QTAIM study of the interactions in di-chalcogenide-bridged homometallic tri-iron carbonyl clusters: [M′2Fe3(CO)10]−2 (M′ = S, Se, Te)

Using the Quantum Theory of Atoms in Molecules (QTAIM), we explored the bonding characteristics of di-chalcogenide-bridged tri-iron carbonyl clusters [M′₂Fe₃(CO)₁₀]⁻². The properties of the bond critical points, identified in our investigation, align with the previously reported results for transition metal clusters of comparable structure. They include the electron density (ρ_b), the electron density Laplacian (∇²ρ_b), the local energy density H_b, the local kinetic energy density G_b(r), the local potential energy density V_b, the ellipticity ε_b, and the bond delocalization indices δ(A, B). A study of the tri-iron metal core centers reveals no direct paths of the bond or bond critical sites between these metals. Despite the fact that no direct bond paths are observed between the iron atoms bridged by di-chalcogenide ligands, there are indications of enhanced organometallic bonding between the iron atoms. The values of the nonbonding delocalization indices indicate a five center, seven electron (5c–7e) bonding interaction associated with a five-membered Fe₃(μ-M′)₂ ring. The bonding interactions with covalent and electrostatic character are identified in the Fe–M′ bonds (where M′ = S, Se, or Te). The pi-back donation from CO ligands to Fe is also found in strong levels for all compounds, as revealed through the Fe–CO bond delocalization indices δ(Fe···O).