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Fostering the Basic Instinct of Boron in Boron–Beryllium Interactions

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journal contribution
posted on 14.03.2018 by M. Merced Montero-Campillo, Ibon Alkorta, José Elguero
A set of complexes L2HB···BeX2 (L = CNH, CO, CS, N2, NH3, NCCH3, PH3, PF3, PMe3, OH2; X = H, F) containing a boron–beryllium bond is described at the M06-2X/6-311+G­(3df,2pd)//M062-2X/6-31+G­(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to −283.3 kJ/mol ((H2O)2HB···BeF2). The stabilization of these complexes is possible thanks to the σ-donor role of the L ligands in the L2HB···BeX2 structures and the powerful acceptor nature of beryllium. According to the topology of the density, these B–Be interactions present positive laplacian values and negative energy densities, covering different degrees of electron sharing. ELF calculations allowed measuring the population in the interboundary B–Be region, which varies between 0.20 and 2.05 electrons upon switching from the weakest ((CS)2HB···BeH2) to the strongest complex ((H2O)2HB···BeF2). These B–Be interactions can be considered as beryllium bonds in most cases.