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  • Title: Normal-mode analysis of FeCl4- and Fe2S2Cl42- via vibrational mössbauer, resonance Raman, and FT-IR spectroscopies.
    Author: Smith MC, Xiao Y, Wang H, George SJ, Coucouvanis D, Koutmos M, Sturhahn W, Alp EE, Zhao J, Cramer SP.
    Journal: Inorg Chem; 2005 Aug 08; 44(16):5562-70. PubMed ID: 16060605.
    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.
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