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RuSn6[(Al1/3–xSi3x/4)O4]2wird bei Festkörperreaktionen von RuO2, SnO2, Sn und Si im Korundtiegel bei 1273 bis 1373 K erhalten. Die Verbindung kristallisiert kubisch in der Raumgruppe Fm 3 m (a = 9.941(1) Å, Z = 4, R1= 0.0277, wR2= 0.0619), ist halbleitend und an der Luft stabil. Mößbaueruntersuchungen und Bindungslänge–Bindungsstärke‐Betrachtungen rechtfertigen eine ionische Grenzformulierung Ru2+Sn62+[(Al1/3–x3+Si3x/44+)O42–]2. Zentrales Strukturmotiv der Kristallstruktur sind voneinander isoliert angeordnete RuSn6‐Oktaeder. Diese sind nur über Sauerstoffatome, die tetraedrisch über den Flächen der Oktaeder angeordnet und partiell mit Al bzw. Si besetzt sind, miteinander verbunden. Damit stellt diese Verbindung eine Variante des Pentlandit‐Strukturtyps dar.

¹¹⁹Sn and ⁹⁹Ru Mössbauer spectroscopy was used to investigate catalysts of ruthenium and tin supported on activated carbon (Ru−Sn/C) containing 2 wt % ruthenium and having Sn:(Sn+Ru) ratios between zero and 0.4. Samples were subjected to different reducing and oxidizing treatments, and suitable precursor products were studied. Four major components in the ¹¹⁹Sn Mössbauer spectra are attributed to oxidic Sn(II) and Sn(IV) and to Ru−Sn and Ru−Sn−Ox species forming on the surface of ruthenium metal particles. In addition to this, the ¹¹⁹Sn spectra reveal the presence of minor amounts of Ru3Sn7. While some of the features of the ⁹⁹Ru Mössbauer spectra cannot be interpreted unambiguously, the presence of tin leads to a substantial increase of the Lamb−Mössbauer factor of the metallic ruthenium particles, which shows that tin strengthens the attachment of the particles to the support even at very low tin loadings. None of the ruthenium−tin phases on the catalysts can be clearly identified as those responsible for the development of the catalytic activity and selectivity. The observed close contact between the two metals, however, appears to be decisive for the formation of catalytically active sites during the induction period at the beginning of the reaction.

A Mössbauer measurement of the E2/M1 mixing ratio of the 77 KeV transition in197Au yielded d=-0.352±0.005. With this result, Mössbauer absorption spectra of KAu(CN)2 single crystals show that the electric field gradient at197Au in this compound is negative. This implies that the field gradient is mainly produced by 6pz electrons. The data also indicate a large vibrational anisotropy of Au in KAu(CN)2.

The contributions made by Ir Mössbauer spectroscopy to the determination of nuclear parameters, as well as applications in solid state physics and chemistry, are reviewed. In addition, a brief description of experimental techniques and source preparation procedures is given.

We have measured119Sn Mössbauer spectra of the CePtSn and (Ce0.9La0.1)NiSn compounds in the range from 1.5 to 293 K. In CePtSn, the spectra observed above 8 K are well explained by an electric quadrupole interaction. The spectral shape changes below 8 K due to the presence of a magnetic hyperfine field produced by the ordering of the Ce magnetic moments. We have analyzed these spectra assuming an incommensurate magnetic structure. The temperature dependence of the magnetic hyperfine field matches with anS=1/2 mean field curve with a step at 5 K. In (Ce0.9La0.1)NiSn, no magnetic order exists down to 1.5 K.

A high temperature superconductor with the composition YBa2Cu2.9Au0.1O7−δ was studied by Mössbauer spectroscopy with the 77 keV gamma rays of197Au, by X-ray diffraction, and by magnetization measurements. The main component in the Mössbauer spectrum, a quadrupole doublet with an isomer shift of +3.29 mm/s with respect to metallic gold and a quadrupole splitting of 3.61 mm/s, can be attributed to Au3+ in a square planar oxygen coordination, as is expected for gold replacing Cu(1). A further, weak doublet becomes dominant upon reduction of the specimen, and has an isomer shift of +3.46 mm/s and a quadrupole splitting of 7.12 mm/s. This component may be Au+ or Au3+ in an unusual coordination. Only a small fraction of the gold was found to be metallic in both the oxidized and the reduced state.

The anomalous temperature dependence ot the f-factor arising from the diffusion of interstitials has been studied for57Fe in hydrides and deuterides of vanadium and niobium at temperatures between 6 and 500K. Isotope effects in both the diffusion rate of the interstitials and the magnitude of the displacements of the probes are observed. The centre shift and quadrupole splitting of the patterns provide further information on the hydrogen distribution near the probes and on phase transition temperatures.

From Mössbauer spectra of the 36.2keV and 69.5keV gamma rays of189Os, isomer shifts and electric quadrupole interactions for a number of chemical compounds of osmium in the oxidation states +8, +6, +4, +3, and +2 were obtained. The results show that the dependence of the isomer shifts on the oxidation state of Os follows the general pattern established for other transition elements like Ru and Ir. A comparison of the isomer shift data with electron densities at the Os nuclei resulting from relativistic self-consistentfield calculations for free Os ions yields? 2> [36 keV]=-2.0 · 10-3 fm2 and? 2> [69 keV]=-0.13 · 10-3 fm3 for the changes of the mean-square nuclear charge radius of189Os. These values are in qualitative agreement with an interpretation of the low-energy level scheme of189Os in terms of two rotational bands.

We have measured the Mössbauer spectrum of the adduct of chloro(carbonyl)bis(triphenylphosphine)iridium (CCTI) with buckminsterfullerene (C60) and, for comparison, the spectra of both the parent compound CCTI and its adduct with tetracyanoethylene, (CCTI-TCNE) [1].In another series of experiments di-μ-chloro-bis(1,5-cyclooctadiene)-diiridium, Ir2C12(COD)2 and its adduct with C60 were studied [2].The Mössbauer spectra were interpreted based on the σ donating and π accepting properties of the ligands (including C60) around Iridium.

35Cl and 75As NQR spectra have been recorded for six gold(I) chloride complexes with phosphine, arsine and sulfide ligands. Though no 197Au–NQR signals were detected, good 197Au-Mössbauer spectra could be obtained for the same compounds and some homologs. A discussion of the results has shown, that no consistent correlation is evident between the nature of the ligands and the 35Cl and 75As quadrupole coupling constants, 197Au isomeric shifts and quadrupole splittings.

197Au Mössbauer spectra have been recorded for a series of di- and trinuclear complexes of gold in different oxidation states and coordination numbers. While the interpretation of isomer shift and quadrupole coupling data is straightforward at least for groups of closely related compounds, the correlation of the line intensities with the molecular structure is more problematic. The results show that the relative line intensities in the spectra are largely determined by intramolecular motions. The recoil-free fractions may differ so much that stoichiometry-related structure assignments become hazardous.

Lattice defects in NbMo57Co alloys produced by neutron irradiation at 4.6 K and by cold working were investigated by Mössbauer spectroscopy. On isochronal annealing up to about 100 K, trapping of two different types of mobile interstitials at the57Co probe atoms was observed as additional lines in the spectra. These are characterized by centre shifts of +0.44 mm/s and +0.41 mm/s relative to57Co on substitutional lattice sites and by large quadrupole splittings of 1.50 mm/s. Above 640 K, vacancy trapping was observed. With the onset of recrystallization, dislocation pinning was found in both the neutron irradiated and the cold worked sample.

Chelato‐dicarbonyl‐iridium(I) compounds of the composition Ir(CO)2LL or Ir(CO)2LCl, where LL stands for a singly‐charged bidendate organic ligand and L for a monodendate, neutral organic base, have been studied by Mo¨ssbauer experiments with the 73 keV gamma rays of 193Ir. The results indicate that for these compounds the formation of columnar stacks with metal–metal bonds goes along with a reduction of both the magnitude of the electric quadrupole interaction and the electronic charge density at the Ir nuclei. A qualitative explanation for these results is attempted.

Mössbauer spectra of a synthetic, pure almandine (Alm100) and a natural almandine-rich garnet (Alm86) were taken at temperatures between 295 and 4.2 K.

Hydrides of Ni0.70Cu0.30prepared both electrolytically and under high pressures of hydrogen gas were studied by Mössbauer spectroscopy on dilute57Fe probes and by magnetization measurements. At hydrogen-to-metal ratios abovex≈0.3 no ferromagnetism is observed down to 4.2 K. The dependence of the mean change of the isomer shift on the hydrogen content of the samples reveals a repulsive interaction between the hydrogen interstitials and the iron probes. The effect of this interaction is, however, less pronounced than for57Fe in the hydrides of pure nickel. This difference can be attributed to a competition of the repulsive Fe−H and Cu−H interactions.

Acetylene hydrochlorination catalysts consisting of activated carbon impregnated with a solution of HAuCl4·xH2O in aqua regia have been studied by197Au Mössbauer spectroscopy. The relative amounts of AuCl4−, of Au(0), and of an Au(J) species formed under certain process conditions were determined quantitatively. Deactivation of the catalyst at low and high temperatures was shown to be due to different mechanisms, and the reactivation of the catalyst by Cl2gas was studied.

The gold species present on activated carbon after adsorption from solutions of Au(CN)2−have been studied by197Au Mössbauer spectroscopy as a function of the pH value of the solution, the loading of the carbon, the coadsorption of polyvalent cations, and the treatment of the samples after adsorption. The gold was found to be adsorbed mainly as Au(CN)2−. Coadsorbed polyvalent cations (Ca²+, Gd³+) have no influence on the Mössbauer parameters of the adsorbed gold complex. After adsorption from acidic solutions (pH ≲ 4), one finds a substantial amount of adsorbed gold with Mössbauer parameters similar to those of crystalline AuCN. Presumably, this gold is bound in Aux(CN)x+1oligomers which form during drying. An additional product with Mössbauer parameters close to those of KAu(CN)2Cl2was observed on dried samples after adsorption at pH 1. A minor gold species with an uncommonly small electric quadrupole splitting was found on wet carbons but disappeared on drying.

The Ir-Fe and Ir-Ni alloy systems were studied over the whole composition range by means of the nuclear resonance absorption of the 73 keV y-rays of 193Jr and of the 14.4 keV y-rays of 57Fe. The magnetic hyperfine field at the Ir-nuclei in Ir-Ni alloys decreases approximately linearly with the Ir concentration from - 460 kOe at 4.2 K in very dilute alloys to zero at about 20 at.-% Ir. This behaviour is paralleled by the decrease of the magnetic moment per Ni atom as determined from bulk magnetization measurements. The hyperfine fields at both Ir and Fe were measured for the ferromagnetic bcc phase of the Ir-Fe system. They turned out to be virtually independent of concentration with values of about -1400 kOe and - 330 kOe, respectively. Linewidths increasing with the Ir concentration indicate a distribution of hyperfine fields. The fee phase of the Ir-Fe system has been found to be paramagnetic at 4.2 K throughout the range of its existence. The dependence of the hyperfine fields on concentration is discussed in terms of a rigid 3d-band model combined with local shielding. A discussion of the concentration dependence of the 193Ir and 57Fe isomer shifts has to take into account lattice expansion as well as band repopulation effects.

Zusammenfassung Mit Hilfe des Mößbauer-Effektes wurde Kernresonanzabsorption im 84 keV-Niveau von Yb170 nachgewiesen. Durch Messung der Resonanzabsorption als Funktion der Doppler-Verschiebung zwischen einer Tm170-Metallquelle und einem Yb2O3-Absorber bei 20° K wurde eine Hyperfeinstrukturaufspaltung des 84 keV-Niveaus beobachtet. Aus einer aufgelösten Resonanzlinie ergibt sich die Halbwertszeit des 84 keV-Niveaus zu (1,5±0,2)·10−9 sec. Die Aufspaltung kann durch eine Quadrupolwechselwirkung im Yb2O3 erklärt werden.