A potential energy surface survey of OB6: global minima and isomerization stability

In light of the very recent significant discrepancies on the global isomer of the sept-atomic molecule OB₆, we performed a detailed potential energy surface survey of OB₆ covering various isomeric forms. We showed that at the CCSD(T)/6-311+G(2df)//B3LYP/6-311+G(d) level, the planar knife-like isomer 01 with a –BO moiety has the lowest energy, followed by the planar belt-like isomer 02 at 22.6 kcal/mol. Another isomer 05 at 33.1 kcal/mol can be viewed as the direct O-adduct of the pentagonal pyramid B₆. Kinetically, the three isomers 01, 02 and 05 all have considerable barriers (19–29 kcal/mol) (obtained at B3LYP/6-311+G(d) level) against isomerization. However, other isomers either have much higher energy or possess much smaller conversion barriers and are thus of little likeliness for isolation. Moreover, though being isoelectronic to the well-known CB ₆ ^2? molecule, OB₆ does not have any kinetically stabilized wheel-like isomers with O or B centers. The three OB₆ isomers 01, 02 and 05 await future laboratory studies. The detailed results reported in this paper are expected to provide useful information for understanding the growing process of boron oxides, O-doping and oxidation mechanism of boron clusters.