Hydrogen physisorption on the (BeO)n, B2H4(Be,Ti), and B6Ti3 metal clusters: a computational study of energies and atomic charges.

Abstract

The equilibrium structures of BeO clusters and Be,Ti-decorated boranes were computed with the ωB97X-D method and the 6-31G + (2d,2p) and aug-cc-pVTZ basis sets to study their intermolecular interactions with hydrogen molecules. Thermochemical and molecular properties such as the harmonic vibrational frequency, dipole and quadrupole moments, and atomic charges are employed to understand the attractive interactions that control the adsorption process. Comparison of molecular properties and atomic charges of the studied compounds before and after H2 molecule adsorption shows that most of the interactions among the BeO clusters and boranes with H2 molecules constitute a combination of dispersion, electrostatic, and weak charge transfer interactions. Calculated values of Hirschfeld atomic charges and ΔEe (in parenthesis) (BeO)4.8H2 (0.028 e and -2.0kcal.mol-1), (BeO)2.12H2 (0.030 e and -2.8kcal.mol-1), B6Ti3.10H2 (0.045 e and -15.4kcal.mol-1), and B6Ti3+.10H2 (0.058 e and -15.3kcal.mol-1) show qualitative correlation between hydrogen atomic charges and electronic energy of hydrogen interaction. The ωB97X-D/6-31 + G(2d,2p) values of Gibbs free energy at 298.15K for (BeO)4.8H2 B2H4Ti.4H2 and B6Ti3.10H2 clusters are equal to -5.0, -4.9, and -5.1kcal.mol-1, respectively, which are within the range of energy parameters of materials that could be employed in hydrogen storage tanks for light vehicles.