tetrahedral edge or tetrahedral corner forms, and a maximum of six water molecules in the tetrahedral-edge form. Raman spectra of [BH(HO)] show a blue shift in the B-H stretching band due to hydration. Car-Parrinello molecular dynamics simulations verify strong BH water interactions. The hydration number of BH is 6.7, with a hydration B-O(W) distance of 3.40 Å, and each hydrogen in BH bonds with 2.66 hydrogen atoms from water.

A non-nucleophilic gel polymer magnesium electrolyte compatible with sulfur cathode

“…The structure of MgCl-FTGB was characterized by infrared spectroscopy, Raman spectroscopy and NMR as shown in the Electronic Supplementary Material (ESM). Compared with the infrared spectrum of FTG and Mg(BH4)2, -OH (3,400-3,000 cm −1 ) and B-H bond (2,500-2,000 cm −1 ) [41] are not observed in the infrared spectrum of MgCl-FTGB (Fig. S1 in the Electronic Supplementary Material (ESM)).…”

Understanding the Role of Poly(vinylpyrrolidone) in Stabilizing and Capping Colloidal Silver Nanocrystals

“…Figure S8 shows the SERS spectra of the PVP-capped Ag nanocubes in water before and after the addition of aqueous NaBH 4 solution at a final concentration of 0.05 mg/mL. At t = 10 min, we observed a new peak located at 2396.5 cm –1 , with its assignment to the B–H stretching band of BH 4 – (ν BH ), , while the ν CO(water) band of PVP at 1761.6 cm –1 became extremely weak. This result suggests the adsorption of BH 4 – and desorption of PVP.…”

Dihydrogen Bonds in Aqueous NaBD4 Solution by Neutron and X-ray Diffraction

“…The unusual hydridic-to-protonic interaction, also called dihydrogen bonding, influences the structure, reactivity, and selectivity in solution and the solid state, finding potential utility in catalysis, crystal engineering, and materials chemistry. − NaBH 4 has outstanding gravimetric and volumetric hydrogen densities (ρ m = 10.7 wt %, ρ V = 114.5 kg H 2 /m 3 at room temperature), which makes it one of the most promising chemical hydrides for H 2 storage. − Previous studies show that BH 4 – solvation, especially the dihydrogen bonds, are essential for aqueous NaBH 4 solution for stabilization, hydrogen evolution, hydrogenation, dehydrogenation on catalysts, etc. ,− The solvation structure of BH 4 – is also critical for BH 4 – electrode oxidation. ,− A comprehensive, fundamental understanding of BH 4 – hydration at the molecular level, especially the dihydrogen bonding therein, will also give insight into direct borohydride fuel cell (DBFC) engineering. , …”

“…Quantum mechanics/molecular mechanics (QM/MM) simulation, DFT calculation, and X-ray diffraction studies have shown that water molecules bond with BH 4 – through the tetrahedral-corner or the tetrahedral-edge with much less tetrahedral-face hydration. Taking the interaction numbers of B–D­(W) and D­(B)···D­(W) (Table S5) into consideration, we can conclude that 57%, 53%, and 52% of the hydration water molecules bond to BD 4 – in the tetrahedral-edge form in NaBD 4 ·55D 2 O-298, NaBD 4 ·20D 2 O-298, and NaBD 4 ·10D 2 O-298 solutions, respectively; that is, water tends to hydrate BD 4 – through tetrahedral-edge in the diluted solution.…”

“…We then employed the Multiwfn software to get the reduced density gradient (RDG) and sign­(λ 2 )·ρ function to reveal weak interaction in the BH 4 – hydration clusters. Those configurations were taken from our previous work, , and the electron density is reproduced by B3LYP/6-31G­(d, p) calculation with Gaussian 16B . VMD is used to plot the graphs.…”