Mössbauer Investigation of the Single Crystal and Powder Sample of Barium Nitroprusside Ba[Fe(CN)5NO]⋅3H2O (BNP)

Hyperfine Interactions - Angle-dependent Mössbauer investigation on single crystals of barium nitroprosside (BNP) using a-, b- and c-crystal cuts has been performed. The EFG tensor has been...     

Siderophores as iron storage compounds in the yeastsRhodotorula minuta andUstilago sphaerogena detected by in vivo Mössbauer spectroscopy

In the yeastsRhodotorula minuta andUstilago sphaerogena siderophores represent the main intracellular iron pool. We suggest a ferritin substituting function of these siderophores in addition to their role as iron transport agents. InRhodotorula transport and storage siderophore is the same compound whereas in Ustilago the iron-storage siderophore is ferrichrome. Besides siderophores, merely two iron metabolites can be observed. Other iron-requiring compounds are at least one order of magnitude less abundant in these yeasts. The ferrous metabolite has been detected in many other microbial systems and seems to be of general occurence and importance.     

Recombination studies of photodissociated MbCO by Mössbauer spectroscopy at low temperatures

Rebinding of carbonmonoxide to myoglobin after photodissociation has been studied by Mössbauer spectroscopy at 57.6 K and below for up to 9 days. The time dependence is reproduced by a set of exponentials representing a distribution of activation enthalpies. A shift to smaller values of these activation enthalpies and of the preexponential factor compared to optical studies at higher temperatures has been observed as well as pumping into long-living states.     

Surface effects of metallic iron particles in zeolite NaX

In situ Mössbauer, magnetization, ferromagnetic resonance and small-angle X-ray scattering measurements are used to characterize iron particles in the zeolite NaX, prepared by thermal decomposition of Fe(CO)₅. The examined system shows a bimodal size distribution of superparamagnetic -Fe particles with mean diameters of 1.2+-0.1 nm located inside the supercages and 3.0 ±1.0 nm located in defect sites of the zeolite. An enhancement of the saturation magnetization of the smaller particles by about 30% with respect to the bulk value has been observed. This enhancement is most likely due to surface effects of ultra-small particles in which 90% of the atoms are surface atoms.     

Molecular magnetism of a linear Fe(III)-Mn(II)-Fe(III) complex. Influence of long-range exchange interaction

The magnetic properties of [L-Fe(III)-dmg₃Mn(II)-Fe(III)-L] (ClO₄)₂ have been characterized by magnetic susceptibility, EPR, and Mössbauer studies. L represents 1,4,7-trimethyl-, 1,4,7-triazacyclononane and dmg represents dimethylglyoxime. X-ray diffraction measurements yield that the arrangement of the three metal centers is strictly linear with atomic distancesd _Fe-Mn=0.35 nm andd _Fe-Fe=0.7 nm. Magnetic susceptibility measurements (3–295 K) were analyzed in the framework of the spin-Hamiltonian formalism considering Heisenberg exchange and Zeeman interaction:=J _Fe-Mn(S _Fe1+S _Fe2)S _Mn +J _Fe-Fe(S _Fe1 S _Fe2) +g_B S _total B. The spinsS _Fe1=S _Fe2 =S _Mn=5/2 of the complex are antiferromagnetically coupled, yielding a total spin ofS _total=5/2 with exchange coupling constantsF _Fe-Mn=13.4 cm^–1 andJ _Fe-Fe= 4.5 cm^–1. Magnetically split Mössbauer spectra were recorded at 1.5 K under various applied fields (20 mT, 170 mT, 4T). The spin-Hamiltonian analysis of these spectra yields isotropic magnetic hyperfine coupling withA _total/(g _{N N})=–18.5 T. The corresponding local componentA _Fe is related toA _total via spin-projection:A _total=(6/7)A_Fe. The resultingA _Fe/(g _NN)=–21.6 T is in agreement with standard values of ferric high-spin complexes. Spin-Hamiltonian parameters as obtained from Mössbauer studies and exchange coupling constants as derived from susceptibility measurements are corroborated by temperature-dependent EPR studies.     

Thermische Zersetzung von Pentacarbonyleisen in Zeolithen des Faujasit-Typs

Thermal Decomposition of Pentacarbonyl Iron in Faujasite-Type Zeolites The nature of the iron species resulting from the title reaction has been elucidated by thermogravimetry, X-ray diffraction, electron microscopy, Mössbauer spectrometry, and by normal analytical methods. The thermal decomposition of Fe(CO)₅ adsorbed in Y-type zeolite yields pure α-Fe. In X-type zeolite Fe(CO)₅ is converted into a highly dispersed form of iron, into iron-subcarbonyl, and into high-spin Fe^II, occupying different sites of the lattice. Dealuminized zeolites adsorb Fe(CO)₅ reversibly. The estimated size of the iron(III) oxide particles formed by air oxidation is in accordance with the assumption that Fe(CO)₅ decomposes in Y-type zeolite with iron migrating to the surface of the zeolite crystals, whereas in X-type zeolite the iron remains inside the zeolite cavities.     

Electronic and magnetic structure of the polymeric system di-imidazolato iron(II)

The polymeric system di-imidazolato iron(II) is synthesized from the reaction of either ferrocene or cyclopentadienyl-irondicarbonyl with imidazole. From Mössbauer measurements in the temperature range 4.2 KT448 K we find two different iron sites in the compound, denoted byA andB, respectively with ratio [A]/[B] = 1.79±0.03. From the isomer shift values we conclude that both Fe ^A and Fe ^B are in the ferrous high-spin state. Below 13.95±0.10 K both subspectra are considerably broadened due to magnetic ordering. From the analysis of the magnetic spectra we derive for the main componentV _zz of the electric field gradient tensorV _zz ^A >0 andV _zz ^B <0. Additionally, we investigate the thermal decomposition of the compound by thermogravimetry in the temperature range 20 °CT 750 °C and by Mössbauer spectroscopy in the temperature range 20 °CT505 °C. The decomposition takes place in four steps. The first step between 20 °C and 190 °C is due to the loss of imidazole nonbonded to iron(II). Comparing the amount of iron with that of pure imidazolato iron(II) we find the formula FeIz₂+0.70 (±0.02) IzH, with Iz standing for doubly deprotonated and IzH for deprotonated imidazole. Step 2 (193 °C<T<235 °C) and step 3 (400 °C<T<500 °C) are found from both methods. Step 4 is above 500 °C. Heat treatment and vacuum conditions affect the thermal decomposition products.Isomer shifts ^A and ^B , and temperature dependent quadrupole splittings E _Q ^A and E _Q ^B are explained using a simple ligand field picture for orbital splittings and occupancies of quasi-tetrahedrally (A) and quasi-octahedrally (B) coordinated ferrous high-spin compounds. Using finally the experimental ratio [A]/[B] = 1.79 we derive for the over-all chemical formula (1.79 Fe ^A Iz_4/2+Fe ^B Iz_4/2+2 IzH) _n = (FeIz₂+0.71 Iz) _–n in agreement with the result which we derived from investigating the thermal decomposition of our compound.Supported by Deutsche Forschungsgemeinschaft     

Metastable isonitrosyl structure of the nitroprusside anion confirmed by nuclear inelastic scattering

Nuclear inelastic scattering (NIS) measurements were performed on a guanidium nitroprusside ((CN(3)H(6))(2)[Fe(CN)(5)NO], GNP) monocrystal at 77 K after the sample was illuminated with blue light (450 nm) at 50 K to populate the two metastable states, MS(1) and MS(2), of the nitroprusside anion. A second measurement was performed at 77 K after warming up the illuminated crystal to 250 K where the metastable states decay to the groundstate. The measured spectra were compared with simulated NIS spectra that were calculated by using density functional methods. Comparison of measured and simulated spectra provides strong evidence for the isonitrosyl structure of the metastable MS(1) state proposed by Carducci et al. (Carducci, M. D.; Pressprich, M. R.; Coppens, P. J. Am. Chem. Soc. 1997, 119, 2669-2678).