Substituent effect in spin-crossover behavior of iron(II)-Ar-pybox complexes (Ar-pybox = 4-aryl-2,6-bis(oxazolin-2-yl)pyridine)

Kimura, Akifumi; Ishida, Takayuki

doi:10.1063/1.5021938

Cited by 3 publications

(14 citation statements)

References 20 publications

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“…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. A plot of T 1/2 against the Hammett substituent constant σ p 18,19 exhibited a strong correlation with a positive slope, indicating that electron-donating (-releasing) groups suppress T 1/2 in this series.…”

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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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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“…As a result, it can be largely followed by solution NMR spectroscopy. The observed stabilization of the LS state by an electron-withdrawing group in this position of N , N ′-disubstituted 3-bpp mirrors the one occurring in iron(II) complexes with 1-bpp and other pyridine-based ligands …”

Section: Discussionmentioning

confidence: 54%

“…A decrease by almost 100 K following the substitution of the hydroxyl groups in [Fe( L OH ) 2 ](BF 4 ) 2 by the t -butyl groups in [Fe( L t ‑Bu ) 2 ](BF 4 ) 2 agrees with the stabilization of the HS state by an electron-donating substituent in this position of the 3-bpp ligand, as suggested in previous studies of iron(II) complexes with N , N ′-disubstituted 3-bpp. , With no interference from NH groups, this effect may have the same origin as does the stabilization of the HS state by an electron-donating substituent in the para-position of the pyridyl moiety. The latter lowers the midpoint temperature by stabilizing the e g level of the metal d-orbitals and leading to a narrower t 2g –e g energy gap. ,, For [Fe( L OH ) 2 ](BF 4 ) 2 , an opposite electronic effect of the p -cyanophenyl group shifts the SCO observed in a solution of the complex [Fe( L ) 2 ](ClO 4 ) 2 (Table ) to higher temperatures and thereby produces the SCO perfectly centered at room temperature (22 °C).…”

Section: Resultsmentioning

confidence: 99%

“…Such studies allowed identifying a thermally induced SCO centered at ,,− or slightly above , room temperature in solutions of few coordination compounds. There are, however, fewer examples of an SCO that is almost complete ,,, in the accessible temperature range (such as accessed in a large series of different solvents or followed by UV–vis spectroscopy , and SQUID-magnetometry).…”

Section: Introductionmentioning

confidence: 99%

“…To bring this SCO closer to room temperature, an electron-withdrawing substituent such as a p -cyanophenyl group introduced into the para-position of the pyridyl moiety of the same ligand may help. Based on “structure–property” relations for iron(II) complexes of isomeric bis(pyrazol-1-yl)pyridines (1-bpp) and other pyridine-based ligands, it should strengthen the ligand field and thereby stabilize the LS state of the iron(II) ion, shifting the SCO to higher temperatures. The proposed modification to N , N ′-disubstituted 3-bpp (Chart ) allowed designing an almost complete SCO centered at room temperature that can be followed by NMR spectroscopy using two different solvents; an additional motivation was to probe the solvent effect on the SCO behavior of otherwise HS ,− complexes.…”

Section: Introductionmentioning

confidence: 99%

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Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with N,N′-Disubstituted Bis(pyrazol-3-yl)pyridines

et al. 2021

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Here, we report a combined study of the effects of two chemical modifications to an N,N′-disubstituted bis(pyrazol-3-yl)pyridine (3-bpp) and of different solvents on the spin-crossover (SCO) behavior in otherwise high-spin iron(II) complexes by solution NMR spectroscopy. The observed stabilization of the low-spin state by electron-withdrawing substituents in the two positions of the ligand that induce opposite electronic effects in SCO–active iron(II) complexes of isomeric bis(pyrazol-1-yl)pyridines (1-bpp) was previously hidden by NH functionalities in 3-bpp precluding the molecular design of SCO compounds with this family of ligands. With the recent SCO-assisting substituent design, the uncovered trends converged toward the first iron(II) complex of N,N′-disubstituted 3-bpp to undergo an almost complete SCO centered at room temperature in a less polar solvent of a high hydrogen-bond acceptor ability.

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Identification-Robust Subvector Inference

Andrews¹

2017

SSRN Journal

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Substituent effect in spin-crossover behavior of iron(II)-Ar-pybox complexes (Ar-pybox = 4-aryl-2,6-bis(oxazolin-2-yl)pyridine)

Cited by 3 publications

References 20 publications

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

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

Room-Temperature Spin Crossover in a Solution of Iron(II) Complexes with N,N′-Disubstituted Bis(pyrazol-3-yl)pyridines

Identification-Robust Subvector Inference

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