Fostering the Basic Instinct of Boron in Boron-Beryllium Interactions.

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.