Paramagnetic parameters

To study further the nature of the coordinated 02 molecule, adsorption experiments with 170180 were carried out. Figure 3 shows an EPR spectrum of the ammoniated Co(II)Y zeolites, treated with 170180. Since the nuclear spin of 170 is 5/2, paramagnetic species with one 170 have 21 + 1 or six lines. Two sets of six hyperfine lines (170180) can be observed in addition to the cobalt hyperfine lines. The paramagnetic parameters of 170 species are given in Table II. These values, including the g tensor, are comparable with those observed in several studies of the superoxide ion on various oxides (15). 

Most silyl radical studies to date provide electron paramagnetic parameters with g-values in the range 2.0003-2.0053, depending on substitution, and 29Si hyperfine splitting (hfs) constants a(a-2>>S ) in the range 6.4-49.8 mT1. These values correlate well with the... 

There are several books to which one can refer for more detailed technical information but, in general, chemical shifts for heavy and/or quadrupolar nuclei are rationalized on the basis of the Ramsey expression, equation (l) 5- 8 jqj. overall shielding (cr), made up of diamagnetic (oj) and paramagnetic (electron density in the immediate... 

Data for which no reference is given are from the Slrukturbericht of P. P. Ewald and C. Hermann. 6 R. W. G. Wyckoff, Z. Krisl., 75,529 (1930). W. H. Zachariasen, ibid., 71, 501, 517 (1929). d The very small paramagnetic susceptibility of pyrite requires the presence of electron-pair bonds, eliminating an ionic structure Fe++S2. Angles are calculated for FeS2, for which the parameters have been most accurately determined. The parameter value (correct value = 0.371) and interatomic distances for molybdenite are incorrectly given in the Slrukturbericht. 

Theory and Applications of Molecular Paramagnetism," Wiley-Interscience, New York, NY (1976). [These give a detailed discussion and factors for converting the classical Gaussian cgs-emu parameters to the mksA S.I. units.] Note ... 

The ESR measurements were made at RT or 77 K on a Varian E-9 spectrometer (X-band), equipped with an on-line computer for data analysis. Spin-Hamiltonian parameters (g and A values) were obtained from calculated spectra using the program SIM14 A [26]. The absolute concentration of the paramagnetic species was determined from the integrated area of the spectra. Values of g were determined using as reference the sharp peak at g = 2.0008 of the E i center (marked with an asterisk in Fig. 3) the center was formed by UV irradiation of the silica dewar used as sample holder. 

Fig. 9.21 NFS spectra of the paramagnetic picket-fence porphyrin complex [ Fe(CH3COO) (TPpivP)] obtained at 3.3 K in a field of 6.0 T applied (a) perpendicular to both the synchrotron beam and the polarization vector of the radiation and (b) perpendicular to the synchrotron beam but parallel to the polarization vector of the radiation. The solid lines are simulations with the SYNFOS program using 5 = 2 and parameters described in the text. (Taken from [13])...

However, when it comes to the simulation of NFS spectra fi om a polycrystalline paramagnetic system exposed to a magnetic field, it turns out that this is not a straightforward task, especially if no information is available from conventional Mossbauer studies. Our eyes are much better adjusted to energy-domain spectra and much less to their Fourier transform therefore, a first guess of spin-Hamiltonian and hyperfine-interaction parameters is facilitated by recording conventional Mossbauer spectra. 

In the case of paramagnetic complexes their experimental magnetic parameters are determined by computer simulation of the powder spectra [59], Together with the corresponding calculated values, obtained using a relativistic spin-unrestricted ZORA approach, they all are collected in Table 2.8. 

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