Superhyperfine spectra

Superhyperfine spectra due to electron-nuclear coupling are often more easily obtained by recording and transforming the electron... 

The deoxygenation of solutions of irradiated silsesquioxanes, e.g. in C2CI4, led to very well resolved EPR spectra (Fig. 3). Linewidths (Afipp) in solution were in the range of 0.002-0.009 mT, whereas in solids linewidths of about 0.10-0.15 mT were observed. The spectral patterns can be accounted for quantitatively by weighted addition of the theoretically expected superhyperfine spectra of H trapped in SigOn isotopomers possessing no Si (68.2 %), one Si (26.7 %) or two Si nuelei (4.6 %) respectively (see Table 1). 

Several papers deal with the solvation, coordination and redox behaviour of various metal complexes, especially of copper, in different ILs. The cationic complexes of [Cu(acac)(bipy)]Cl and [Cu(acac)(phen)]Cl, (acac = acelylacetonate, bipy=2,2 -bipyridine, phen = 1,10-phenanthro-line) were studied in ILs and well-resolved superhyperfine spectra obtained. The corresponding spin Hamiltonians suggest a square pyramidal structure including coordination of the anion of the IL. 

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... 

F superhyperfine couplings in the axially symmetric frozen solution spectrum [ReNF4] showing two pairs of sextets in parallel and perpendicular part. 

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... 

The range of the gzz values is shown clearly by a comparison of the results for the NaY and NaX zeolites. Since the migration of Na+ ions is related to the presence of water (76), it is likely that the type of precursor (Na4)4+ -(H20)x complex formed after a proper degree of dehydration (278) will be strongly dependent on the pretreatment conditions. This will be reflected in the gzz values of the OJ produced during y irradiation by electron transfer from the precursor (278). It is also likely that the OJ can migrate after its formation as shown by Kasai and Bishop (264). These authors (272) have detected a superhyperfine interaction from Na nuclei (I = ) in the EPR spectrum of OJ formed in Na-reduced NaY zeolite and characterized by gzz = 2.113. This value is very close to those observed for alkalisuperoxides trapped in krypton matrices (Ref. 44, Appendix A). 

When ScY zeolite, pretreated at 500°C, is y-irradiated in the presence of oxygen and then heated at 150°C, an EPR spectrum is observed with g values of 2.030, 2.009, and 2.002 which is characteristic of OJ adsorbed at Sc3+ ions, assuming an ionic model. This assignment was confirmed by the observation of an eight-line superhyperfine structure with Azz = 5.7, Ayy = 4.4, and Axx = 5.1 G characteristic of the interaction with 45Sc (/ = ) (103). 

However, it must be borne in mind that in previous work, H2 did not react with a triangular array of O ions to form OH" ions (354). If such a reaction with H2 occurred, then the O" ions would no longer be available for Oj formation. Moreover, the reaction of pairs of O ions with oxygen should lead to pairs of O J ions which would have an abnormal EPR spectrum if they can be seen at all. In fact, the g tensor is as expected for isolated OJ ions. The CoO-MgO system behaves as CaO for the formation of Oj, i.e., via invisible O ions. The ozonide ions characterized by a three-g-value EPR signal (2.0025, 2.012, 2.017) do not exhibit any superhyperfine interaction with cobalt nuclei, suggesting that they are adsorbed on Mg2+ ions (110). Depending on the system (MgO, CaO, CoO-MgO) and the experimental conditions, the ozonide ion Oj disappears irreversibly between 25° and 130°C. In the case of MgO (333,334), OJ ions are formed when O J ions are destroyed, whereas for CaO (158) and CoO-MgO (110) the evidence is not clear. 

The EPR spectrum of VO(Et2Dtc)2, enriched with 13C at the CS2 group of the E2Dtc ligand, shows13C superhyperfine interactions. 

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. 

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). 

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.

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