title: Spin density distribution in five- and six-coordinate iron(II)-porphyrin NO complexes evidenced by magnetic circular dichroism spectroscopy.
abstract: Using magnetic circular dichroism (MCD) spectroscopy together with DFT calculations, the spin density distributions in five-coordinate [Fe(TPP)(NO)] (I) and six-coordinate [Fe(TPP)(MI)(NO)] (II, MI = 1-methylimidazole) are defined. In the five-coordinate complex, a strong Fe-NO sigma bond between pi(*)(h) and d(z)(2) is present that leads to a large transfer of spin density from the NO ligand to Fe(II) corresponding to an electronic structure with noticeable Fe(I)-NO(+) character. Consequently, the MCD spectrum is dominated by paramagnetic C-term contributions. On coordination of the sixth ligand, the spin density is pushed back from the iron toward the NO ligand, resulting in an Fe(II)-NO(radical) type of electronic structure. This is reflected by the fact that the MCD spectrum is dominated by diamagnetic contributions.
authors.affiliation: Institut für Anorganische Chemie, Christian-Albrechts-Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany.
authors.forename: V K K
authors.initials: VK
authors.lastname: Praneeth
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
authors.forename: Nicolai
authors.initials: N
authors.lastname: Lehnert