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  • 1
    Electronic Resource
    Electronic Resource
    Application of61Ni Mössbauer spectroscopy to chemical problems (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 231-235 
    Details
    ISSN: 0392-6737
    Keywords: Mössbauer spectra ; Structure, bonding, conformation, configuration and isomerism of biomolecules ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Using the possibility to produce61Co sources at the MAinz MIcrotron,61Ni Mössbauer spectroscopy was applied to different kinds of chemical problems. Measurements of isomer shifts andV zz values in some common compounds and compounds with unusual chemical bonding for comparison with band structure calculations, measurement of61Ni Mössbauer parameters in model compounds for hydrogenase and dehydrogenase with an active [NiS4] centre, and study of novel binary NiF3 compounds at helium temperature are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458896
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  • 2
    Electronic Resource
    Electronic Resource
    Fascinating electronic games in iron complexes (1996)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 18 (1996), S. 107-136 
    Details
    ISSN: 0392-6737
    Keywords: Crystal and ligand fields ; Mossbauer effect ; other γ-ray spectroscopy ; Visible and ultraviolet spectra ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary Coordination compounds of transition metal ions with open-shell electron configurations may exhibit dynamic electronic-structure phenomena, depending on the nature of the coordinating ligand sphere. The change of spin state with temperature («thermal spin-crossover»), light-induced electron transfer processes leading to long-lived metastable charge and spin states (e.g., «LIESST» effect), are some of the fascinating electronic games encountered in transition metal compounds, which are presently under extensive study by chemists and physicists. Mössbauer spectroscopy plays a dominant role in the investigation of such phenomena in iron compounds, as will be demonstrated in this paper. This work will focus on selected examples of «thermal spin-crossover» in iron(II) complexes and switching between different spin states by irradiation with light of different wavelength (LIESST effect), demonstrating that Mössbauer spectroscopy besides other physical techniques proves to be a highly elegant tool for following the spin state conversion and the concomitant changes of molecular and crystal structure properties. Finally, Mössbauer emission spectroscopy, both time integral and time differential, has been employed to generate and identify long-lived excited spin states by making use of the nuclear disintegration of57Co as an intrinsic molecular light source (NIESST=nuclear decay-induced excited-spin-state trapping). Lifetime measurements by optical techniques on LIESST states and by time-differential Mössbauer coincidence spectroscopy on NIESST states prove that the relaxation pathways in the mechanisms for LIESST and NIESST are identical.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02458887
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  • 3
    Electronic Resource
    Electronic Resource
    Investigation of ultrathin iron and iron/nickel layers prepared from Langmuir-Blodgett films (1996)
    Springer
    Applied physics 62 (1996), S. 317-322 
    Details
    ISSN: 1432-0630
    Keywords: 68.65 ; 76.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Oxidic and metallic iron and iron/nickel multilayers, formed after thermal and chemical treatment of Langmuir-Blodgett films, were investigated. Reduced iron-stearate multilayers were compared with evaporated films concerning their phase composition and their lateral homogeneity. The sequence of metallic and oxidic iron in the films after reduction was determined. Oxidic iron/nickel mixed layers can be prepared from Langmuir-Blodgett films, in which a magnetically non-ordered Fe3+ phase exhibiting a distribution of the quadrupole splitting is observed. After reduction of such layers, two metallic iron phases appear dependent on the nickel concentration. The hyperfine field distribution of the magnetically ordered metallic phase can be evaluated using a method proposed by Rancourt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01594229
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of ultrathin iron and iron/nickel layers prepared from Langmuir-Blodgett films (1996)
    Springer
    Applied physics 62 (1996), S. 317-322 
    Details
    ISSN: 1432-0630
    Keywords: PACS: 68.65; 76.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Oxidic and metallic iron and iron/nickel multilayers, formed after thermal and chemical treatment of Langmuir-Blodgett films, were investigated. Reduced iron-stearate multilayers were compared with evaporated films concerning their phase composition and their lateral homogeneity. The sequence of metallic and oxidic iron in the films after reduction was determined. Oxidic iron/nickel mixed layers can be prepared from Langmuir-Blodgett films, in which a magnetically non-ordered Fe3+ phase exhibiting a distribution of the quadrupole splitting is observed. After reduction of such layers, two metallic iron phases appear dependent on the nickel concentration. The hyperfine field distribution of the magnetically ordered metallic phase can be evaluated using a method proposed by Rancourt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01594229
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal and light-induced spin transition in [Fe(bpen)X2] (bpen = 1,6-Bis(2-pyridyl)-2,5-diazahexane, X = NCS-, NCSe-)Dedicated to Professor Max Herberhold on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1129-1133 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; kinetics ; magnetic susceptibility ; Mössbauer spectroscopy ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal and light-induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mössbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high-spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation of the metastable spin states after rapid cooling is observed at temperatures between 35 and 42.5 K and shows strong deviations from single exponential behavior. The spin-transition behavior changes drastically on substitution of the thiocyanate ions by NCSe-. In [Fe(bpen)(NCSe)2] a gradual and complete spin transition between 140 and 250 K is observed (T1/2 = 181 K). Irradiation of the compound with green light at low temperatures does not result in formation of long-lived metastable HS states. The spintransition curves derived from magnetic susceptibility and Mössbauer studies show good agreement for each compound, and no hints of significantly different Lamb-Mössbauer factors for the HS and LS states are observed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020912
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  • 6
    Electronic Resource
    Electronic Resource
    High-spin → low-spin relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and thermal spin-state trapping - dynamics of spin transition versus dynamics of phase transitionDedicated to Professor Gerhard Herberich on the occasion of his 60th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1134-1138 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; magnetic susceptibility ; Mössbauer spectroscopy ; phasetransitions ; spin crossover ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The iron(II) complex [Fe(bpp)2]-(CF3SO3)2 H2O (bpp = 2,6-bis(pyrazolyl-3-yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≍285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse-LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin-state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin-state trapping is triggered by an additional structural phase transition of the system.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.1460020913
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  • 7
    Electronic Resource
    Electronic Resource
    Lamb–Mössbauer factor of electronically excited molecular states measured by time‐differential Mössbauer emission spectroscopy (1998)
    Springer
    Hyperfine interactions 113 (1998), S. 351-355 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Lamb-Mössbauer Factor (LMF) of molecular crystals is expected to depend on the electronic molecular states by their different intramolecular vibrational frequencies. Revisiting Mössbauer spectra obtained by time differential Mössbauer emission spectroscopy of the low spin compound [57Co/Mn(bipy)3](PF6)2 (bipy= 2,2'-bipyridine) a ratio of 1.25 for the LMFs of the low spin ground state and of an excited high spin state decaying in the Mössbauer time window could be evaluated. The difference found is in line with the change of LMF observed for spin crossover compounds where the excited high spin state is populated by the so‐called LIESST effect. The initial population of the high spin state is close to 100%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012644220872
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  • 8
    Electronic Resource
    Electronic Resource
    Aftereffects in zeolite‐encapsulated 57Co‐complexes (1998)
    Springer
    Hyperfine interactions 113 (1998), S. 331-339 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Tris(2,2'-bipyridyl)-57CoII and bis(2,2':6',2'-terpyridine)-57CoII complexes were synthesised in the supercages of zeolite‐Y in order to study the effect of molecular isolation on the aftereffects of the 57Co(EC)57Fe decay. As compared to the regular crystalline salts of the complex ions where, according to the emission Mössbauer spectra, the most abundant species is low‐spin FeII, the molecular isolation in the zeolite resulted in a larger fraction of low‐spin FeIII and a varying amount of high‐spin Fe2+ species. In the investigated temperature range, 20 K to 295 K, the majority of the changes was observed above 80 K. In the case of tris (2,2'-bipyridyl)-57CoII-Y, the most characteristic change occurred in valence states, while for bis (2,2':6',2'-terpyridine)-57CoII‐Y, the temperature dependence of the spin states was more prominent. The change in the low spin valence states is explained partly by donor-acceptor properties of the zeolite lattice. The variation in the high spin fraction is explained by radiation damage of the ligand sphere and/or fragmentation of the complex ion followed by incomplete recombination in the supercage. Molecular isolation itself did not seem to increase the chance of fragmentation (as a consequence of charge neutralization following Auger ionization) of these highly conjugated complex molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1012640119963
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  • 9
    Electronic Resource
    Electronic Resource
    The debye-waller factor in spincrossover molecular crystals: a mössbauer study on [FexZn1−x(ptz)6](BF4)2 (1995)
    Springer
    Hyperfine interactions 95 (1995), S. 107-128 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In a first approximation the Debye-Waller factor (DWF) of molecular crystals is factorized into a molecular and a lattice part:f=f m f l. In the case of spincrossover compounds there is the unique possibility to measure differences of both parts in the two spin states by switching the spin states with the LIESST effect. Measurements of the DWF depending on temperature, γ-ray direction and spin state were performed with57Fe-Mössbauer spectroscopy on three single crystals (R¯3) of the spincrossover system [FexZn1−x(ptz)6](BF4)2 (ptz=1-propyltetrazole), a concentrated sample withx=1 and diluted ones withx=0.30 andx=0.005. The DWF decreases from 10 to 300 K by a factor of ∼ 100 and its anisotropyf ⊥/f ∥ increases from ∼ 1 to 5.4. The differences of the DWF in the low spin and the high spin state (after LIESST) for the diluted and the concentrated samples were measured at low temperatures (≤ 50 K). From these data both the Grüneisen constant of the lattice γG=2.9 and the lowest IR active intramolecular frequency (45 cm−1 (HS), 58 cm−1 (LS)) have been determined. The contribution of the DWF from the acoustic modes of the lattice is calculated from the elastic constants of rhombohedral [Fe x Zn1−x (ptz)6](BF4)2. The contribution of the optical lattice vibrations is estimated. The influence of different DWF in the two spin states on the evaluation of the fraction of molecules in either spin state from Mössbauer area data is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02146309
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  • 10
    Electronic Resource
    Electronic Resource
    Dynamics of BF 4 - anion reorientation in the spin-crossover compound [Fe(1-n-propyl-1H-tetrazole) 6 ](BF 4 ) 2 and in its Zn II analogue (1999)
    Springer
    The European physical journal 7 (1999), S. 567-571 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 33.15.Vb Correlation times in molecular dynamics - 33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics) - 33.25.+k Nuclear resonance and relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: 19 F and 11 B spin-lattice relaxation times were measured in [ Zn ( ptz ) 6 ] ( BF 4 ) 2 and in the spin-crossover compound [ Fe ( ptz ) 6 ] ( BF 4 ) 2 . For both compounds BF 4 - anion reorientation is active above 50 K. For [ Zn ( ptz ) 6 ] ( BF 4 ) 2 , the anion-reorientation dynamics is different in the temperature regions of 50-90 K, 90-120 K, and above 150 K; between 120 and 150 K it changes rapidly reflecting a structural change. In [ Fe ( ptz ) 6 ] ( BF 4 ) 2 the mechanism for the paramagnetic relaxation involving the 19 F nuclei is found to be of the diffusion-limited type according to the theory of Lowe and Tse. The present results prove that the spin-crossover takes place in a dynamic surrounding and not in a static crystal lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530050382
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