Al ₄ H ₇ ⁻ is a resilient building block for aluminum hydrogen cluster materials

The formation and oxygen etching of Al(n)H(m)(-) clusters are characterized in a flow reactor experiment with first-principles theoretical investigations to demonstrate the exceptional stability of Al(4)H(7)(-). The origin of the preponderance of Al(4)H(7)(-) in the mass spectra of hydrogenated aluminum anions and its resistance to O(2) etching are discussed. Al(4)H(7)(-) is shown to have the ability to bond with ionic partners to form stable hydrides through addition of an alkali atom [XAl(4)H(7) (X = Li-Cs)]. An intuitive model that can predict the existence of stable hydrogenated cluster species is proposed. The potential synthetic utility of the superatom assemblies built on these units is addressed.