title: Characterization of three members of the electron-transfer series [Fe(pda)2]n (n=2-, 1-, 0) by spectroscopy and density functional theoretical calculations [pda=redox non-innocent derivatives of N,N'-bis(pentafluorophenyl)-o-phenylenediamide(2-, 1.-, 0)].
abstract: The four-coordinate iron complexes, [Fe(III)(pda(2-))(pda(.-))] (1) and [AsPh(4)](2)[Fe(II)(pda(2-))(2)] (2) were synthesized and fully characterized; pda(2-) is the closed-shell ligand N,N'-bis(pentafluorophenyl)-o-phenylenediamido(2-), and pda(.-) represents its one-electron-oxidized pi-radical anion. Single-crystal X-ray diffraction studies of 1 and 2 performed at 100(2) K reveal a distorted tetrahedral coordination environment at the iron centers, as a result of the intramolecular pi-pi interactions between C(6)F(5) rings. The electronic structures of 1 and 2 were unambiguously determined by a combination of (57)Fe Mössbauer and electronic spectroscopy, magnetic susceptibility measurements, X-ray crystallography, and DFT calculations. Compound 1 contains an intermediate-spin Fe(III) ion (S(Fe)=3/2) strongly antiferromagnetically coupled to a pi-ligand radical (S(R)=1/2) yielding an S(t)=1 ground state. Complex 2 possesses a high-spin Fe(II) center (S(Fe)=2) with two closed-shell dianionic ligands. Complexes 1 and 2 are members of the redox series [Fe(pda)(2)](n) with n=0 for 1 and n=2- for 2. The anion n=1- has been reported previously in the coordination salt [Fe(dad)(3)][Fe(pda)(2)] (3; dad=N,N'-bis(phenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene). A complicated temperature-dependent electronic structure has been observed for this salt. Here, DFT calculations performed on 3 confirm the previous assignments of spin- and oxidation-states. Thus, [Fe(pda)(2)](n) (n=0, 1-, 2-) constitutes an electron-transfer series, which has also been established by cyclic voltammetry; the mono- and dications (n=1+ and 2+) are also accessible in solution, but have not been further investigated. The (57)Fe Mössbauer spectra of [Fe(pda)(2)](n) species in 1 and 3 show extremely large quadrupole splitting constants due to addition of the valence and covalence contributions that have been confirmed by DFT calculations.
authors.affiliation: Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany. marik@mpi-muelheim.mpg.de
authors.forename: Marat M
authors.initials: MM
authors.lastname: Khusniyarov
authors.forename: Eckhard
authors.initials: E
authors.lastname: Bill
authors.forename: Thomas
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: Eberhard
authors.initials: E
authors.lastname: Bothe
authors.forename: Klaus
authors.initials: K
authors.lastname: Harms
authors.forename: Jörg
authors.initials: J
authors.lastname: Sundermeyer
authors.forename: Karl
authors.initials: K
authors.lastname: Wieghardt
mesh_terms: D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004159:Diphenylamine / Q000031:analogs & derivatives* / Q000737:chemistry; D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D005290:Ferric Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D008280:Magnetics; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D015204:Spectroscopy, Mossbauer / Q000379:methods; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013696:Temperature
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D004159:Diphenylamine