title: On the feasibility of N2 fixation via a single-site FeI/FeIV cycle: Spectroscopic studies of FeI(N2)FeI, FeIV[triple bond]N, and related species.
abstract: The electronic properties of an unusually redox-rich iron system, [PhBP(R)3]Fe-Nx (where [PhBP(R)3] is [PhB(CH2PR2)3]-), are explored by Mössbauer, EPR, magnetization, and density-functional methods to gain a detailed picture regarding their oxidation states and electronic structures. The complexes of primary interest in this article are the two terminal iron(IV) nitride species, [PhBP(iPr)3]Fe[triple bond]N (3a) and [PhBP(CH2Cy)3]Fe[triple bond]N (3b), and the formally diiron(I) bridged-Fe(mu-N2)Fe species, {[PhBP(iPr)3]Fe}2(mu-N2) (4). Complex 4 is chemically related to 3a via a spontaneous nitride coupling reaction. The diamagnetic iron(IV) nitrides 3a and 3b exhibit unique electronic environments that are reflected in their unusual Mössbauer parameters, including quadrupole-splitting values of 6.01(1) mm/s and isomer shift values of -0.34(1) mm/s. The data for 4 suggest that this complex can be described by a weak ferromagnetic interaction (J/D < 1) between two iron(I) centers. For comparison, four other relevant complexes also are characterized: a diamagnetic iron(IV) trihydride [PhBP(iPr)3]Fe(H)3(PMe3) (5), an S = 3/2 iron(I) phosphine adduct [PhBP(iPr)3]FePMe3 (6), and the S = 2 iron(II) precursors to 3a, [PhBP(iPr)3]Fe-Cl and [PhBP(iPr)3]Fe-2,3:5,6-dibenzo-7-aza bicyclo[2.2.1]hepta-2,5-diene (dbabh). The electronic properties of these respective complexes also have been explored by density-functional methods to help corroborate our spectral assignments and to probe their electronic structures further.
authors.affiliation: Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA 15213, USA. hendrich@andrew.cmu.edu
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hendrich
authors.forename: William
authors.initials: W
authors.lastname: Gunderson
authors.forename: Rachel K
authors.initials: RK
authors.lastname: Behan
authors.forename: Michael T
authors.initials: MT
authors.lastname: Green
authors.forename: Mark P
authors.initials: MP
authors.lastname: Mehn
authors.forename: Theodore A
authors.initials: TA
authors.lastname: Betley
authors.forename: Connie C
authors.initials: CC
authors.lastname: Lu
authors.forename: Jonas C
authors.initials: JC
authors.lastname: Peters
mesh_terms: D003198:Computer Simulation; D007501:Iron / Q000737:chemistry*; D009586:Nitrogen Fixation; D013057:Spectrum Analysis
chemical_list: D007501:Iron