Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering

Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations

DFT normal coordinate analysis of the vibrational spectra of iron and germanium corroles

DFT calculations on the vibrational modes of [FeCl(OECorr)], [FeCl(TPCorr)], [FeC6H5(OECorr)] and the corresponding germanium systems, [GeCl(OECorr)], [GeCl(TPCorr)] and [GeC6H 5(OECorr)] are for the first time presented. In addition DFT calculations on the electronic structure of the germanium corroles are given (OECorr, octaethylcorrole; TPCorr, triphenylcorrole). B3LYP functional and the 6-311G basis are used for the H, C and N atoms while for iron and germanium the Wachters-Hay double-¿ basis as implemented in the program package Gaussian 98 is applied. The normal modes of vibrations are calculated for geometries, obtained by optimizations on the theoretical potential energy surfaces. The formation of a ¿-cation corrole radical in the cases of [FeCl(OECorr)] and [FeCl(TPCorr)] is confirmed by the downshift of some C-C corrole skeletal modes compared to [GeCl(OECorr)] or [GeCl(TPCorr)], respectively. The largest shifts are derived for vibrations with high C¿-Cmeso, C¿-C¿ as well as C¿-C ß eigenvectors. Also the Cß-Cß valence frequencies show a downshift in cases when the Cß-C ß bonds stretch and contract in phase. The downshifts of some C-C stretchings in the phenyl axial ligand of the [FeC6H 5(OECorr)] provide evidence for an electron flow from the axial ligand to iron. Simulated nuclear inelastic scattering (NIS) spectra are generated by using the calculated normal modes. High intensity of the bands, connected with substantial contributions to the mean square displacements of the iron nucleus, is associated with in-plane equatorial iron modes, namely the Fe-N stretching

Is the corrolate macrocycle innocent or noninnocent? Magnetic susceptibility, Mossbauer, H-1 NMR, and DFT investigations of chloro- and phenyliron corrolates

an attempt to determine the electron configuration of (anion)iron corrolates, i.e., whether they are S = 1 Fe(IV)-corrolate(3(-)) or S = (3)/(2) Fe(III)-corrolate(2(-.)), with antiferromagnetic coupling between the iron and macrocycle electrons to yield overall S = 1, two axial ligand complexes of an iron octaalkylcorrolate have been studied by temperature-dependent magnetic susceptibility, magnetic Mossbauer, and H-1 NMR spectroscopy, and the results have been compared to those determined on the basis of spin-unrestricted DFT calculations. Magnetic susceptibility measurements indicate the presence of a noninnocent macrocycle (corrolate (2-(.))) for the chloroiron corrolate, with strong antiferromagnetic coupling to the S = (3)/(2) Fe(III) center, while those for the phenyliron corrolate are not conclusive as to the electron configuration. Temperature- and field-dependent Mossbauer spectroscopic investigations of these two complexes yielded spectra that could be simulated with either electron configuration, except that the isomer shift of the phenyliron complex is -0.10 mm/s while that of the chloroiron complex is +0.21 mm/s, suggesting that the iron in the former is Fe(IV) while in the latter it is Fe(III). 1H NMR spectroscopic studies of both axial ligand complexes show large negative spin density at the meso carbons, with those of the chloroiron complex (Cal, S.; Walker, F. A.; Licoccia, S. Inorg. Chem. 2000, 39, 3466) being roughly four times larger than those of the phenyliron complex. The temperature dependence of the proton chemical shifts of the phenyliron complex is strictly linear. DFT calculations are consistent with the chloroiron complex being formulated as S-1 = (3)/(2) Fe(III)-corrolate (2(-.)) S-2 = (1)/(2), with negative spin density at all nitrogens and meso carbons, and a net spin density of -0.79 on the corrolate ring and positive spin density (+0.17) on the chloride ion and +2.58 on the iron. In contrast, the phenyliron complex is best formulated as S = I Fe(IV)-corrolate (3-), but again with negative spin density at all nitrogens and meso carbons of the macrocycle, yet with the net spin density on the corrolate ring being virtually zero; the phenyl carbanion carbon has relatively large negative spin density of -0.15 and the iron +2.05. On the basis of all of the results, we conclude that in both the chloroiron and phenyliron complexes the corrolate ring is noninnocent, in the chloroiron complex to a much larger extent than in the phenyliron complex

Not innocent : verdict from ab initio multiconfigurational second-order perturbation theory on the electronic structure of chloroiron corrole

From a suitably broad perspective, transition metal corroles may be viewed as stable, synthetic analogues of high-valent heme protein intermediates such as compounds I and II. Against this backdrop, the electronic structure of chloroiron corrole has provoked a lively debate in recent years. Thus, whereas NMR spectroscopy and DFT calculations suggest an S = 3/2 Fe(III) corrole(center dot 2-) radical description, certain researchers have favored an Fe(IV) formulation. These two descriptions are indistinguishable as far as DFT calculations are concerned. Ab initio CASSCF/CASPT2 calculations provide unambiguous support for the former description. In addition, they rule out any Fe(IV) state, whether high- or low-spin, within 1.5 eV of the ground state