The Mössbauer Effect and its Significance in Chemistry

Abstract

Resonance fluorescence of recoil-free y-rays from atomic nuclei dcywnd.s on the state of the chemical bonding of the atoms. The latter influences ihr position of' the energy level of the atomic nuclei, so that the energy required f ;~ exciiulion yf' resonance fluorescence is somewhat smaller or greater than the energy ofthe y-quanta r m i t t d by the radiation source. In order to obtain resonance fluorescence, therejorc, the radiation source and absorber have to be kept moving relative to each other. I f the inlensity yf thc rrsonance fluorescence is plotted akgainst this relative velocity, Miissbauer spectra are ohtainrd. The positions of the lines in these spectra make it possible to draw conclusions about the nature of the atom's bonds. The efficiency of this method is demonstrated by illustration with numerous iron compoundr. It was shown, jbr instance, that thc iron atoilis in "insoluble Prussian B k " have well-defined oxidation levels. "Turnbitll's Bhie'' shows ihe identical spectrum. A structure could be ascribed to lri-iron dodccacarhonyl that also cxplains the diama<zpetism of the compound.A set-up for observing resonance nuoicscence is shown diagrammatically in Figure l . It consists of a radiation source Q, the absorber A, and the detectors I and 11, which serve to determinc the intensity cf the riidiation. One detector is placed in the radiation beam, thc second is placed perpendicul;irly t o it. Unless thc energy o f the light quanta emitted by the radiation source corresponds to the energy of the first excited state of the clectron shell or absorber A, no resonance fluorescer.cc occurs, in accordancc with the above explanations. Detector I will then indicatc the full intensity passing

The First Example of a True “Turnbull’s Blue” Family Compound with Trapped Iron Oxidation States

“…The absence of such interactions and trapping of iron oxidation states in the cations and anions was demonstrated by X-ray diffraction and magnetic susceptometry. Magnetic measurements are consistent with diamagnetic Fe II inside the macrocyclic moieties and S = 1/2 for Fe III 6 ] 3Ϫ has never been reported. Detailed examination of PB's molecular and electronic structures suggest a significant exchange interaction between ions, and valence delocalization [1,10,12,13] along the FeϪCϵNϪFe bonds.…”

“…The reaction of [Fe( [9]ane-S 3 ) 2 ](ClO 4 ) 2 with K 3 [Fe(CN) 6 ] in aqueous solution in molar ratio 3:2 results in precipitation of shiny ruby colored crystals of product, while the color of the solution changes to dull yellow. If the reaction mixture is allowed to stand for several days an additional amount of product forms, along with a minor amount of classic PB colloid.…”

“…The Prussian Blue synthesis heralded not only the discovery of a new family of cyanides, but initiated a whole field of coordination chemistry. Prussian Blue was ascribed as being the iron(III) hexacyanoferrate(II), Fe 4 [Fe(CN) 6 ] 3 , in contrast to the similarly intense blue pigment Turnbull's Blue. Recently [1Ϫ3] all these various iron cyanides have been consolidated into a single family of Prussian Blues (PB's).…”

“…In this paper we use this name solely in reference to iron-containing cyanoferrates. Only since the 1960s have the identities of Prussian (Fe 4 [Fe(CN) 6 ] 3 ) and Turnbull's Blues (''Fe 3 [Fe(CN) 6 ] 2 '') been elucidated by magnetochemistry and Mössbauer spectroscopy. [2,4Ϫ10] These methods, as well as subsequent X-ray examination [11] revealed that Prussian Blue and Turnbull's Blue are both iron(III) hexacyanoferrates(II), leptic thioether environment plays the dual role of stabilizing Fe II and protecting the central metal ion from direct bridging with hexacyanoferrate(III) anions.…”

Electronic State of Iron Complexes in the Interlayer of Hydrotalcite-Like Materials

“…The materials before the anion exchange had been obtained at pHs of (a) 8.5, (b) 10.0, (c) 11.0, and (d) 13.0 in their preparation stages. ferrate(III), although both values are close to the upper ends of the groups (Fluck et al, 1963).…”