Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds

Hauser, Andreas; Jeftić, Jelena; Romstedt, Harald; Hinek, Roland; Spiering, H.

doi:10.1016/s0010-8545(99)00111-3

Cited by 301 publications

(264 citation statements)

References 36 publications

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“…[21] The nature of the intermediate phase formed in the plateau has been revealed in a recent detailed structural study performed over a wide range of temperatures. [22] In contrast to previous studies, [23] this new structural analysis clearly establishes that long-range order occurs defining infinite -[LS-HS-LS]-chains of [Fe(2-pic) 3 ] 2 + molecules in the plateau. Within each chain, the molecules interact with each other strongly via hydrogen bonding through Cl À anions and EtOH solvent molecules.…”

Section: Resultscontrasting

confidence: 80%

“…The corresponding calculated relaxation curves are included in Figure 10. In mean-field approximation and in the thermally activated region the acceleration factor a % G/k B T. [23] Thus, as expected, a 11 and a 22 both decrease with increasing temperature and a 11 is somewhat smaller than a 22 . However, the absolute values of the acceleration parameters are substantially smaller than G/ k B T. There are several reasons for this: a) 40 to 50 K is not fully in the thermally activated region, b) there is a comparatively large inhomogeneous distribution of the zero-point energy difference and c) the specific nearest neighbor interactions of the "antiferromagnetic" type influence the relaxation behavior.…”

Section: Differential Scanning Calorimetry (Dsc) Measurementssupporting

confidence: 60%

“…Both steps show the typical sigmoidal self-accelerated shape due to the cooperative effects. [23] The experimental curves at these elevated temperatures actually start at a total HS fraction of 85-90 %, because Fe(5) decays on a much faster time scale at higher temperatures. Following the spirit of the treatment of the thermal spin transition and ignoring the finer details, the iron centers can again be grouped into two sets.…”

Section: Differential Scanning Calorimetry (Dsc) Measurementsmentioning

confidence: 93%

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Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

Niel

Thompson

Goeta

et al. 2005

Chemistry A European J

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129

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The compound {Fe(pmd)[Ag(CN)2][Ag2(CN)3]} (pmd=pyrimidine) was synthesized and characterized. Magnetic, calorimetric and single crystal visible spectroscopic studies demonstrate the occurrence of a two-step high-spin (HS) low-spin (LS) transition. The critical temperatures are Tc1=185 and Tc2=148 K. Each step involves 50 % of the iron centers, with the low-temperature step showing a hysteresis of 2.5 K. The enthalpy and entropy variations associated with the two steps are H1=3.6±0.4 kJ mol-1 and S1=19.5±3 J K-1 mol-1; H2=4.8±0.4 kJ mol-1 and S2=33.5±3 J K-1 mol-1. Photomagnetic and visible spectroscopy experiments show that below 50 K, where the LS state is the thermodynamically stable state, the compound can be switched quantitatively to the HS state using green-red light (550-650 nm). HS-to-LS relaxation experiments in the dark at temperatures between 15 and 55 K show that the relaxation takes place via a two-step cooperative process, which was analyzed in the context of the mean field theory. The crystal structure has been studied at 290, 220, 170, 90 and 30 K together with 30 K after irradiation. The compound adopts monoclinic symmetry (P21/c, Z=16) at all temperatures. There are five [FeN6] pseudo-octahedral sites linked by pmd, [Ag(CN)2]- and [Ag2(CN)3]- bridging ligands to form an unprecedented three-dimensional (6,6) topology. The structural analysis allows for an understanding of the microscopic mechanism of the two-step behavior of the thermally induced spin transition as well as the corresponding relaxation of the photoexcited compound based on the individual changes of the five sites. Synergy between metallophilic interactions and the spin transition is also shown by the variation of the AgAg distances. Correlations between the variation of the unit-cell volume and the change of AgAg interactions within each step with the asymmetric change of the anomalous heat capacity have also been inferred

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Section: Resultscontrasting

confidence: 80%

Section: Differential Scanning Calorimetry (Dsc) Measurementssupporting

confidence: 60%

Section: Differential Scanning Calorimetry (Dsc) Measurementsmentioning

confidence: 93%

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Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

Niel

Thompson

Goeta

et al. 2005

Chemistry A European J

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129

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“…5 König and Madeja's papers were not the first statement of the spin-crossover effect. While the idea had been discussed previously, 6 the first rigorous treatment had come in 1964 from 70 Ewald, Martin et al 7 That study had used spin-crossover to explain temperature-dependent magnetic moments in a series of iron(III) complexes dating from the 1930s.…”

mentioning

confidence: 99%

“…Moreover, it also inhibits relaxation of the material below T LIESST by quantum mechanical tunnelling. 5 Interest in the spin-crossover phenomenon greatly increased in the 1990s. This was inspired by Kahn et al, who realised that spin-transition compounds with thermal hysteresis exhibit 90 magnetic and colorimetric bistability, which could be harnessed in display or memory devices.…”

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The foundation of modern spin-crossover

Halcrow

2013

Chem. Commun.

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Iron: Inorganic & Coordination ChemistryBased in part on the article Iron: Inorganic & Coordination Chemistry by Pelham N. Hawker & Martyn V. Twigg which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

Burgess

Twigg

2005

Encyclopedia of Inorganic Chemistry

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Iron, the most abundant transition element in the biosphere, is essential in higher forms of life and its compounds have numerous industrial applications. The element has catalytic properties. Several simple iron compounds are industrially important, for example, large amounts of iron oxides are produced for pigment and magnetic recording media applications. Oxidation states ranging from −2 to +6 are known, the most familiar are +2 (ferrous iron) and +3 (ferric iron). Most common complexes are octahedral, although examples of higher (e.g. seven coordinate) and lower (e.g. tetrahedral and square planar) geometries are well known, as are a variety of mixed oxidation state compounds. Depending on ligands involved high‐ and low‐spin complexes can be formed, and temperature‐dependent spin‐state crossover complexes are well documented. The thermodynamics and kinetics of reactions of low‐spin iron(II) complexes with ligands such as 1,4‐diimines and CN − have been extensively studied. While low‐spin iron(II) is present in biological systems such as oxygenated heme centered oxygen carriers and thiolate clusters, iron(III) is more common. Thiolate‐containing iron clusters form readily, and here mixed oxidation states are a prominent feature that is exploited in some important electron transfer proteins. Microorganism iron uptake is facilitated by tris‐catecholate and tris‐hydroxamate ligands like enterobactin that have an extraordinarily high affinity for iron(III) that results in a dramatic enhancement of the 3+ relative to the 2+ state in terms of redox potential.

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Cooperative phenomena and light-induced bistability in iron(II) spin-crossover compounds

Cited by 301 publications

References 36 publications

Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

Thermal‐ and Photoinduced Spin‐State Switching in an Unprecedented Three‐Dimensional Bimetallic Coordination Polymer

The foundation of modern spin-crossover

Iron: Inorganic & Coordination ChemistryBased in part on the article Iron: Inorganic & Coordination Chemistry by Pelham N. Hawker & Martyn V. Twigg which appeared in theEncyclopedia of Inorganic Chemistry, First Edition.

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