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  • Title: Photochemical NO-removal and NOx-release in the presence of Fe-EDTA complexes. DFT calculations of electronic structure and spectroscopy of the [Fe(edta)(NO)]2- complex.
    Author: Jaworska M, Stopa G, Stasicka Z.
    Journal: Nitric Oxide; 2010 Nov 01; 23(3):227-33. PubMed ID: 20633692.
    Abstract:
    The calculations for iron complexes with EDTA and NO, [Fe(II)(edta)(NO)](2-) and [Fe(III)(edta)(NO)](-), were performed with the DFT/B3LYP method. The lowest energy structure for the Fe(II) complex is six-coordinated with one carboxylate group unbound. The Fe-NO bond is here short and strengthen additionally by the charge shift to form Fe(III)NO. The low stability of the [Fe(III)(edta)(NO)](-) complex can be interpreted in terms of the weak Fe-NO bond calculated for this species. Photoreduction of the [Fe(III)(edta)(H(2)O)](-) or [Fe(III)(edta)(OH)](2-) complex by EDTA in the NO atmosphere was studied and is suggested as convenient method of the [Fe(edta)(NO)](2-) synthesis. The results of the [Fe(edta)(NO)](2-) irradiation connotes also a possibility of alternative release NO or N(2)O in acidic or alkaline solution, respectively. The calculated electronic spectrum of [Fe(edta)(NO)](2-) showed that low and medium energy bands are mainly of pi(NO)(*)/d-->d/pi(NO)(*), while transitions from free electron pairs of nitrogen and oxygen atoms to metal d and nitrosyl pi(NO)(*) orbitals are responsible for the high energy band. The former favors homolytic dissociation of the neutral NO molecule, whereas the latter heterolytic Fe-NO bond cleavage. In both cases excitation leads to weakening of the Fe-NO bond, enabling the pH effect on dissociation of neutral NO molecule or NO anion. This outcome allows to control the NO(x) delivery by two stimuli: light and solution pH.
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