57Fe Mossbauer spectra

Figure 2. Relative amounts of various iron species deduced from 57Fe Mossbauer spectra of the Fe-exchanged samples shown in relation to the progress of the hydrothermal crystallization process at 80°C (A), 57Fe Mossbauer spectra of the Fe-exchanged samples after 0 (a), 120 (b), 180 (c) and 240 min (d) of the hydrothermal crystallization process at 80°C (B) and RBS spectra collected on five different particles of the sample crystallized for 240 min (C). The position of surface Fe in Fig. 2C is marked by the vertical arrow. Depth scale (depth into each particle) is increasing toward left (marked with the horizontal arrow). Fit to experimental data with assumed homogeneous depth distribution of Fe is marked with the continuous line.

It has been postulated that the origin of the two different high-spin Fe(II) doublets observed in the 57Fe Mossbauer spectra may be that a small fraction (about 6%) of the Fe(II) ions experience a different local environment, most likely in the distribution of the non-coordinating solvent and anion molecules, from that of the majority of the high-spin Fe(II) ions. 

Fig. 9 57Fe Mossbauer spectra of (bt, S) recorded at 4.2 K in zero-field (a) and in a magnetic field of 50 kOe (b). 57Fe Mossbauer spectra of (bpym, S) recorded at 4.2 K in zero-field (c) and in a magnetic field of 50 kOe (d). 57Fe Mossbauer spectra of (bpym, Se) recorded at 4.2 K in zero-field (e) and in a magnetic field of 50 kOe (f). LS in [HS-LS] and [LS-LS] pairs (grey), HS in [HS-LS] pairs (light grey), HS in [HS-HS] pairs (dark grey) (adapted from [11])...

Fig. 11 57Fe Mossbauer spectra of (bt, S) recorded at 4.2 K in zero-field before irradiation (a), immediately after irradiation (b), 6 days (c) and 11 days (d) after irradiation. Mossbauer subspectra correspond to HS species (grey), LS species (dark grey)...

The 57Fe Mossbauer spectra for [FexCo x(acpa)2]BPh4 (x=0.035 and 0.074) show that the transition has been displaced to a higher temperature than that for the pure Fe(III) compound [156]. This may again be related to... 

Solid [Fe(salacen)(l-methyl-imidazole)2]C104 displays a relatively complete, gradual spin crossover [180]. Measurements of both 57Fe Mossbauer spectra and magnetism indicate that the transition observed in the one-dimensional polymeric system [Fe(salacen)(l,l -tetramethylenediimidazole)] C104 is also gradual but incomplete at both 290 K (/ze/j=5.37 B.M.) and 4.2 K (Heff=337 B.M.) [180],... 

The inter-conversion of the spin states in many instances is so rapid that the separate contributions to the 57Fe Mossbauer spectra are not resolved. Thus this technique, which has proved so diagnostic in iron(II) systems, is frequently less suited to the derivation of spin transition curves for iron(III). A further corollary of the faster spin state inter-conversion is the rarity of the LIESST effect among iron(III) systems, in contrast to its ubiquitous occurrence in iron(II). 

Reaction of FeCo2(CO)9S with a series of phosphines (31, 133) and isocyanides (126) yielded mono-, di-, and trisubstituted derivatives, Eqs. (77) and (78). 57Fe-Mossbauer spectra of the phosphine-substituted derivatives indicated that substitution at cobalt occurs prior to substitution at iron (31). Unfortunately, no crystallographic evidence has been obtained for any of these derivatives, and the precise stereochemistry has not been resolved, even with the aid of l3C-NMR spectra (9). The problem is compounded with the isocyanide ligands since several isomers of the trisubstituted derivatives are formed. 

The magnetic ordering was also monitored via 57Fe Mossbauer spectra at 4.2 and 295 K. The four crystallographically independent iron sites could be distinguished in the Mossbauer spectra. The isomer shifts at 4.2 and 295 K are similar for the four iron sites. As expected, the hyperfine fields detected at the iron nuclei are about 20% larger at 4.2 K. They range between 23.5 and 36.3 T. 

From variable-temperature 57Fe Mossbauer spectra Konig and Ritter82) determined the Debye-Waller factors f over the temperature range of 298-4.2 K in III (on polymorph one with 0.9 B.M. at 77 K). Whereas the magnetic moment and other physical properties show an abrupt change with temperature near Tc ( 213 K), they found a continuous change of -Inf. 

Fig. 19. 57Fe Mossbauer spectra of [Fe(2-pic)3]Cl2 EtOH at various temperatures84 ...

---