Triply Carbonyl-Bridged Ni₂(CO)₅Featuring Triple Three-Center Two-Electron Ni—C–Ni Bonds Instead of Ni≡Ni Triple Bond

Motivated by the predicted unusual short Ni—Ni bond length that is comparable to the intermetallic distance anticipated for the triple bond, the nature of Ni—Ni bonding interaction in the triply carbonyl-bridged geometry of the neutral Ni2(CO)5 complex has been investigated using a range of state-of-the-art quantum chemistry methods. The elaborate analyses manifest that the tribridged Ni2(CO)5 features triple three-center two-electron Ni—C—Ni bonds instead of Ni≡Ni triple bond. The electron pair donated by the bridging carbonyl ligand should be shared by both nickel centers to achieve the favored (18, 18) configuration.