Superhyperfine splittings,

Transannular interaction via the electron-delocalization mechanism was found, but lessened by 10-15% for the ligand superhyperfine splitting and 30-35% for the hyperfine splitting (62) in the epr spectrum. The crystal structure of [VOS2CNEt2)2] shows that the molecular core has the expected C2V symmetry [V-0 = 159.1(4), V-S = 138.7(2)-241.0(2) pm] (63). Magnetic and spectral data provided evidence for a tetragonal, pyramidal structure (VII) for these complexes. Like many other coordinatively unsaturated, metal... 

The superhyperfine splittings are sufficiently small to ignore second-order effects at X-band, and for adducts of the nitrone compounds splitting from the nitrone-N and the beta-H are the only resolved hyperfine interactions, thus affording the extremely simple resonance condition (cf. Equation 5.10)... 

Oxovanadium(IV) complexes with dithiophosphate ligands have been extensively examined <8,121.161,252,386) x typical ESR spectrum is shown in Fig. 7. In addition to the eight vanadium 1=112 hyperfine lines phosphorus (/ = 1/2) superhyperfine splitting is also observed. The phosphorus superhyper-fine splitting can be considered a bit unusual since the phosphorus is located about 3 A or more away from the metal ion. P and As superhyperfine splitting has been observed in the ESR spectra of ill-defined vanadium phosphine 388) and arsine 389) complexes but in those cases, presumably, direct V-P and V—As interactions occur. ESR parameters have been tabulated for a large number of dithiophosphate 121,252) dithiophosphinate 121.252) complexes. Evaluation 3i) of the fractional 3s character of unpaired electron in dithiophosphate complexes yielded a value of 1.35%. The vanadyl(IV) complexes possess approximate C2V symmetry. The unpaired d electron resides... 

Because of the superhyperfine interaction which arises when the OJ ion is formed on a cation with nonzero nuclear spin (see Section III,A,3) vanadium pentoxide, with 100% naturally abundant5 V isotope (I = ), has been of considerable interest. However, the presence of a superhyperfine splitting has created some difficulty in the assignment of the signals. V205 cannot be prepared with large surface area and most of the data refer to supported V205 systems. 

Magnetic moments (,ueff=1.5 and 1.6 BM for bipy and phen derivatives) confirmed the existence of one unpaired electron and ESR (no 51V- N or 51V-13C superhyperfine splitting) indicated that it is located in a metal orbital. Two strong v(N—O) bands at 1650 and 1520 cm-1 confirm the cis NO groups. 

The 13 C superhyperfine splitting is interpreted in terms of a tram-annular interaction involving the vanadium dxi y orbital and the carbon 2s orbital (581b) (586). 

The EPR spectra of the Mo(Et2 DtcXHNSC6HU)2 have been reported (262, 497). Hydrogen-1, hydrogen-2, and nitrogen-14 superhyperfine splittings were observed (497). 

Some transition metal complexes exhibit HFS due to the ligand this is called superhyperfine splittings (SHFS). Often SHFS are not completely resolved, but contribute to the line width. In such cases isotropic substitution of the ligand nuclei, such as deuterium for hydrogen, can allow the presence of SHFS to be confirmed. 

Similarities with respect to the location of cysteine, histidine and methionine residues in the proteins of azurin, plastocyanin and ceruloplasmin indicate that the type 1 centres in ceruloplasmin are similar to those in the other two proteins. The nine-line superhyperfine splitting in the ESR spectrum of the type 2 Cu has been interpreted in terms of four equivalent nitrogen ligands.978 This was observed in a protein from which the type 1 copper was depleted by dialysis against ascorbate. 

One important feature of Mov intermediate species during enzymatic reaction is the presence of superhyperfine splitting from a proton. Mov model compounds with coordinated N—H groups display superhyperfine coupling of the same order of magnitude as that found in molybdenum enzymes.1002... 

Another type of splitting of the EPR spectrum can occur when an unpaired electron interacts with the nuclei having nonzero I on adjacent atoms. This type of interaction is known as superhyperfine splitting and in an analogous way to hyperfine splitting, the magnitude of the interaction depends on the extent of delocalization of the unpaired electron on the adjacent atoms and the number of bonds involved (Parish, 1990). 

Table 5 A Comparison of H, 170, and 33S EPR Superhyperfine Splittings in the Xanthine Oxidase Very Rapid, Rapid, and Slow Forms with Molybdenum Model Complexes ...

Figure 1. ESR spectrum of galactose oxidase at 5 X I0"4M. T = 100°K, average of six scans. Obtained with Nicolet Lab-80 CAT on a Varian E-9 spectrometer. Insert shows the second and third parallel lines and the five-line superhyperfine splitting.

Figure 4. EPR signal for Mo(S2CN(C2H5)2)(SNHC6-H u)2-displaying proton and nitrogen superhyperfine splitting (92)...

As a fine example of the actual measurement of a parameter matrix asymmetry, we cite the collaborative effort,132 which reported the quantitative measurement via ENDOR of superhyperfine splittings attributed to neighbours of oxygen O contaminative defects (with S = l/2) in x-irradiated BaFBr single-crystals. Here g is anisotropic, and the local symmetry is C2h- While g was taken to be symmetric, the matrix A(19F) required to fit the line-position data was found to be highly asymmetric. ENDOR of course measures NMR transitions by using EPR spectroscopy. 

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