Unexpected Stability of Al 4 H 6 : A Borane Analog?

Abstract

Whereas boron has many hydrides, aluminum has been thought to exhibit relatively few. A combined anion photoelectron and density functional theory computational study of the Al 4 H – 6 anion and its corresponding neutral, Al 4 H 6 , showed that Al 4 H 6 can be understood in terms of the Wade-Mingos rules for electron counting, suggesting that it may be a borane analog. The data support an Al 4 H 6 structure with a distorted tetrahedral aluminum atom framework, four terminal Al-H bonds, and two sets of counter-positioned Al-H-Al bridging bonds. The large gap between the highest occupied and the lowest unoccupied molecular orbitals found for Al 4 H 6 , together with its exceptionally high heat of combustion, further suggests that Al 4 H 6 may be an important energetic material if it can be prepared in bulk.