Trapping of H2− in aluminum hydride, Al4H14−

Abstract

Ever since our first experimental and computational identification of Al4H6 as a boron analog [X. Li et al., Science 315, 356 (2007)], studies on aluminum hydrides unveiled a richer pattern of structural motifs. These include aluminum-rich hydrides, which follow shell closing electron counting models; stoichiometric clusters (called baby crystals), which structurally correspond to the bulk alane; and more. In this regard, a mass spectral identification of unusually high intense peak of Al4H14−, which has two hydrogen atoms beyond stoichiometry, has remained mostly unresolved [X. Li et al., J. Chem. Phys. 132, 241103 (2010)]. In this Communication, with the help of global minima methods and density functional theory-based calculations, we identify the lowest energy bound structure with a unique Al–H–H–Al bonding. Our electronic structural analysis reveals that two Al2H6 units trap a transient, metastable H2−. In other words, three stable molecules, two Al2H6 and an H2, are held together by a single electron. Our studies provide a pathway to stabilize transient species by making them part of a more extensive system.

Hydrogen Storage Capacity of Single-Nb-Atom-Doped Al Clusters in the Gas Phase Revealed by Thermal Desorption Spectrometry

“… Indeed, Bowers and co-workers found that the activation barriers of chemisorption of H 2 on Al n + with n = 10–27 are quite high, such that the rate constants at RT are effectively zero . By contrast, Bowen and co-workers reported that H-rich Al n H p + clusters were generated using pulse arc cluster ion source (PACIS), in which H atoms were richly prepared in a plasma during cluster formation. ,,, Hence, we can infer that dissociation of H 2 is the bottleneck in the process, although Al clusters themselves have a high affinity to H atoms.…”

“…26 By contrast, Bowen and coworkers reported that H-rich Al n H p + clusters were generated using pulse arc cluster ion source (PACIS), in which H atoms were richly prepared in a plasma during cluster formation. 5,6,27,28 Hence, we can infer that dissociation of H 2 is the bottleneck in the process, although Al clusters themselves have a high affinity to H atoms.…”

“…Previous studies revealed that aluminum clusters are not reactive against H 2 . However, other studies also suggested the importance of aluminum hydride clusters to develop hydrogen storage materials. − Generation of aluminum hydrides also requires a high temperature and high pressure. In order to lower the high activation barrier in the reaction between hydrogen gas and aluminum clusters, transition metal atoms, such as Rh, Co, Nb and V, were introduced and hydrogenation of transition metal and transition metal-doped aluminum clusters was investigated, revealing the importance of charge transfer and geometric effect in the process. − A recent study reported that doping of a single niobium atom on an aluminum cluster in the gas phase drastically promotes the hydrogenation of the clusters .…”