Spin crossover in iron(II) tris(2-(2-pyridyl)benzimidazole) complex monitored by the variable temperature EXAFS

Boča, Roman; Vrbová, Martina; Werner, Rüdiger; Haase, Wolfgang

doi:10.1016/s0009-2614(00)00902-7

Cited by 16 publications

(10 citation statements)

References 19 publications

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“…The EXAFS technique can directly measure the local radial pair−distance distribution function around Mn atoms in these materials, thereby providing a structural parameter, such as distances, to compare with magnetic susceptibility data associated with the Mn spin state. The EXAFS technique has been widely successful in determining the local structure in Fe-based SCO species, for example, see refs − . Unlike the studies of Fe compounds, special containment procedures are necessary that present a challenge for obtaining useful EXAFS data on the extremely air-sensitive manganocene compounds; see Experimental Section for details.…”

Section: Resultsmentioning

confidence: 99%

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

et al. 2009

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A water-soluble self-assembled supramolecular host molecule catalyzes the hydrolysis of orthoformates in basic solution. Comparison of the rate constants of the catalyzed and uncatalyzed reactions for hydrolysis displays rate accelerations of up to 3900 for tri-n-propyl orthoformate. Kinetic analysis shows that the mechanism of hydrolysis with the supramolecular host obeys the Michaelis-Menten model.Mechanistic studies, including 13 C-labeling experiments, revealed that the resting state of the catalytic system is the neutral substrate encapsulated in the host. Activation parameters for the k cat step of the reaction revealed that upon encapsulation in the assembly, the entropy of activation becomes more negative in contrast to the uncatalyzed reaction. Furthermore, solvent isotope effects reveal a normal k(H 2 O)/k(D 2 O) = 1.6, confirming that proton transfer is occurring in the transition state and is rate limiting in the catalyzed reaction. In comparison to the uncatalyzed reaction, which operates by an A-1 mechanism in which the decomposition of the protonated substrate is rate limiting, the encapsulated reaction proceeds through an A-S E 2 mechanism in which proton transfer from protonated water to the substrate is rate limiting.

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Section: Resultsmentioning

confidence: 99%

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

et al. 2009

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“…For this reason the enthalpy of the transition spans the value of ca. Δ H ≈ 3−6 kJ mol -1 and the transition temperature ranges as T c = 100−200 K. For example, in the complex [Fe(pybzim) 3 ](ClO 4 ) 2 ·H 2 O, where pybzim = 2,2‘-pyridine-benzimidazol, the presence of three rigid bidentate ligands results in the values of Δ H = 3.3 kJ mol -1 , Δ S = 23.2 J K -1 mol -1 , and T c = 142 K …”

Section: Discussionmentioning

confidence: 99%

Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K

et al. 2001

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The spin crossover system, [Fe(bzimpy)(2)](ClO(4))(2).0.25H(2)O, was reinvestigated above room temperature (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at T(c) = 403 K. Liberation of a fractional amount of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of DeltaT = 12 K. The existence of the hysteresis at such high temperature determines that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) separations (10 A). The high cooperativeness has been assigned to a perfect pi-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 A. Variable-temperature IR data and the heat capacity measurements match well the magnetic data. The thermodynamic properties are DeltaH = 17 kJ mol(-)(1), DeltaS = 43 J K(-)(1) mol(-)(1), so that the entropy of the spin transition shows a considerable contribution from the molecular vibrations. A theoretical model has been applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.

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“…Most of these changes have been attributed to changes of metal-ligand and intraligand bond distances and angles, with the Fe-N bond being the dominant contributor. Additional changes in the high energy (EXAFS) region were also clearly observed, which likewise point to a significant Fe-N bond change [22,23,[55][56][57]. and EXAFS spectra was carried out in two ways: i) fitting an excited state EXAFS spectrum that was generated from the transient spectrum, and the prior knowledge of the photolysis yield [58], as shown in figure 5a; ii) fitting directly the transient spectrum in energy space as described in ref.…”

Section: Structure Of the High Spin Statementioning

confidence: 99%

Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies

Cannizzo

Milne

Consani

et al. 2010

Coordination Chemistry Reviews

265

278

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The light-induced ultrafast spin and structure changes upon excitation of the singlet metal-toligand-charge-transfer (1 MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([Fe II (bpy) 3 ] 2+) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence upconversion, transient absorption studies in the 290-600 nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the 1 MLCT state from the singlet low spin ground state (1 GS) as the following sequence: 1,3 MLCT→ 5 T→ 1 GS, which does not involve intermediate singlet and triplet ligand field states. The population time of the HS state is found to be~150 fs, leaving it in a vibrationally hot state that relaxes in 2-3 ps, before decaying to the ground state in 650 ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe-N bond elongation in the high spin state, Fe-N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [Fe II (bpy) 3 ] 2+ are of general validity to the entire family of Fe(II)-polypyridine complexes.

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Spin crossover in iron(II) tris(2-(2-pyridyl)benzimidazole) complex monitored by the variable temperature EXAFS

Cited by 16 publications

References 19 publications

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Spin Equilibria in Monomeric Manganocenes: Solid-State Magnetic and EXAFS Studies

Strong Cooperativeness in the Mononuclear Iron(II) Derivative Exhibiting an Abrupt Spin Transition above 400 K

Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies

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