Spin crossover and reversible single-crystal to single-crystal transformation behaviour in two cyanide-bridged mixed-valence {FeIII2FeII2} clusters

Zheng, Chunyang; Xu, Juping; Wang, Feng; Tao, Jun; Li, Dongfeng

doi:10.1039/c6dt03436e

Cited by 47 publications

(29 citation statements)

References 71 publications

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“…At 250 K, the 57 Fe Mössbauer spectrum of solid 2 shows a high-spin Fe(II) species comprising 46(5)% of the sample with an isomer shift (δ) of 0.880(9) mm/s and quadrupole splitting (Δ E Q ) of 3.22(2) mm/s (Figure A, green). ,− The remaining sample has a broad, poorly resolved signal (blue) potentially composed of multiple sites with an δ of 0.23(2) mm/s and Δ E Q of 0.81(2) mm/s which we assign as low-spin Fe(II) sites. These parameters are outside of the typical ranges for both low-spin Fe(II) (δ: 0.36–0.52 mm/s; Δ E Q : 0.23–0.52 mm/s) and low-spin Fe(III) (δ: 0.20–0.28 mm/s; Δ E Q : 1.5–1.7 mm/s) reported for TPA ligated 6-coordinate complexes but are similar to other low-spin Fe(II) species …”

Section: Results and Discussionmentioning

confidence: 99%

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

et al. 2020

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Organic diradicals are uncommon species that have been intensely studied for their unique properties and potential applicability in a diverse range of innovative fields. While there is a growing class of stable and well characterized organic diradicals, there has been recent focus on how diradical character can be controlled or modulated with external stimuli. Here we demonstrate that a diiron complex bridged by the doubly oxidized ligand tetrathiafulvalene-2,3,6,7tetrathiolate (TTFtt 2−) undergoes a thermally induced Fe-centered spin-crossover which yields significant diradical character on TTFtt 2−. UV-vis-Near-IR, Mössbauer, NMR, and EPR spectroscopies with magnetometry, crystallography, and advanced theoretical treatments suggest that this diradical character arises from a shrinking TTFtt 2− π-manifold from the Fe(II)-centered spin-crossover. The TTFtt 2− centered diradical is predicted to have a singlet ground state by theory and variable temperature EPR. This unusual phenomenon demonstrates that inorganic spin transitions can be used to modulate organic diradical character. Results and Discussion Synthesis and Structural Parameters Complex 1 was synthesized via reaction with the deprotected proligand 2,3,6,7-tetrakis(2cyanoethylthio)tetrathiafulvalene (TTFtt(C2H4CN)4) in good yield. Complex 1 was insoluble in all solvents we investigated which precluded detailed characterization but is pure as indicated by combustion analysis and behaves as a suitable synthon for subsequent chemistry. Complex 1 can be doubly oxidized with [Cp2Fe][BAr F 4] to form 2 which is more soluble, enabling common solution characterization including 1 H NMR and cyclic voltammetry measurements (Figure S1-S2). Oxidation from 1 to 2 could be ligandcentered (TTFtt 4− →TTFtt 2−), metal-centered (2 Fe(II)→2 Fe(III)), or some intermediate case, but the data acquired for 2 supports a TTFtt 2− structure arising from ligandcentered oxidation (Chart 1B, see below). Compound 2 was structurally characterized via singlecrystal X-ray diffraction (SXRD) at 293 K (2-HT; Figure S3) and 100 K (2-LT; Figure 1). In both structures TTFtt 2− is bridged between two TPA-capped Fe centers with two outer-sphere BAr F 4 − counter anions. The most striking difference between these temperatures is markedly longer Fe bond lengths in 2-HT. The Fe-Npyridine and Fe-Namine bond lengths in 2-LT are 1.958(6)-1.979(6) and 2.017(6) Å (Figure 1), respectively. These values are consistent with Fe-N bonds in other low-spin complexes with a Fe-TPA moiety. 16,17 In 2-HT, these bonds are 0.18-0.19 and 0.244(11) Å longer than their counterparts at 100 K, respectively, and are consistent with high-spin Fe-TPA complexes. The shorter Fe bonds at lower temperature indicate that 2 exhibits a temperature dependent spincrossover as observed in related compounds. 16,21

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Section: Results and Discussionmentioning

confidence: 99%

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

et al. 2020

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“…For SCO complexes, an abrupt spin transition at room temperature with a wide hysteresis is one of the most important requirements from the viewpoint of applications . Currently, it is still a great challenge to design and prepare systems that exhibit SCO around room temperature. , In 2008, Gao et al reported an Fe(II) SCO complex of tridentate pyridyl aroylhydrazones with the transition temperature ( T c ) of room temperature . Subsequent research indicates that Fe(II) pyridyl aroylhydrazones are good candidates for high T c SCO materials .…”

Section: Introductionmentioning

confidence: 99%

Rhodamine 6G-Labeled Pyridyl Aroylhydrazone Fe(II) Complex Exhibiting Synergetic Spin Crossover and Fluorescence

et al. 2018

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Here, we use a pyridinecarbaldehyde rhodamine 6G hydrazone ligand (L) to synthesize an Fe(II) complex 1 for the search of new fluorescent-spin crossover (SCO) materials. Single-crystal structural determinations suggest that the Fe(II) ion is chelated by two ring-opened ligands (L-o) to form a FeNO coordination environment, and intermolecular π---π contacts of the xanthene groups connect the adjacent molecules to form a supramolecular one-dimensional chain. Magnetic susceptibility measurements on complex 1 show that three-step SCO takes place in the temperature range of 120-350 K, and its desolvated form 1-d exhibits SCO around room temperature ( T↑ = 343 K and T↓ = 303 K) with a wide hysteresis loop of 40 K. Moreover, complex 1-d displays light-induced excited spin-state trapping phenomenon. Intriguingly, the fluorescence intensity of the maximum emission at 560 nm for complex 1-d displays discontinuous variation in the range of 250-400 K, indicative of the occurrence of synergetic fluorescence and SCO.

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“…[11] Nevertheless, an increasing number of interesting examples of Prussian blue molecular polymetallic assemblies have been reported due to the fact that they usually exhibit both optical and magnetic bistability which arises from a reversible metal-to metal charge transfer between the Co III (or Fe III ) and the Fe II centres. This family of compounds include pentanuclear trigonal bipyramidal{Fe II 2 /Fe III 3 } and {Fe II 2 /Co III 3 }units, [12,13] octanuclear cubic{Fe II /Fe III } 4 and {Fe II /Co III } 4 assemblies, [14,15] homonuclear {Fe II /Fe III } 2 squares, [16,17] and a significant number of heterotetranuclear square complexes {Fe II /Co III } 2 . [11,18,19] Recently, we have reported the preparation of the diamagnetic cyanido-bridged [{Co III {(Me) 2 (µ-ET)cyclen}} 2 {(µ-NC) 2 Fe II (CN) 4 } 2 ] 2square complex [20] via a mechanistically designed self-assembly reaction (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {Co^III/Fe^II}₂ Square

et al. 2018

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A kineticomechanistic study of reversible electron-transfer processes undergone by the water-soluble, cyanido-bridged mixed-valence [{Co{(Me)(μ-ET)cyclen}}{(μ-NC)Fe(CN)}] square has been carried out. The oxidation reaction consists of a two-step process with the participation of a solvent-assisted outer-sphere complex, as a result of the establishment of hydrogen bonds that involve the oxo groups of the oxidant (peroxodisulfate) and the terminal cyanido ligands of the tetrametallic square. The formally endergonic reduction reaction of the fully oxidized ([{Co{(Me)(μ-ET)cyclen}}{(μ-NC)Fe(CN)}]) core by water, producing hydrogen peroxide from water even at low pH values, is also a two-step process. Each one of these processes requires a set of two preequilibria involving the association of OH and its subsequent deprotonation by a further OH anion. The structure of the square compound in its fully protonated form has also been determined by X-ray diffraction and shows the existence of strong hydrogen-bonding interactions, in agreement with the rather high basicity of the terminal cyanido ligands. Likewise, density functional theory calculations on the tetrametallic complex showed zones with negative electrostatic potential around the Fe centers of the square that would account for the establishment of the hydrogen bonds found in the solid state. Spectroelectrochemistry experiments demonstrated the singular stability of the {Co/Fe} complex, as well as that of their partially, {Co/FeFe}, and fully, {Co/Fe}, oxidized counterparts because no hysteresis was observed in these measurements.

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Spin crossover and reversible single-crystal to single-crystal transformation behaviour in two cyanide-bridged mixed-valence {FeIII2FeII2} clusters

Cited by 47 publications

References 71 publications

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

Rhodamine 6G-Labeled Pyridyl Aroylhydrazone Fe(II) Complex Exhibiting Synergetic Spin Crossover and Fluorescence

Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {Co^III/Fe^II}₂ Square

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Spin crossover and reversible single-crystal to single-crystal transformation behaviour in two cyanide-bridged mixed-valence {FeIII2FeII2} clusters

Cited by 47 publications

References 71 publications

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

Reversible Switching of Organic Diradical Character via Iron-Based Spin-Crossover

Rhodamine 6G-Labeled Pyridyl Aroylhydrazone Fe(II) Complex Exhibiting Synergetic Spin Crossover and Fluorescence

Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {CoIII/FeII}2 Square

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Kineticomechanistic Study of the Redox pH Cycling Processes Occurring on a Robust Water-Soluble Cyanido-Bridged Mixed-Valence {Co^III/Fe^II}₂ Square