Quantitative Descriptions of Dewar-Chatt-Duncanson Bonding Model: A Case Study of Zeise and Its Family Ions.

Historically, Dewar-Chatt-Duncanson (DCD) model is a heuristic device to advance the development of organometallic chemistry and deepen our understanding of the metal-ligand bonding nature. Zeise's ion, the first man-made organometallic compound and a quintessential transition metal-olefin complex, was qualitatively explained using the DCD bonding scheme in 1950s. In this work, we quantified the explicit contributions of the σ donation and π back-donation to the metal-ligand bonding in Zeise and its family ions, [PtX 3 L] - (X=F, Cl, Br, I, and At; L=C 2 H 4 , CO, and N 2 ), using state-of-the-art quantum chemical calculations and energy decomposition analysis. The relative importance of the σ donation and π back-donation depends on both X and L, with [PtCl 3 (C 2 H 4 )] - being a critical case in which the σ donation is marginally weaker than the π back-donation. The changes along this series are controlled by the energy levels of the correlated molecular orbitals of PtX 3 - and ligand L. This study deepens our understanding of the bonding properties for transition metal complexes beyond the qualitative description of the DCD model.