A computational examination on the structure, spin-state energetics and spectroscopic parameters of high-valent FeIVNTs species

Abstract

The imidoiron(IV) species are relatively less explored compared to the oxoiron(IV) intermediates. Recently, generation and characterization of a novel imido/oxoiron(IV) species ([(N₄Py)Fe^IVX]²⁺ X = NTs; 1, O; 2) has been reported with an S = 1 ground state. Although the ground state for 1 and 2 are the same, they are reported to be distinctly different in other aspects. Unlike the oxoiron(IV) species, the Fe(IV) and nitrene combination in 1 lead to eight different spin states. Bearing in mind the complexity arising here, we have undertaken a detailed DFT study on this transient intermediate and probed its electronic structure and bonding in comparison to the oxoiron(IV) unit. Our Molecular Orbital, Energy Decomposition Analysis, and Natural Bond Orbital analysis indicates a weaker σ and non-degenerate π* orbitals for 1 in comparison to a stronger σ and degenerate π* orbitals for 2. The implication of these intricate bonding differences in reactivity is discussed along with the computation of absorption and other spectral parameters. Our results broadly support the proposed S = 1 ground state for 1 and provides some useful insight into its electronic structure.