Abstract

We performed global minimum searches for the B nH n+2 (n=2-5) series and found that classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series. Relative energies increase from 2.9 kcal mol -1 in B 2H 4 to 62.3 kcal mol -1 in B 5H 7. We believe this occurs because boron atoms in the studied molecules are trying to avoid sp 2 hybridization and trigonal structure at the boron atoms, as in that case one 2p-AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p-AOs and avoiding having one 2p-AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron-hydride clusters as well as for pure boron clusters and boron compounds in general. Classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series B nH n+2 (n=2-5). Relative energies increase from 2.9 kcal mol -1 in B 2H 4 to 62.3 kcal mol -1 in B 5H 7. It is believed that this occurs because boron atoms in the studied molecules tend to avoid sp 2 hybridization and trigonal structures at the boron atoms, as in that case one 2p-AO is empty, and thus highly unfavorable (see figure). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.