Ferrates IV, V, and VI

Room-temperature Mossbauer spectra of ferrate(V) during the decomposition process. A doublet of ferrate(IV) and central lines of a-Fe and KFe02 are also shown. (Reproduced from Ref. 21 with permission of Springer.) 

Recently, iron(V) nitride complex [PhB( Bulm)3Fe =N]BArF24 (PhB( Bulm)3 = phenyltris(3-tert-butylimidazol-2-ylidene)borato BArp24 = B(3,5-(CF3)2QH3)4 ) has been prepared [100]. This complex has a four-coordinate iron ion with a terminal nitride ligand. The characterization of the complex by Mossbauer and electron paramagnetic resonance spectroscopy demonstrated d iron(V) metal center in a low-spin (S= 1/2) electron configuration. The decomposition of the complex by water at low temperature formed ammonia and iron(ll) species. 

Most of the Mossbauer spectra were collected on salts of ferrate(VI) (Table 24.2). Table 24.2 demonstrates that isomer shifts of different compounds of ferrate(VI) vary very little (—0.87 to —0.91 mms ). This indicates a weak influence of the counterions on iron bound in an oxygen tetrahedron, which is the main structural unit of all ferrates(VI). In recent years, hyperfine parameters of K2Fe04 at very low temperature (1.5-5 K) with and without external magnetic field have been determined (Table 24.3) [101]. Results of Table 24.3 Indicate that the magnetic ordering temperature is 

TABLE 24.3 Hyperfine Parameters and Relative Spectrum Areas of the Mossbauer Spectra of the Potassium Ferrate(VI) Sample  

Reproduced from Ref. 101 with permission from the American Chemical Society. T is the temperature of measurement, is the external magnetic 

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Decomposition of potassium ferrate(VI) at 1000 K gives a fer-rate(V), K3Fe04, and several types of ferrateflV), for example FeO, Fe04 are known these ferrates(IV) have no solution chemistry and are probably best regarded as mixed oxides, since the Fe04 ion has no identifiable structure. 

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