Theoretical Study of the Structure and Stability of Layerwise Hydrogenated Aluminum Clusters Al 44 H n and Al 89 H m

Structural parameters, energies, and spectroscopic characteristics of two series of layerwise hydrogenated aluminum clusters Al 44 H n ( n = 27–44) and Al 89 H 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 Al 44 H n , several surface atoms migrate to the outer sphere of the cage to form valence-unsaturated “outer-surface” AlH n and Al 2 H 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” Al 42 H 42 isomers with the hollow [Al 42 ] cage has been localized; the isomers contain the endohedral AlH 4 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 AlH 4 and two Al 3 H 2 fragments bonded to the surface through hydrogen bridges are formed in the outer sphere of the Al_89H_63^- cluster. The results are of interest for DFT modeling of hydrogenation of nanosized aluminum clusters at the molecular level.