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  • 1
    Electronic Resource
    Electronic Resource
    High-spin .fwdarw. low-spin relaxation kinetics and cooperative effects in the hexakis(1-propyltetrazole)iron bis(tetrafluoroborate) and [Zn1-xFex(ptz)6](BF4)2(ptz = 1-propyltetrazole) spin-crossover systems (1986)
    s.l. : American Chemical Society
    Inorganic chemistry 25 (1986), S. 4245-4248 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00243a036
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray structure study of the light-induced metastable states of the spin-crossover compound [Fe(mtz)6](BF4)2 (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 229-238 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Iron(II) complexes exhibiting thermal spin-crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST) and from the LS to the HS state by irradiation with red light (reverse LIESST). The lifetime of the metastable LIESST states may be sufficiently long to enable an X-ray diffraction study. The lattice parameters of a single crystal of [Fe(mtz)6](BF4)2 (mtz = methyltetrazole) (space group P21/n) were measured between 300 and 10 K. While one Fe lattice site (A) of the crystal changes from the HS to the LS state near 78 K, the other site (B) remains in the LS state. Using the green light (514 nm) of an argon ion laser the crystal was quantitatively converted to the HS state at 10 K. Irradiation of the crystal at 10 K by red light of a laser diode (820 nm) with site A in the LS and site B in the HS state converts site B almost completely to the LS state. The lattice parameters of both metastable states were measured up to 50 K, where they start to decay on a minute timescale. At 10 K, a full data set for evaluation of the crystal structure was recorded. The volume change of the crystal per complex molecule accompanying the spin transition is 31.5 Å3 at site A and close to zero [−0.21 (14) Å3] at site B.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889801000462
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray study of the light-induced metastable state of a spin-crossover compound (2000)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 201-205 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Iron(II) complexes exhibiting thermal spin crossover may be converted from the 1A1 low-spin (LS) state to the 5T2 high-spin (HS) state by irradiation with green light (light-induced excited spin-state trapping, LIESST). The lifetime of the metastable LIESST state may be sufficiently long for X-ray diffraction study. The lattice parameters of a single crystal of [Fe(ptz)6](BF4)2 (ptz = propyltetrazole) were measured between 300 and 10 K, while the crystal changed from the HS to the LS state near 135 K. Using the green light (514 nm) of an argon-ion laser, the crystal was quantitatively converted to the metastable LIESST state at 10 K; its lattice parameters were measured up to 50 K, at which point the LIESST state begins to decay on a minute timescale. The change of the lattice parameters can be interpreted by a superposition of a normal temperature dependence, for which the isostructural zinc compound served as a reference, and an almost temperature-independent part which is proportional to the fraction of molecules in the HS state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889899014739
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  • 4
    Electronic Resource
    Electronic Resource
    Light-induced excited spin-state trapping of the Fe(ppi)2(NCS)2 complex (1996)
    Springer
    Transition metal chemistry 21 (1996), S. 472-473 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00140795
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  • 5
    Electronic Resource
    Electronic Resource
    The [Fe(etz)6](BF4)2 Spin-Crossover System - Part One: High-Spin ⇌ Low-Spin Transition in Two Lattice SitesDedicated to Professor Hans Georg von Schnering on the occasion of his 65th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1427-1434 
    Details
    ISSN: 0947-6539
    Keywords: iron complexes ; LIESST ; spin crossover ; tetrazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [Fe(etz),](BF,), spin-cross-over system (etz = 1-ethyl-1 H-tetrazole) crystallizes in space group P1, with the following lattice constants at 298 K: a 10.419(3), b=15.709(1), c = 18.890(2) Å = α = 71.223(9), β =77.986(10), and γ = 84.62(1)° V = 2862.0(9) Å3 and Z = 3. Two nonequivalent lattice sites, one without (site A) and one with (site B) inversion symmetry, are observed. The population of the two sites nA:nB is 2:l. Iron(II) on site A undergoes a thermal low-spin (LS) → high-spin (HS) transition with T1/2I, = 105 K. whereas that on site B remains in the high-spin state down to cryogenic temperatures. Application of external pressure of up to 1200 bar between 200 and 60 K does not cause formation of the low-spin state on site B. On site A the high-spin state can be populated as a metastable state at 20 K by irradiating the sample with λ = 514.5 nm; on site B a light-induced population of the low-spin state can be achieved with λ = 820 nm.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021115
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  • 6
    Electronic Resource
    Electronic Resource
    The [Fe(etz)6](BF4)2 Spin-Crossover System - Part Two: Hysteresis in the LIESST RegimeDedicated to Professor Karl Heinrich Lieser on the occasion of his 75th birthday (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 1435-1439 
    Details
    ISSN: 0947-6539
    Keywords: hysteresis ; iron complexes ; LIESST ; spin crossover ; tetrazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the [Fe(etz)6](BF4)2 spincrossover system the iron(II) complexes occupy two nonequivalent lattice sites, sites A and B. Complexes on site A show a thermal high-spin (HS) → low-spin (LS) transition at 105 K, whereas complexes on site B remain in the HS state down to 10 K. Complexes on both sites exhibit light-induced spin state conversions (LIESST) at 20 K: LS → HS on site A with λ = 514.5 nm, and HS → LS on site B with λ = 820 nm. The relaxation processes subsequent to the HS ⇌ LS conversion on site B reveal a light-induced HS⇌LS bistability for the complexes on site B at 70 K. The bistability as well as the absence of a thermal spin transition on site B are attributed to a thermal hysteresis for the B-site complexes with a critical temperature T↑c≍77 K on heating. This hysteresis can be interpreted in terms of strong cooperative effects of elastic origin, which, in addition, cause characteristic deviations of the relaxation on site B from first-order kinetics (self-acceleration). In contrast, the HS → LS relaxation at 60 K on site A after irradiation with λ = 514.5 nm shows an unusual self-retardation.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960021116
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  • 7
    Electronic Resource
    Electronic Resource
    Intersystem crossing in Fe(II) coordination compounds (1994)
    Springer
    Hyperfine interactions 90 (1994), S. 77-87 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fe(II) spin-crossover systems can be quantitatively converted from the low-spin (LS) to the high-spin (HS) state well below the thermal transition temperature by irradiating either into the metal-ligand charge transfer or d-d absorption bands, and even in low-spin systems a transient population of the HS state can be achieved. This fact can be made use of to determine HS → LS relaxation rate constants for a wide variety of Fe(II) spin-crossover and low-spin systems. The HS → LS relaxation shows strong deviations from an Arrhenius behaviour, with nearly temperature-independent tunnelling below ∼70 K and a thermally activated process above ∼100 K. The range of more than 12 orders of magnitude in the low temperature tunnelling rate constant can be understood in terms of a non-adiabatic multiphonon process, where in the strong vibronic coupling limit an inverse energy gap law holds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02069119
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  • 8
    Electronic Resource
    Electronic Resource
    Evaluation of single crystal57Fe Mössbauer spectra of finite thickness by the intensity matrix method: FeCl2·4H2O (1977)
    Springer
    Hyperfine interactions 3 (1977), S. 221-229 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The calculation of the absorption cross section for a polarized single crystal absorber of finite thickness is described using an intensity matrix method. The method is applied to the dipole transition of the quadrupole split Mössbauer spectrum of FeCl2·4H2O. For thickness corrections a simple hyperbola function is stated which approximates the absorption area of thick absorbers of an effective thickness from 0.4–10 within less than 1 per cent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01021552
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  • 9
    Electronic Resource
    Electronic Resource
    Dynamics of spin state conversion processes in the solid state (1989)
    Springer
    Hyperfine interactions 47-48 (1989), S. 343-356 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High spin (HS) ⇌ low spin (LS) conversions in transition metal complexes are nonradiative transitions between spin states. In this contribution, we present a study of the temperature and pressure dependence of the HS ⇌ LS intersystem crossing dynamics. For some iron(II) spin-crossover complexes, the rate constants were determined by line shape analysis of57Fe Mössbauer spectra. Their temperature dependence is described by an Arrhenius equation, their pressure dependence is interpreted within absolute rate theory. HS → LS conversion rates at low temperatures were determined from the relaxation of light-induced formation of HS states, monitored by optical spectroscopy. Deviations from a simple Arrhenius behaviour due to cooperative effects were found for one complex, low temperature tunnelling is observed for another.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02351617
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  • 10
    Electronic Resource
    Electronic Resource
    Thermisch und optisch schaltbare Eisen(II)-KomplexeProfessor Heinrich Nöth zum 65. Geburtstag gewidmet (1994)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 106 (1994), S. 2109-2141 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In der Übergangsmetallchemie gibt es eine Klasse von Komplexverbindungen, bei denen eine Temperaturerniedrigung einen Wechsel im Spinzustand des Zentralatoms vom High-Spin- in den Low-Spin-Zustand bewirkt. Dabei ändern sich die magnetischen und optischen Eigenschaften, über die der thermische Spinübergang (auch Spincrossover genannt) sehr gut verfolgt werden kann. Dieses Phänomen tritt sowohl in flüssiger Phase als auch im Festkörper auf. Eine herausragende Stellung nehmen Eisen(II)  -  Spincrossover  -  Verbindungen ein, in denen der Spinübergang im Festkörper auf sehr unterschiedliche Weise  -  graduell, abrupt, mit Hysterese oder stufenweise  -  verlaufen kann und mit Mößbauer- und optischer Spektroskopie, mit magnetischen Suszeptibilitäts- und Wärmekapazitätsmessungen sowie durch Kristallstrukturanalyse intensiv untersucht worden ist. Die kooperative Wechselwirkung zwischen den einzelnen Komplexmolekülen kann befriedigend durch elastische Eigenschaften und durch die Änderung von Gestalt und Volumen der Komplexmoleküle beim Spinübergang erklärt werden. Bei Untersuchungen an Eisen(II)-Spincrossover-Verbindungen konnte man beobachten, daß sich der Low-Spin-Zustand mit grünem Licht in den High-Spin-Zustand umschalten läßt, der bei tiefen Temperaturen eine nahezu unendlich lange Lebensdauer haben kann (LIESST = Light-Induced Excited Spin State Trapping). Mit rotem Licht läßt sich der metastabile High-Spin- wieder in den Low-Spin-Zustand zurückschalten. Der Mechanismus des LIESST-Effekts ist aufgeklärt, die Zerfallskinetik im Detail untersucht und im Rahmen der Theorie strahlungsloser Übergänge verstanden. Anwendungen des LIESST-Effekts in der optischen Informationstechnik sind denkbar.
    Additional Material: 36 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19941062006
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