| Abstract
| - Reduction of nitro-aromatic compounds (NACs) proceeds through intermediates with a partial electron transferinto the nitro group from a reducing agent. To estimate the extent of such a transfer and, therefore, theactivity of various model ferrous-containing reductants toward NAC degradation, the unrestricted densityfunctional theory (DFT) in the basis of paired Löwdin−Amos−Hall orbitals has been applied to complexesof nitrobenzene (NB) and model Fe(II) hydroxides including cationic [FeOH]+, then neutral Fe(OH)2, andfinally anionic [Fe(OH)3]-. Electron transfer is considered to be a process of unpairing electrons (without thechange of total spin projection Sz) that reveals itself in a substantial spin contamination of the unrestrictedsolution. The unrestricted orbitals are transformed into localized paired orbitals to determine the orbital channelsfor a particular electron-transfer state and the weights of idealized charge-transfer and covalent electronstructures. This approach allows insight into the electronic structure and bonding of the {Fe(PhNO2)}6 unit(according to Enemark and Feltham notation) to be gained using model nitrobenzene complexes. The electronicstructure of this unit can be expressed in terms of π-type covalent bonding [Fe+2(d6, S = 2) − PhNO2(S =0)] or charge-transfer configuration [Fe+3(d5, S = 5/2) − {PhNO2}- ((π*), S = 1/2)].
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