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 $C_{\rm{2v}}$ structure with double bridging carbonyls is found to compete with the previously proposed triply carbonyl-bridged $D_{\rm{3h}}$ 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.