G. Michael Bancroft

Applications of the Mössbauer effect to silicate mineralogy—II. Iron silicates of unknown and complex crystal structures

Abstract Measurements have been made of the Mossbauer spectra of howieite, deerite and two sapphirines, for which the crystal structures are unknown and zussmanite and the alkali amphibole crocidolite. Computer analyses of the spectral data for each silicate have yielded values for the chemical shift and quadrupole splitting for each doublet in the Mossbauer spectra. These parameters are correlated with those for iron ions in silicates of known crystal structures to give information on the oxidation state, electronic configuration, and co-ordination site of each iron atom in the structures. High spin iron is found in all minerals studied. All minerals except one sapphirine contain at least one structurally distinct type of Fe2+ ion in sixfold co-ordination, while deerite contains Fe2+ ions in fourfold co-ordination. Howieite, deerite, and crocidolite contain Fe3+ in sixfold co-ordination, while sapphirines contain Fe3+ in fourfold co-ordination. Computer calculated areas in the Mossbauer spectra have been used to estimate the fraction of each iron species in a structure giving rise to absorption, assuming that the area under a peak is directly proportional to the amount of iron in a site. The results for Fe2+ and Fe3+ containing minerals agree well with chemical analysis values. The area data has allowed Fe2+ site populations to be determined in the crocidolite structure.

Additive model for 119Sn Mössbauer quadrupole splitting in five-co-ordinate organotin(IV) compounds

Mossbauer parameters are reported for ten cationic organotin(IV) complexes of type [R3SnL2][BPh4](R = alkyl or phenyl, L = electrongegative ligand). Details are given of a regression method which is used to distinguish structural isomers of trigonal-bipyramidal [R3SnL2] species by their 119Sn quadrupole splittings. By use of new and literature data, partial quadrupole splitting (p.q.s.) parameters are calculated for a variety of ligands in trigonal-bipyramidal structures. Comparison of theory with experiment indicates that the additive model gives a consistent account of the relationship between quadrupole splitting and stereochemistry in trigonal-bipyramidal organotin(IV) compounds. The 119Sn parameters are used to calculate p.q.s. parameters for 121SbV, thus extending recent work on application of the additive model to five-co-ordinate organoantimony(V) compounds.

Mössbauer Spectrum of Fe2+ in a Square‐Planar Environment

The Mossbauer spectrum of high‐spin Fe2+, square planar coordinated by oxygens in BaFeSi4O10, has been studied in the temperature range 80°—650°K. The spectrum, a quadrupole doublet, was analyzed by computer fitting, and the results statistically tested using the concept of internal and external consistency. Quadrupole splitting and center shift data are reported for the whole range 80°—650°K, and the widths and relative intensities of the lines have been measured at 80° and 295°K. The quadrupole splitting has been successfully correlated with the magnetic susceptibility and electronic spectrum of Fe2+ in BaFeSi4O10. The lattice contribution is found to be slightly larger in magnitude than the valence contribution, and of opposite sign. By studying both randomized and oriented samples the sign of the quadrupole splitting has been determined experimentally, and the anisotropy of the recoil‐free fraction measured. The temperature variation of the center shift has been analyzed in terms of the second‐order D...

Mössbauer studies of electron spin relaxation and radiolytic effects in diluted tris(acetylacetonato) FeIII

The Mossbauer spectra of tris(acetylacetonato)iron(III), [Fe(AcAc)3] diluted in tris(acetylacetonato)aluminium(III), [Al(AcAc)3] and tris(acetylacetonato)gallium(III), [Ga(AcAc)3] have been obtained at room temperature and 110 K. The linewidth broadening observed in these spectra is temperature and concentration dependent. This line broadening phenomenon is attributed to paramagnetic spin relaxation. The resolved hyperfine structures at 4.2 K for the 1 wt % Fe(AcAc)3 in (Fe.Al)(AcAc)3 sample are consistent with this interpretation.Irradiation of the diluted Fe(AcAc)3 samples with 60Co γ rays at room temperature leads to a decrease in the Fe(AcAc)3 Mossbauer line widths, and FeII peaks at low Fe(AcAc)3 concentrations in the Al(AcAc)3 matrix. These observations are consistent with a motional narrowing mechanism proposed earlier. The results are discussed in terms of an effective radiolytic mechanism simulated by external radiation.