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 ns(2) 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. (C) 2018 Elsevier B.V. All rights reserved.