X-Band Pulsed ENDOR Study of57Fe-Substituted Sodalite— The Effect of the Zero-Field Splitting

Studies of Fe(III) incorporated into AlPO4-20 by X- and W-band EPR spectroscopies

“…Taking The presence of a distribution of species with varying D and E values was also supported by spectral simulations of the temperature-dependent spectra, using perturbation theory. 31 Simulations were carried out using both Lorentzian (dotted line, Fig. 7) and Gaussian (dashed line) lineshapes.…”

“…The ZFS parameters (D and E) and the values of the 57 Fe isotropic hyperfine coupling were determined from orientation-dependent X-band 57 Fe ENDOR spectra through simulations. 31 The EPR and the ENDOR signals of FeSOD showed that the ZFS interaction of framework Fe(III) in this structure was much smaller than in Fe-LTL, Fe-Mazzite and Fe-ZSM-5, indicating minimal distortion of the tetrahedral sites in sodalite. 31,43 The question that arises is whether this is a unique property of the highly symmetric sodalite structure.…”

“…31 The EPR and the ENDOR signals of FeSOD showed that the ZFS interaction of framework Fe(III) in this structure was much smaller than in Fe-LTL, Fe-Mazzite and Fe-ZSM-5, indicating minimal distortion of the tetrahedral sites in sodalite. 31,43 The question that arises is whether this is a unique property of the highly symmetric sodalite structure. In order to obtain a better understanding of the factors that affect the distortion of the tetrahedral sites, and explore how they are expressed in the EPR characteristics of the Fe(III) centers, we investigated the incorporation of Fe(III) into zeolites with the sodalite structure, but with different compositions.…”

“…42 In addition, high order frequency shifts due the presence of the ZFS and a relatively large hyperfine coupling, which lead to broadening of the ENDOR spectrum in orientationally disordered samples, are significantly reduced. 31,43 At low temperatures, the larger difference in the Boltzmann populations of the different M S levels is helpful in reducing the number of observed EPR transitions and in determining the sign of the ZFS interaction. 43,44 Another advantage, which is technically relevant to pulse experiments, is the significant reduction in the spectrometer dead time.…”

“…The incorporation of Fe(III) into a number of aluminosilicate zeolites has been recently studied by X-and W-band pulsed EPR and ENDOR. 18,31,43,46 The simplest EPR spectrum, characteristic of a single Fe(III) species with a relatively narrow signal centered at g ³ 2, was observed for Fe-sodalite (FeSOD; Si/Al D 1, Fe/Al D 0.001) at both frequencies and assigned to a framework T site. The ZFS parameters (D and E) and the values of the 57 Fe isotropic hyperfine coupling were determined from orientation-dependent X-band 57 Fe ENDOR spectra through simulations.…”