title: Normal-mode analysis of FeCl4- and Fe2S2Cl42- via vibrational mössbauer, resonance Raman, and FT-IR spectroscopies.
abstract: [NEt(4)][FeCl(4)], [P(C(6)H(5))(4)][FeCl(4)], and [NEt(4)](2)[Fe(2)S(2)Cl(4)] have been examined using (57)Fe nuclear resonance vibrational spectroscopy (NRVS). These complexes serve as simple models for Fe-S clusters in metalloproteins. The (57)Fe partial vibrational density of states (PVDOS) spectra were interpreted by computation of the normal modes assuming Urey-Bradley force fields, using additional information from infrared and Raman spectra. Previously published force constants were used as initial values; the new constraints from NRVS frequencies and amplitudes were then used to refine the force field parameters in a nonlinear least-squares analysis. The normal-mode calculations were able to quantitatively reproduce both the frequencies and the amplitudes of the intramolecular-mode (57)Fe PVDOS. The optimized force constants for bending, stretching, and nonbonded interactions agree well with previously reported values. In addition, the NRVS technique also allowed clear observation of anion-cation lattice modes below 100 cm(-1) that are nontrivial to observe by conventional spectroscopies. These features were successfully reproduced, either by assuming whole-body motions of point-mass anions and cations or by simulations using all of the atoms in the unit cell. The advantages of a combined NRVS, Raman, and IR approach to characterization of Fe-S complexes are discussed.
authors.affiliation: Department of Applied Science, University of California, Davis, 95616, USA.
authors.forename: Matt C
authors.initials: MC
authors.lastname: Smith
authors.forename: Yuming
authors.initials: Y
authors.lastname: Xiao
authors.forename: Hongxin
authors.initials: H
authors.lastname: Wang
authors.forename: Simon J
authors.initials: SJ
authors.lastname: George
authors.forename: Dimitri
authors.initials: D
authors.lastname: Coucouvanis
authors.forename: Markos
authors.initials: M
authors.lastname: Koutmos
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sturhahn
authors.forename: Ercan E
authors.initials: EE
authors.lastname: Alp
authors.forename: Jiyong
authors.initials: J
authors.lastname: Zhao
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Cramer
mesh_terms: D000465:Algorithms; D058085:Iron Compounds / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D015204:Spectroscopy, Mossbauer; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics
chemical_list: D058085:Iron Compounds; D008667:Metalloproteins