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, Akifumi; Ishida, Takayuki

doi:10.3390/inorganics5030052

Cited by 29 publications

(32 citation statements)

References 42 publications

(60 reference statements)

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“…Ishida and Kimura [135] reported the solution properties of the Fe(II) complexes of oxazolylpyridines (L33, Scheme 5) with a Cl substituent in the pyridine. Results from the application of the Evans method showed SCO in acetone solution with a T 1/2 at 270 K. The authors concluded, when Cl was substituted by other groups, that electron-donating groups suppress T 1/2 while electron-withdrawing groups raise T 1/2 .…”

Section: Results Solutionmentioning

confidence: 99%

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Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

2020

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The capability of a given substance to change its spin state by the action of a stimulus, such as a change in temperature, is by itself a very challenging property. Its interest is increased by the potential applications and the need to find sustainable functional materials. 3D transition metal complexes, mainly with octahedral geometry, display this property when coordinated to particular sets of ligands. The prediction of this behavior has been attempted by many authors. It is, however, made very difficult because spin crossover (SCO), as it is called, occurs most often in the solid state, where besides complexes, counter ions, and solvents are also present in many cases. Intermolecular interactions definitely play a major role in SCO. In this review, we decided to analyze SCO in mono- and binuclear transition metal complexes containing halogens as ligands or as substituents of the ligands. The aim was to try and find trends in the properties which might be correlated to halogen substitution patterns. Besides a revision of the properties, we analyzed structures and other information. We also tried to build a simple model to run Density Functional Theory (DFT) calculations and calculate several parameters hoping to find correlations between calculated indices and SCO data. Although there are many experimental studies and single-crystal X-ray diffraction structures, there are only few examples with the F, Cl, Br and series. When their intermolecular interactions were not very different, T1/2 (temperature with 50% high spin and 50% low spin states) usually increased with the calculated ligand field parameter (Δoct) within a given family. A way to predict SCO remains elusive.

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Section: Results Solutionmentioning

confidence: 99%

“…Ishida and Kimura [135] modified the bpp ligand by replacing pyrazole by oxazoline groups (L33). This new ligand presented several substituents on the pyridine group, one of them being chloride.…”

Section: Methodsmentioning

confidence: 99%

Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

2020

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“…The structural distortion is known to regulate T 1/2 to a considerable extent. 16,30−32 The solution experiments will afford a better venue for the discussion on the substituent effect.…”

Section: Resultsmentioning

confidence: 99%

“…The introduction of substituents will bring about drastic SCO tuning through the covalent bonds, in comparison with the effects through intermolecular interaction from counter ions and/or solvent molecules incorporated. A part of the experimental data has been communicated and clarified to undergo near-room-temperature SCO with X = H, Cl, Ph, CH 3 O, CH 3 S, 16 3-thienyl (3Th), and 4-pyridyl (4Py). 17 The magnetic susceptibility measurements were performed in solution to purge intermolecular interactions and rigid crystal lattice effects, and discussion can be focused on the substituent effect.…”

Section: Introductionmentioning

confidence: 99%

Spin-Crossover Temperature Predictable from DFT Calculation for Iron(II) Complexes with 4-Substituted Pybox and Related Heteroaromatic Ligands

Kimura

Ishida

2018

ACS Omega

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Spin-crossover (SCO) is a reversible transition between low and high spin states by external stimuli such as heat. The SCO behavior and transition temperature ( T 1/2 ) of a series of [Fe II (X-pybox) 2 ](ClO 4 ) 2 were studied to establish a methodology for ligand-field engineering, where X-pybox stands for 2,6-bis(oxazolin-2-yl)pyridine substituted with X at the 4-position of the pyridine ring. We utilized X = MeO, Me, 3-thienyl, Ph, H, MeS, 2-thienyl, N 3 , Cl, Br, 3-pyridyl, and 4-pyridyl. The solution susceptometry on five new derivatives with X = Me, 2-thienyl, N 3 , Br, and 3-pyridyl was performed in acetone, giving the SCO temperatures of 220, 260, 215, 280, and 270 K, respectively. The density-functional-theory molecular orbital (MO) calculation was performed on the ligands with geometry optimization. The atomic charge on the pyridine nitrogen atom [ρ(N py )] was extracted from the natural orbital population analysis. Positive correlation appeared in the T 1/2 versus ρ(N py ) plot with R 2 = 0.734, being consistent with the analysis using the Hammett substituent constants (σ p and σ p + ). This finding well agrees with the mechanism proposed: the rich electron density lifts the t 2g energy level through the dπ–pπ interaction, resulting in a narrow t 2g –e g energy gap and favoring the high-spin state and low T 1/2 . The MO method was successfully applied to the known SCO-active iron(II) compounds involving 4-substituted 2,6-bis(pyrazol-1-yl)pyridines. A distinct positive correlation appeared in the T 1/2 versus ρ(N py ) plot. The comparison of correlation coefficients indicates that ρ(N py ) is a more reliable parameter than σ p or σ p + to predict a shift of T 1/2 . Furthermore, this method can be more generalized by application to another known SCO family having 3-azinyl-4- p -tolyl-5-phenyl-1,2,4-triazole ligand series, where azinyl stands for a 2-azaaromatic ring. A good linear correlation was found in the T 1/2 versus ρ(N A ) plot (N A is the ligating nitrogen atom in the azaaromatic ring). Finally, we will state a reason why the present treatment is competent to predict the SCO equilibrium position only by consideration on the electronic perturbation.

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“…Recently, we and other groups discovered SCO in [Fe(pybox) 2 ] 2 + complexes and investigated the influences on spin state properties from structural aspects including ligand substituents, counter anions, solvents, and chirality. [34][35][36][37][38][39][40] Owing to the intrinsic advantages of pybox ligands such as facile synthesis, easiness of structural modification with functional units, and excellent luminescent properties, [41][42][43] we attempt to decorate fluorophore, pyrene moiety, to pybox ligand and construct an SCO-fluorescence bifunctional compound. In our design of ligand, the pyrene moiety is conjugately linked to 4positon of pyridine ring of pybox ligand.…”

Section: Introductionmentioning

confidence: 99%

Construction of Magneto‐Fluorescent Bifunctional Spin‐Crossover Fe(II) Complex from Pyrene‐Decorated Pybox Ligand

et al. 2021

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The construction of magneto-fluorescent bifunctional complexes is a feasible approach toward multifunctional molecular materials. Herein we report the synthesis and properties studies of a mononuclear Fe(II) complex [FeL 2 ](ClO 4 ) (1), where L is a pyridine-2,6-bis(oxazoline) (pybox) ligand decorated by the pyrene fluorophore. Magnetic susceptibility measurement of desolvated complex 1-d shows an incomplete and gradual spin-crossover in the temperature range 50-300 K, which is further confirmed via 57 Fe Mössbauer spectroscopy study. Light-induced excited spin state trapping (LIESST) is also observed below 70 K when the powder sample is irradiated by a 532 nm laser. The change in absorption during the spin-crossover (SCO) process is investigated via the temperature-dependent UV-vis spectroscopy. As expected, through introducing the chromophore, 1 displays fluorescence in both solution and solid state, achieving the coexistence of spin-crossover and fluorescence in one compound.

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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)

Cited by 29 publications

References 42 publications

Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

Spin Crossover in 3D Metal Centers Binding Halide-Containing Ligands: Magnetism, Structure and Computational Studies

Spin-Crossover Temperature Predictable from DFT Calculation for Iron(II) Complexes with 4-Substituted Pybox and Related Heteroaromatic Ligands

Construction of Magneto‐Fluorescent Bifunctional Spin‐Crossover Fe(II) Complex from Pyrene‐Decorated Pybox Ligand

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