A theoretical survey on the structures, energetics, and isomerization pathways of the B 5 O radical

Boron‐centered radicals have received growing interest. Recently, two groups reported density functional theory investigations (GGA‐PW91 and B3LYP) on a hexa‐atomic boron‐oxide radical, B 5 O, which has led to great discrepancies on the type of low‐lying structures. In this article, we not only explore the energetics of doublet and quartet B 5 O isomers at high electron‐correlated levels (CCSD(T)/6‐311+G(2df), CCSD(T)/aug‐cc‐pVTZ, and G3B3) but also investigate the isomerization and fragmentation stability of the low‐lying B 5 O isomers. All the high‐level studies consistently show that the B 5 O radical possesses a belt‐like ground structure 2 01 in doublet electronic state followed by isomer 2 02 with an exocyclic BO moiety at around 3.0 kcal/mol. Kinetically, 2 01 and 2 02 are separated by a considerable barrier of about 20 kcal/mol. Thus, the two isomeric forms of B 5 O radical should be very promising for isolation in laboratory. However, the other four isomers reported recently are all kinetically unstable toward conversion to 2 01 and 2 02 . The high thermodynamic and kinetic stability of 2 01 and 2 02 might make them as important building cores in the growth of boron‐oxide clusters. This results would also help deeply understand the oxidation and doping mechanism of pure boron clusters. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011