The Nature of Spin Crossover and Coordination Core Distortion in a Family of Binuclear Iron(II) Complexes with Bipyridyl‐Like Bridging Ligands

Matouzenko, Galina S.; Jeanneau, Erwann; Verat, Alexander Yu.; Gaetano, Yannick De

doi:10.1002/ejic.201101178

Cited by 33 publications

(43 citation statements)

References 61 publications

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“…As Figure 4a exemplifies, the CShM vs. σ p plot has a relation with a negative slope, implying that the electron-donating group would favor a distorted structure. Such distortion would bring about preference for the HS states due to reduction of the ligand-field strength [42][43][44][45] and suppress the SCO temperature. Gao and co-workers have already reported the SCO study on a [Fe(H-pybox) 2 ] 2+ series with counter anion and solvent variation [25] with the substituent X fixed to H, and the magneto-structural relation was clarified to give a partially similar conclusion: highly distorted structures are favorable for the HS state and only intermediately distorted compounds show SCO.…”

Section: Coordination Structure Effectmentioning

confidence: 99%

Pybox-Iron(II) Spin-Crossover Complexes with Substituent Effects from the 4-Position of the Pyridine Ring (Pybox = 2,6-Bis(oxazolin-2-yl)pyridine)

Kimura

Ishida

2017

Inorganics

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Spin-crossover (SCO) behavior of a series of [Fe(X-pybox) 2 ](ClO 4 ) 2 was investigated, where X-pybox stands for 4-X-substituted 2,6-bis(oxazolin-2-yl)pyridine with X = H, Cl, Ph, CH 3 O, and CH 3 S. We confirmed that the mother compound [Fe(H-pybox) 2 ](ClO 4 ) 2 underwent SCO above room temperature. After X was introduced, the SCO temperatures (T 1/2 ) were modulated as 310, 230, and 330 K for X = Cl, Ph, and CH 3 S, respectively. The CH 3 O derivative possessed the high-spin state down to 2 K. Crystallographic analysis for X = H, Cl, CH 3 O, and CH 3 S was successful, being consistent with the results of the magnetic study. Distorted coordination structures stabilize the HS (high-spin) state, and the highest degree of the coordination structure distortion is found in the CH 3 O derivative. A plot of T 1/2 against the Hammett substituent constant σ p showed a positive relation. Solution susceptometry was also performed to remove intermolecular interaction and rigid crystal lattice effects, and the T 1/2 's were determined as 260, 270, 240, 170, and 210 K for X = H, Cl, Ph, CH 3 O, and CH 3 S, respectively, in acetone. The substituent effect on T 1/2 became very distinct, and it is clarified that electron-donating groups stabilize the HS state.

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Section: Coordination Structure Effectmentioning

confidence: 99%

Pybox-Iron(II) Spin-Crossover Complexes with Substituent Effects from the 4-Position of the Pyridine Ring (Pybox = 2,6-Bis(oxazolin-2-yl)pyridine)

Kimura

Ishida

2017

Inorganics

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“…Temperature-dependent magnetic measurements of the 1D isomer [Fe(NCS) 2 (4-Acpy) 2 ] n at 200 Oe reveal antiferromagnetic ordering at T N = 4.5 K. Field-dependent measurements show a metamagnetic transition into a saturated paramagnetic phase at a critical field of ca. 700 Oe.…”

Section: Introductionmentioning

confidence: 96%

“…Coordination polymers based on metal cations with unpaired electrons are of increasing interest, because of their different magnetic properties, such as spin-crossover or low-dimensional magnetism. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] In several cases, the metal cations are linked by small, two-or three-atom ligands (e.g., cyanide or azide anions) into coordination networks of different dimensionality, and some examples are given in refs. [17][18][19][20][21][22][23][24][25][26][27][28][29] In this regard, thiocyanato anions are also of interest because of their ambidentate nature and versatile coordination modes.…”

Section: Introductionmentioning

confidence: 99%

Thiocyanato Coordination Polymers with Isomeric Coordination Networks – Synthesis, Structures, and Magnetic Properties

et al. 2015

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In this work we present the vibrationally resolved optical absorption spectrum of p‐hydroxybenzylidene‐2,3‐dimethylimidazolinone (HBDI), the green fluorescent protein (GFP) chromophore, computed at several levels of theory, including time‐dependent DFT with various functionals and basis sets, CASSCF, CASPT2 and XMCQDPT2. We also investigated what happens to the spectrum if the ground‐ and excited‐state geometries are optimized at different levels of theory (mixed approach), as has been used previously. The vibrationally resolved absorption spectra obtained by DFT, CASPT2 and XMCQDPT2 are very similar and consist of a main absorption peak and a shoulder that is ∼1500 cm−1 higher in energy. The vibrational progression increases moderately with temperature. These spectra are in qualitative agreement with experimental action spectra, but much narrower and lack the long tail in the blue, even at high temperatures. Because our calculated emission spectra, which are equally narrow, are in good agreement with the emission of green fluorescent protein at 253 K, we argue that the action spectrum are too broad to be considered as the absorption spectrum. The CASSCF method and the mixed approaches overestimate the vibrational progressions with respect to CAM‐B3LYP, CASPT2 and XMCQDPT2, due to inaccuracies in the geometric S0→S1 displacements. Finally, we computed the vibronic spectra of four chromophore analogues with different substitutions on the rings and found that these substitutions hardly affect the lineshape in vacuum.

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“…[25][26][27] It has been shown that serious differences in the degree of distortion of FeN 6 chromophore geometries can lead to various spin-crossover behaviors: One-step, twostep, or incomplete (50 %) transitions. On the other hand, our investigations of 3D network [Fe(qbtr) 3 ](ClO 4 ) 2 containing flexible ligand bridges did not reveal any influence of conformational alterations on the FeN 6 geometry.…”

Section: Resultsmentioning

confidence: 99%

“…[19] It is also assumed that in dinuclear complexes containing crystallographically unique iron(II) ions, intermolecular interactions influence spin-crossover properties leading to the occurrence of an intermediate phase comprising LS-HS or 50 % HS-HS and 50 % LS-LS pairs. [24] Investigations of dinuclear complexes based on 1,2-bis(4-pyridyl)ethane, [25] bis(2-picolyl)amine, [26] and 1,2-bis(4-pyridyl)ethyne [27] showed that a degree of distortion in the [FeN 6 ] chromo-phore caused by ligand strain and packing effects is responsible for spin-crossover (SCO) behavior. It is worth noting that the number of steps in the spin-transition curve does not necessarily match the number of crystallographically distinct iron(II) ions in a crystal lattice.…”

Section: Introductionmentioning

confidence: 99%

Two‐Step Spin Transition in an Iron(II) Coordination Network Based on Flexible Bitopic Ligand 1‐(Tetrazol‐1‐yl)‐3‐(1,2,3‐triazol‐1‐yl)propane

et al. 2012

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Flexible bitopic ligand 1‐(tetrazol‐1‐yl)‐3‐(1,2,3‐triazol‐1‐yl)propane (ptrtz) reacts with Fe(ClO4)2·6H2O to form two‐dimensional (2D) coordination network [Fe(ptrtz)3](ClO4)2·MeCN (1) in which two chemically different spin crossover (SCO) FeII centers are observed. Although two 1,2,3‐triazole and four tetrazole rings are in the first coordination sphere of the Fe1 ions, Fe2 ions are coordinated to four 1,2,3‐triazole and two tetrazole rings. Symmetry‐related FeII ions are bridged by two disordered ptrtz molecules resulting in the formation of chains that are extended in the same direction. Alternately arranged chains containing Fe1 or Fe2 ions are cross‐linked by single ptrtz molecules to form 2D layers. At room temperature, the complex remains in a high‐spin (HS) form (χMT = 3.46 cm3 K mol–1). Spin crossover in 1 occurs in two steps separated by an inflection point at 140 K (χMT = 2.68 cm3 K mol–1, γHS ≈ 0.76). The first step is gradual and between 220 and 140 K about a quarter of all the iron(II) ions change their spin state (T1↓ = T1↑ = 165 K). Single‐crystal X‐ray diffraction studies revealed that upon lowering the temperature from 220 to 140 K, spin crossover occurs for only half of the iron(II) ions occupying Fe2 sites. It is accompanied by an alteration of the occupancy factor of ptrtz molecules bridging the Fe2 ions. Iron(II) ions occupying Fe1 sites remain in the HS form, which inhibits compression of the polymeric layer in the Fe1···Fe1 and Fe2···Fe2 linking direction. Upon further lowering the temperature, iron(II) ions occupying Fe1 sites and the rest of the iron(II) ions occupying Fe2 sites change their spin state. The second step of the spin transition is very abrupt and is accompanied by a hysteresis loop (T2↓ = 90 K, T2↑ = 96 K). The change in the spin state by iron(II) ions occupying Fe1 and Fe2 sites involves, contrary to first step, a significant shortening of the Fe1···Fe1 and Fe2···Fe2 separations.

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The Nature of Spin Crossover and Coordination Core Distortion in a Family of Binuclear Iron(II) Complexes with Bipyridyl‐Like Bridging Ligands

Cited by 33 publications

References 61 publications

Pybox-Iron(II) Spin-Crossover Complexes with Substituent Effects from the 4-Position of the Pyridine Ring (Pybox = 2,6-Bis(oxazolin-2-yl)pyridine)

Pybox-Iron(II) Spin-Crossover Complexes with Substituent Effects from the 4-Position of the Pyridine Ring (Pybox = 2,6-Bis(oxazolin-2-yl)pyridine)

Thiocyanato Coordination Polymers with Isomeric Coordination Networks – Synthesis, Structures, and Magnetic Properties

Two‐Step Spin Transition in an Iron(II) Coordination Network Based on Flexible Bitopic Ligand 1‐(Tetrazol‐1‐yl)‐3‐(1,2,3‐triazol‐1‐yl)propane

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