Competition between (18, 18) and (18, 16) Configurations in Ni₂(CO)₅: An Isomerization Energy Decomposition Analysis

The potential energy landscape of the neutral Ni_2(CO)_5 complex was re-examined. A new C_\rm2v structure with double bridging carbonyls is found to compete with the previously proposed triply carbonyl-bridged D_\rm3h isomer for the global minimum of Ni_2(CO)_5. Despite that the tri-bridged isomer possesses the more favored (18, 18) configuration, where both metal centers satisfy the 18-electron rule, the neutral Ni_2(CO)_5 complex prefers the di-bridged geometry with (18, 16) configuration. The isomerization energy decomposition analysis reveals that the structural preference is a consequence of the maximization of electrostatic and orbital interactions.