Unprecedented bistability domain and interplay between spin crossover and polymorphism in a mononuclear iron(ii) complex

Bushuev, Mark B.; Daletsky, Vasiliy A.; Pishchur, Denis P.; Gatilov, Yuri V.; Корольков, И. В.; Николаенкова, Елена Б.; Krivopalov, V. P.

doi:10.1039/c3dt53440e

Cited by 35 publications

(24 citation statements)

References 49 publications

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“…However, when m = 14, the compound is low spin at room temperature but shows a small, irreversible increase in χ M T upon warming to 350 K, consistent with a low-spin → high-spin conversion in about 10% of the sample. This may be associated with loss of lattice water from the material, which occurs around 340 K by DSC and TGA (see below). , Finally, [Fe(L 3 C 12 ) 2 ][BF 4 ] 2 · x H 2 O is the only solid compound with a significant high-spin population at room temperature when it is freshly isolated. Its χ M T value of 2.2 cm 3 mol –1 K at 300 K implies that ca.…”

Section: Resultsmentioning

confidence: 99%

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes

et al. 2018

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Two series of 4-(alkoxyphenyl) 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (L3R) or alkyl 2,6-bis{pyrazol-1-yl}pyridine-4-carboxyate (L4R) esters have been synthesized and complexed to iron(II), where R = C n H2n+1 (n = 6, 12, 14, 16, 18); two other derivatives related to L3R are also reported. While the solid [Fe(L4R)2][BF4]2 compounds are isostructural by powder diffraction and show similar spin state behaviors, the [Fe(L3R)2][BF4]2 series shows more varied structures and magnetic properties. This was confirmed by solvated crystal structures of [Fe(L3R)2][BF4]2 with n = 6, 14, 16, which all adopt the P1̅ space group but show significantly different side-chain conformations and/or crystal packing. The solid complexes are mostly low spin at room temperature, with many exhibiting the onset of thermal spin crossover (SCO) upon warming. Heating the complexes with n ≥ 14 significantly above their SCO temperature transforms them irreversibly into a predominantly high spin state, which is accompanied by structure changes and loss of crystallinity by powder diffraction. These transformations do not coincide with lattice solvent loss and may reflect melting and refreezing of their alkyl chain conformations during the thermal cycle. Four of the complexes exhibit SCO in CD3CN solution with T 1/2 = 273–277 K, which is apparently unaffected by their alkyl chain substituents.

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Section: Resultsmentioning

confidence: 99%

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes

et al. 2018

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“…[6] While examples with hysteresis widths of up to 140 Ka re known, [13] SCO materials showingh ysteresis wider than 40 Ka re still unusual. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] As ar esult, most SCO application studies are carriedo ut with just two types of coordination polymer materials, with suitably hysteretic SCO that also spans room temperature. [28,29] Studies of the structuralb asis underlying SCO hysteresis are hampered by challenges in structurally characterisings uch materials.…”

Section: Introductionmentioning

confidence: 99%

“…Most such applications require compounds exhibiting abrupt thermal SCO with significant thermal hysteresis, which are bistable at temperatures inside the hysteresis loop . While examples with hysteresis widths of up to 140 K are known, SCO materials showing hysteresis wider than 40 K are still unusual . As a result, most SCO application studies are carried out with just two types of coordination polymer materials, with suitably hysteretic SCO that also spans room temperature …”

Section: Introductionmentioning

confidence: 99%

Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin‐Crossover Compound From its Copper(II) and Zinc(II) Congeners

Pask

Greatorex

Kulmaczewski

et al. 2020

Chemistry A European J

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Annealing [FeL2][BF4]2⋅2 H2O (L=2,6‐bis‐[5‐methyl‐1H‐pyrazol‐3‐yl]pyridine) affords an anhydrous material, which undergoes a spin transition at T1/2=205 K with a 65 K thermal hysteresis loop. This occurs through a sequence of phase changes, which were monitored by powder diffraction in an earlier study. [CuL2][BF4]2⋅2 H2O and [ZnL2][BF4]2⋅2 H2O are not perfectly isostructural but, unlike the iron compound, they undergo single‐crystal‐to‐single‐crystal dehydration upon annealing. All the annealed compounds initially adopt the same tetragonal phase but undergo a phase change near room temperature upon re‐cooling. The low‐temperature phase of [CuL2][BF4]2 involves ordering of its Jahn–Teller distortion, to a monoclinic lattice with three unique cation sites. The zinc compound adopts a different, triclinic low‐temperature phase with significant twisting of its coordination sphere, which unexpectedly becomes more pronounced as the crystal is cooled. Synchrotron powder diffraction data confirm that the structural changes in the anhydrous zinc complex are reproduced in the high‐spin iron compound, before the onset of spin‐crossover. This will contribute to the wide hysteresis in the spin transition of the iron complex. EPR spectra of copper‐doped [Fe0.97Cu0.03L2][BF4]2 imply its low‐spin phase contains two distinct cation environments in a 2:1 ratio.

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“…The widest known such hysteresis loop, at the time of writing, is exhibited by 1 (Scheme 1). 24 Compound 1 is isolated as a low-spin hemihydrate material 1¢xH 2 O (x µ 0.5). Heating the sample removes the lattice water, affording three different anhydrous phases depending on the annealing temperature.…”

Section: Molecular Compounds Showing Wide and Symmetric Thermal Hystementioning

confidence: 99%

Spin-crossover Compounds with Wide Thermal Hysteresis

2014

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Spin-crossover compounds showing wide thermal hysteresis are surveyed, and the factors underlying these properties are discussed. Hysteresis is promoted by large structural rearrangements during the transition and by strong intermolecular interactions involving rigid ligand groups or donor atoms. These observations provide new principles for the design of molecular crystals undergoing spin crossover (or other phase changes) with predefined switching properties.

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Unprecedented bistability domain and interplay between spin crossover and polymorphism in a mononuclear iron(ii) complex

Cited by 35 publications

References 49 publications

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes

2,6-Bis(pyrazol-1-yl)pyridine-4-carboxylate Esters with Alkyl Chain Substituents and Their Iron(II) Complexes

Elucidating the Structural Chemistry of a Hysteretic Iron(II) Spin‐Crossover Compound From its Copper(II) and Zinc(II) Congeners

Spin-crossover Compounds with Wide Thermal Hysteresis

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