Theoretical Study of the Structure and Stability of Layerwise Hydrogenated Aluminum Clusters Al44Hn and Al89Hm

Resumo

Structural parameters, energies, and spectroscopic characteristics of two series of layerwise hydrogenated aluminum clusters Al₄₄H_n (n = 27–44) and Al₈₉H_m (m = 15, 24, 39, and 63) have been calculated by the density functional theory method. It has been shown that increasing number of H atoms in both series entails rapid enhancement of structural distortions up to cooperative rearrangements accompanied by a change in the shape and composition of the surface layer and internal core of the cluster. At the end of the first series Al₄₄H_n, several surface atoms migrate to the outer sphere of the cage to form valence-unsaturated “outer-surface” AlH_n and Al₂H_n moieties, which can be active sites at the stages of deeper hydrogenation. Simultaneously, the inner core [Al]₅ disintegrates, and its atoms are introduced into the surface layer. A family of “inverted” Al₄₂H₄₂ isomers with the hollow [Al₄₂] cage has been localized; the isomers contain the endohedral AlH₄ group and “inner” Al-H bonds with their hydrogen end directed to the center of the inner cavity. At the end of the second series, five alanate groups AlH₄ and two Al₃H₂ fragments bonded to the surface through hydrogen bridges are formed in the outer sphere of the \(\rm{Al}_{89}H_{63}^-\) cluster. The results are of interest for DFT modeling of hydrogenation of nanosized aluminum clusters at the molecular level.