OsB : An Aromatic Osmium-Centered Monocyclic Boron Ring.

Transition-metal-centered monocyclic boron wheels are important candidates in the family of planar hypercoordinate species that show intriguing structure, stability and bonding situation. Through the detailed potential energy surface explorations of MB (M = Fe, Ru, Os) clusters, we introduce herein OsB to be a new member in the transition-metal-centered borometallic molecular wheel gallery. Previously, FeB and RuB clusters were detected by photoelectron spectroscopy and the structures were reported to have singlet symmetry. Our present results show that the global minimum for FeB has a molecular wheel-like structure in triplet spin state with symmetry, whereas its heavier homologues are singlet molecular wheels with symmetry. Chemical bonding analyses show that RuB and OsB display a similar type of electronic structure, where the dual σ + π aromaticity, originated from three delocalized σ bonds and three delocalized π bonds, accounts for highly stable borometallic molecular wheels.