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.
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.
authors.affiliation: Department of Theoretical Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland. mj@ich.us.edu.pl
authors.forename: Maria
authors.initials: M
authors.lastname: Jaworska
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Stopa
authors.forename: Zofia
authors.initials: Z
authors.lastname: Stasicka
mesh_terms: D003198:Computer Simulation; D004492:Edetic Acid / Q000737:chemistry*; D004583:Electrons; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D015394:Molecular Structure; D009569:Nitric Oxide / Q000737:chemistry* / Q000302:isolation & purification*; D010084:Oxidation-Reduction; D010777:Photochemistry; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; C055526:Fe(II)-EDTA; D009569:Nitric Oxide; D004492:Edetic Acid; C019179:Fe(III)-EDTA