This paper is a theoretical study of beryllium-beryllium bonding, with emphasis on how to strengthen that bond. It deals with the structures and stabilities of several Be2Hn q species (with n = 1, 2 and charge q = -1, 0, +1). The ground states of Be2H, Be2H+, Be2H-, Be2H2, and Be2H2 - are linear, whereas that of Be2H2 + (like Be2H4) is bridged. The Be-Be bond in the linear compounds arises from spσ hybridization on Be, whereas in the bridged isomers it also has pπ contribution (sp2 hybridization). Hydrogenation of the weakly bound Be2 (Re = 4.63 bohr, ωe = 276 cm-1, De ≈ 0.1 eV) strengthens the Be-Be bond significantly, as shown in the hydrides by an average Re(BeBe) of 4.0 bohr for linear and of 3.8 bohr for bridged isomers. The frequencies ωe(BeBe) lie in the range 650 ± 50 cm-1. Hydrogenation to produce Be2H leads to a De(Be-Be) of 1.24 eV, while a second hydrogenation to produce HBe-BeH strengthens it further to 3.20 eV. Both Be2H+ and Be2H- also exhibit a strong De(Be-Be) of ca. 3.30 eV. The process Be2H4 (bridged) → 2BeH2, however, is only 1.38 eV endothermic. The stability of these diberyllium hydrides mainly results from the withdrawal of antibonding charge upon Be2 effected by the attached hydrogen atoms.

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Journal Journal of Physical Chemistry
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Bruna, P.J. (Pablo J.), Di Labio, G.A. (Gino A.), & Wright, J.S. (1992). Beryllium-beryllium bonding. 1. Energetics of protonation and hydrogenation of Be2 and its ions. Journal of Physical Chemistry, 96(15), 6269–6278.