Spin-state bifurcation between hydrogenation and oxygen activation in [Fe(Cp)(CO)₂]: a DFT study toward a spin-aware molecular d-manifold descriptor.

Authors

Frans Augusthinus Asmuruf, Supeno Supeno, Ilham Salim, Yohanis Irenius Mandik, Jonathan Kiwasi Wororomi

Published in

Journal of molecular modeling. Volume 32. Issue 9. Aug 10, 2026. Epub Aug 10, 2026.

Abstract

Spin-state effects can reshape the thermodynamic accessibility of molecular iron intermediates, but their incorporation into descriptor-based catalyst models remains challenging because molecular complexes exhibit discrete, spin-dependent orbital manifolds rather than continuous d-bands. Here, [Fe(Cp)(CO)₂] is examined by DFT as a spin-state-dependent thermodynamic network connecting H₂-derived and O₂-derived basins. The calculations show that CO dissociation exposes a strongly quartet-compatible FeCp(CO) fragment, whereas the σ-H₂ basin is consistently doublet-favored. O₂-derived η¹-O₂ and η²-peroxo structures are best described, more conservatively, as spin-flexible open-shell basins, because their ordering is functional-dependent and several formally doublet solutions exhibit substantial spin contamination. The descriptor is therefore not presented as a kinetic predictor, but as a computed spin-resolved Fe-3d orbital metric that rationalizes the electronic distinction between the hydrogenation and oxygen-activation basins.
Geometry optimizations and harmonic frequency calculations were performed primarily at the unrestricted ωB97X-D/def2-TZVP level using Q-Chem. Gibbs energies were reconstructed from the Q-Chem thermochemical output and used only for stoichiometry-normalized thermodynamic pathway mapping. Functional sensitivity was evaluated by PBE0-D3(BJ), TPSSh-D3(BJ), and B3LYP-D3(BJ) single-point calculations for FeCp(CO), σ-H₂, η¹-O₂, and η²-peroxo spin gaps. Additional NBO-based population analyses and molecular-orbital coefficient analyses were used to extract Fe natural charges, Fe spin populations, Fe 3d occupancies, and spin-resolved Fe-3d molecular-orbital centroids. No transition-state or IRC calculations are reported; consequently, all mechanistic language is limited to thermodynamic basin mapping.

PMID:
42573877
Bibliographic data and abstract were imported from PubMed on 10 Aug 2026.

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