Be2H3L2− (L=CH3 and F–I): Hyperhalogen anions with ultrashort beryllium-beryllium distances

The superalkali cations and superhalogen anions commonly have different type of core moieties. Based on the previous reports that Be2H3L′2+ (L′=NH3 and noble gases Ne–Xe) are superalkali cations, in the present work, we designed the superhalogen anions Be2H3L2− (L=CH3 and halogens F–I), and both superalkali cations and superhalgen anions can be constructed using Be2H3 as the core moiety. The newly designed Be2H3L2− species are much more stable than their isoelectronic cationic counterparts Be2H3L′2+, as can be reflected by the highly exergonic substitution reaction of L′ ligand in Be2H3L′2+ with isoelectronic L− to give Be2H3L2−. These anionic species possess the well-defined electronic structure, which can be proven by their large HO-MO–LUMO gaps of 4.69 eV to 5.38 eV. It is remarkable that Be2H3L2− can be regarded as the hyperhalogen anions due to the extremely high vertical detachment energies (5.38 eV to 6.06 eV) and the Be–Be distances in these species (1.776 Å to 1.826 Å) are short in ultrashort metal-metal distances (defined as dM–M<1.900 Å) between main group metals. In the designed five small model species, three of them, i.e. Be2H3L2− (L=CH3, Cl, and Br), are kinetical viable global energy minima, which are the promising target for generation and characterization in anion photoelectron spectroscopy. The analogue molecule [t-Bu–Be2H3–t-Bu]− with bulky protecting tert-butyl (t-Bu) groups is designed as a possible target for synthesis and isolation in condensed states.