Theoretical design of stable hydride clusters: isoelectronic transformation in the EAlH series

New stable hydrogen-rich metallic hydrides are designed by systematic transformations of the stable known AlH species, carried out by successive isoelectronic substitutions of one aluminum atom by one E-H unit at a time (where E = Be, Mg, Ca, Sr and Ba atoms). Searches on the potential energy surfaces (PESs) of EAlH, EAlH, EAlH and EH systems indicate that structural analogues of AlH become higher energy isomers as the number of E-H units increases. The electronic descriptors: Vertical Electron Affinity (VEA), Vertical Ionization Potential (VIP) and the HOMO-LUMO gap, suggest that the systems composed of EAlH, EAlH, EAlH, with E = Be and Mg, would be the most stable clusters. Additionally, for a practical application, we found that the Be-H and Mg-H substitutions increase the hydrogen weight percentage (wt%) in the clusters, compared with the isoelectronic analogue AlH. The good capacity of beryllium and magnesium to stabilize the extra hydrogen atoms is supported by the increment of the bridge-like E-H-Al, 3center-2electron chemical bonds. Finally, explorations on the PESs of the neutral species (using Na as counterion) indicate that the NaBeAlH, NaBeAlH and NaMgAlH minimum-energy structures retain the original geometric shapes of the anionic systems. This analysis supports the potential use of these species as building blocks for cluster-assembled hydrides in the gas phase.