The chemical bonding and adsorption properties of the umbelliform B₆Fe cluster

The interesting report [J. Am. Chem. Soc. 2016, 138, 5644−5651] is that the FeB₆ monolayers have pronounced stabilities, in which planar hypercoordinate Fe atoms are located at the centre of six-membered boron rings. Here, we find that the potential energy surface of the FeB₆ cluster has a single deep funnel that leads down to an umbelliform structure of the global minimum with the triplet state, which is 0.17 eV lower than that of the reported C_2v plane. The chemical bonding analysis by the AdNDP reveals that the FeB₆ has six localised two-centre two-electron (2c–2e) B–B bonds and six localised 2c–2e B–Fe bonds|, and the remaining two 7c–1e σ bonds are delocalised over the umbelliform structure, which is further confirmed by the ELF, LOL and bond order analyses. After the CO molecule is adsorbed on the FeB₆, it prefers to be located at the top site of Fe atom. The adsorption energy is 1.34 eV that is due to the σ-donation from the CO 5σ orbital to the Fe. The charge transfer makes the C–O stretching frequency and bond length have a red-shift.