Tridentate facial coordination mode of an unsymmetrical tetradentate diazine ligand in an iron(III) complex

Sreerama, Subramanya Gupta; Mukhopadhyay, Abhik; Pal, Samudranil

doi:10.1016/j.inoche.2006.07.003

Cited by 4 publications

(3 citation statements)

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“…The average distances of the bonds Fe III –O phenolate (1.8651 Å), Fe III –N imine (1.9401 Å) and Fe III –N amine (2.049 Å) are consistent with the low-spin state of iron(III) in a pseudooctahedral geometry. Typically, octahedral LS distances of Fe III –O phenolate , Fe III –N imine , and Fe III –N amine are in the ranges 1.85–1.89, ,,, 1.92–1.96, ,,, and 2.02–2.08 Å, ,, respectively, whereas the corresponding distances for HS iron(III) are in the ranges 1.89–1.93, ,,,, 2.09–2.15, ,,, and 2.18–2.26 Å, ,,, respectively. These variations of bond distances with spin state are readily explained using MO theory which shows an antibonding (d σ *) HOMO in HS octahedral iron(III) complexes, but a nonbonding (d π ) HOMO in the corresponding LS complexes.…”

Section: Resultsmentioning

confidence: 99%

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

et al. 2012

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Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 Å) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and Mössbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and Mössbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ↔ (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).

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Section: Resultsmentioning

confidence: 99%

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

et al. 2012

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“…The zinc(II) complexes are naturally diamagnetic and exhibit no d-d transition; all their UV bands can be assigned to p-p* transitions of the azomethine chromophore of the ligands. (9) C (14) C (3,4) C (2,5,6,(10)(11)(12)(13) C (13) C (18) C (2,5,6,(10)(11)(12)(13)(14)(15)(16)(17) Table 5 UV-vis spectral data for the ligands and complexes a A 2 /A 1 = x/(100 -x) where A 1 = the absorbance of the phenol-imine form (p-p*); A 2 = the absorbance of the keto-amine form (n-p*); x = the percentage of ketoamine form b Keto-amine form 0% in basic medium. Basic medium is attained by addition of NEt 3 (1 mL) to the given solution (ligand concentration: 1 9 10 -5 mol dm -3 ) c Acidic medium is attained by addition of CF 3 COOH (1 mL) to the given solution (ligand concentration: …”

Section: Electronic Spectramentioning

confidence: 99%

“…The coordination chemistry of substituted hydrazones has received further impetus from applications such as anti-viral or anti-inflammatory agents in either the free ligands or their metal complexes [9]. Although symmetric diazine ligands have been extensively studied, there is no report on their complexes with bisSchiff bases of hydrazine which are asymmetrical with respect to the two chelating sites [10]. Crown ethers are of interest in the area of molecular recognition [11].…”

Section: Introductionmentioning

confidence: 99%

Synthesis and spectroscopic characterization of asymmetric Schiff bases derived from 4′-formylbenzo-15-crown-5 containing recognition sites for alkali and transition metal guest cations

Hayvalı

Yardimci

2008

Transition Met Chem

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Asymmetric salen-type Schiff base ligands have been synthesized via a stepwise approach. In the first step, mono-Schiff base compounds were prepared by condensation of salicylaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2-hydroxy-5-methoxybenzaldehyde and 2-hydroxy-1-naphthaldehyde with hydrazine hydrate. These compounds were then reacted with 4 0 -formylbenzo-15-crown-5 to prepare asymmetric ligands. 1 H-NMR spectra indicate that the mono-and asymmetric bis-Schiff base compounds exist in both (E) and (Z) isomeric forms in CDCl 3 solution. The asymmetric crown compounds form crystalline 1:1 (Na + :ligand) complexes with sodium perchlorate. Homo-metallic Ni(II) and Zn(II) complexes with 1:2 (metal:ligand) stoichiometries have also been synthesized. The results indicate that the Schiff base ligands coordinate through the azomethine nitrogen and phenolic oxygen.

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Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [Fe^III(5‐X‐salMeen)₂]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition

Al‐Azzani

Al-Mjeni

Mitsuhashi

et al. 2020

Chemistry A European J

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X‐ray structures of the halo‐substituted complexes [FeIII(5‐X‐salMeen)2]ClO4 (X=F, Cl, Br, I) [salMeen=N‐methyl‐N‐(2‐aminoethyl)salicylaldiminate]at RT have revealed the presence of two discrete HS complex cations in the crystallographic asymmetric unit with two perchlorate counter ions linking them by N−Hamine⋅⋅⋅Operchlorate interactions. At 90 K, the two complex cations are distinctly HS and LS, a rare crystallographic observation of this coexistence in the FeIII‐salRen (R=alkyl) spin‐crossover (SCO) system. At both temperatures, crystal packing shows dimerization through C−Himine⋅⋅⋅Ophenolate interactions, a key feature for SCO cooperativity. Moreover, there are noncovalent contacts between the complex cations through type‐II halogen‐halogen bonds, which are novel in this system. The magnetic profiles and Mössbauer spectra concur with the structural analyses and reveal 50 % SCO of the type [HS‐HS]↔[HS‐LS] with a broad plateau. In contrast, [FeIII(5‐Cl‐salMeen)2]BPh4⋅2MeOH is LS and exhibits a temperature‐dependent crystallographic phase transition, exemplifying the influence of lattice solvents and counter ions on SCO.

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Tridentate facial coordination mode of an unsymmetrical tetradentate diazine ligand in an iron(III) complex

Cited by 4 publications

References 36 publications

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

Synthesis and spectroscopic characterization of asymmetric Schiff bases derived from 4′-formylbenzo-15-crown-5 containing recognition sites for alkali and transition metal guest cations

Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [Fe^III(5‐X‐salMeen)₂]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition

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Tridentate facial coordination mode of an unsymmetrical tetradentate diazine ligand in an iron(III) complex

Cited by 4 publications

References 36 publications

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the 6A1 ↔ 2T2 Ground-State Transformation of the [FeN4O2]+ Chromophore

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the 6A1 ↔ 2T2 Ground-State Transformation of the [FeN4O2]+ Chromophore

Synthesis and spectroscopic characterization of asymmetric Schiff bases derived from 4′-formylbenzo-15-crown-5 containing recognition sites for alkali and transition metal guest cations

Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [FeIII(5‐X‐salMeen)2]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition

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Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the ⁶A₁ ↔ ²T₂ Ground-State Transformation of the [FeN₄O₂]⁺ Chromophore

Unusual Magneto‐Structural Features of the Halo‐Substituted Materials [Fe^III(5‐X‐salMeen)₂]Y: a Cooperative [HS‐HS]↔[HS‐LS] Spin Transition