Mdssbauer parameters complexes

To verify this assumption, the temperature dependence of the Mdssbauer parameters (Figs. 21 and 22) were measured for the clathrochelate FeNx3(BOH)2, Fe(4MNx)3(BOH)2, and FeGx3(BOH)2 complexes and their nonmacrocyclic [Fe(H2Nx)3](S04) analog [56]. 

The sTjTe Mdssbauer parameters for the tin-, germanium-, and antimony-capped clathrochelate compounds (Tables 22-24) are typical low-spin iron(II) complexes. The increase in the ligand field strength (a "macrocyclic" effect), causes the increase in s-electron density on the iron nucleus, is less pronounced for these compounds than for their boron-capped analogs experimental ISs are only slightly lower than those calculated from a PIS concept. 

The Fe Mdssbauer parameters for the clathrochelate [FeMn(trom)](BF4) and [Fe2(trom)](BF4) complexes are characteristic of high-spin iron complexes. The spectrum of the [FeMn(trom)](BF4) clathrochelate exhibits one doublet line, which indicates the sole type of coordination centre. The QS value increases regularly with a temperature decrease. A major contribution to the QS value is made by the valence component (the lattice component is small and practically independent of temperature). For [FeMn(trom)](BF4) clathrochelate, all three spin-quintet states are presumably within kT, and the QS value depends on temperature [192]. 

Table 14.16 Iron and tin Mdssbauer parameters for iron-organotin complexes (data at 80 K and values for (Fe) converted from nitroprusside)...

The QS in the Fe Mdssbauer spectra is determined by the geometry of the iron(II) coordination polyhedron and has been utilized to gain information on the structure of the complexes from the spectral parameter vs structure correlation. Conversely, the data available on the structure of clathrochelates employed for working out a modern version of the partial quadrupole splitting (PQS) concept permits one to obtain absolute PQS values and to analyse the results for macrobicyclic complexes [264, 265]. 

Fig. 10. Mdssbauer spectra of reduced (left panels) and oxidized (right panels) PS-I core complex at 80 K (top panels) and 4.2 K (bottom panels), The lower spectrum in each of the left panels was corrected for the unreduced component. The table at top right lists the experimentally determined isomer-shift (IS) and quadrupole-splitting (QS) parameters for oxidized and reduced core complexes at 77 K lower table lists isomer-shift values reported in the literature for other [4Fe 4S] and [2Fe 2S] clusters. Data source Petrouleas, Brand, Parrett and Golbeck (1989) A Mossbauer analysis of the low-potential iron-sulfur center in photosystem I Spectroscopic evidence that Fx is a [4Fe-4S] cluster. Biochemistry 28 8982.

Often, the observed iron-57 Mossbauer spectral hyperfme parameters, when combined with a knowledge of the magnetic properties of the complexes, can easily lead to an unambiguous assignment of the iron oxidation state, coordination number, and yield the extent of the distortion of its coordination environment. The same is also true for many of the other Mdssbauer nuclides mentioned above. 

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