Attaching Be or Mg to BH3 results in the formation of BeBH3 and MgBH3 molecules capable of forming stable anions

Highlights: • BeBH₃ and MgBH₃ are stable molecules not susceptible to any fragmentation. • Be or Mg ns² lone pair donation to empty 2p boron orbital results in strong bonding. • (BeBH₃)⁻ anion is adiabatically (EA = 1.114 eV) and vertically (VDE = 1.301 eV) stable. • (MgBH₃)⁻ anion is adiabatically (EA = 0.675 eV) and vertically (VDE = 0.744 eV) stable. Stability of BeBH₃ and MgBH₃ molecules and their (BeBH₃)⁻ and (MgBH₃)⁻ anions is investigated on the basis of correlated ab initio calculations. The electronic and thermodynamic stability of all species is confirmed by estimating the excess electron binding energies of the anions and by evaluating the Gibbs free energies for various fragmentation paths. The bonding effects in BeBH₃ and MgBH₃ have been identified as the result of alkaline earth metal ns² lone-pair donation to the empty 2p boron orbital. Adiabatic and vertical electronic stabilities of the (BeBH₃)⁻ and (MgBH₃)⁻ anions were found to span 1.114–1.301 and 0.675–0.744 eV range, respectively.