Ligand Electrochemical Parameter Approach to Molecular Design. σ-Donation, π-Back Donation, and Other Metrics in...

Using the density functional theory, [(N₂)Ru^IIL₅] species are studied in silico. The properties of the Ru-N₂ bond are derived, including σ-donation, π-back donation, Ru-N and N-N bond lengths and bond orders, net charges and NN stretching frequencies, and so forth. These data are correlated using the ligand electrochemical parameter (E_L) theory, whereby the availability of electrons in the [RuL₅] fragment is defined by its electron richness, which is the sum of the E_L parameters, ΣE_L(L₅). The objective is to better understand the binding of the N₂ ligand, leading to a molecular design whereby a specific species is constructed to have a desired property, for example, a particular bond length or charge. We supply cubic expressions linking ΣE_L(L₅) with these many metrics, allowing researchers to predict metric values of their own systems. The extended charge decomposition analysis is used. For the given target, N₂, σ-bonding does not vary greatly with the nature of ligand L, and π-back donation is the dominant property deciding the magnitudes of the various metrics. The E_L parameter provides the path to design the desired species. This contribution is devoted to dinitrogen, but the method is expected to be general for any ligand, including polydentate ligands.