Why Does the Middle Band in the Absorption Spectrum of Ni(H2O)6 2+ Have Two Maxima?

Triest, Myriam; Bussière, Guillaume; Bélisle, Hugo; Reber, Christian

doi:10.1021/ed077p670.2

Cited by 26 publications

(19 citation statements)

References 1 publication

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“…Moreover, the stability constants collected for Fe II and Zn II (Table S12) are a strong support for assuming that the closely related homoleptic pseudo‐octahedral [Ni( L k ) 3 ] 2+ complexes (existing as mixtures of mer / fac isomers) are quantitatively formed in acetonitrile at 0.1 m , where well‐resolved absorption spectra can be recorded for the Ni( 3 T 2g ← 3 A 2g ), Ni( 3 T 1g ← 3 A 2g ) and Ni( 1 E g ← 3 A 2g ) d–d transitions (the symmetry labels assume O h symmetry, Figure S18). Non‐linear least‐squares fits of the experimental energies at the maximum of the absorption bands (Table S14) with the ligand‐field Equations pertinent to octahedral d 8 systems give the ligand‐field strengths Δ oct and Racah parameters B and C collected in Table .

true E ((), ^{3} A_{2 normalg}) = 0

true E ((), ^{1} E_{g}) = 8 B + 2 C - \frac{6 B^{2}}{Δ_{oct}}

true E ((), ^{3} T_{2 normalg}) = Δ_{oct}

true E ((), ^{3} T_{1 normalg}) = 1 . 5 Δ_{oct} + 7 . 5 B - 0 . 5 \sqrt{225 B^{2} + Δ_{oct}^{2} - 18 Δ_{oct} B}

…”

Section: Resultssupporting

confidence: 86%

Deciphering the Influence of Meridional versus Facial Isomers in Spin Crossover Complexes

Lathion

Guénée

Besnard

et al. 2018

Chemistry A European J

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Chelate coordination of non-symmetrical didentate pyrazine-benzimidazole (L1) or pyridine-benzimidazole (L2) N-donor ligands around divalent iron in acetonitrile produces stable homoleptic triple-helical spin crossover [Fe(Lk) ] complexes existing as mixtures of meridional (C -symmetry) and facial (C -symmetry) isomers in slow exchange on the NMR timescale. The speciation deviates from the expected statistical ratio mer/fac=3:1, a trend assigned to the thermodynamic trans-influence, combined with solvation effects. Consequently, the observed spin state Fe ↔Fe equilibria occurring in [Fe(Lk) ] refer to mixtures of complexes in solution, an issue usually not considered in this field, but which limits rational structure-properties correlations. Taking advantage of the selective and quantitative formation of isostructural facial isomers in non-constrained related spin crossover d-f helicates (HHH)-[LnFe(Lk) ] (Ln is a trivalent lanthanide, Lk=L5, L6), we propose a novel strategy for assigning pertinent thermodynamic driving forces to each spin crossover triple-helical isomer. The different enthalpic contributions to the spin state equilibrium found in mer-[Fe(Lk) ] and fac-[Fe(Lk) ] reflect the Fe-N bond strengths dictated by the trans-influence, whereas a concomitant solvent-based entropic contribution reinforces the latter effect and results in systematic shifts of the spin crossover transitions toward higher temperature in the facial isomers.

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true E ((), ^{3} A_{2 normalg}) = 0

true E ((), ^{1} E_{g}) = 8 B + 2 C - \frac{6 B^{2}}{Δ_{oct}}

true E ((), ^{3} T_{2 normalg}) = Δ_{oct}

true E ((), ^{3} T_{1 normalg}) = 1 . 5 Δ_{oct} + 7 . 5 B - 0 . 5 \sqrt{225 B^{2} + Δ_{oct}^{2} - 18 Δ_{oct} B}

…”

Section: Resultssupporting

confidence: 86%

Deciphering the Influence of Meridional versus Facial Isomers in Spin Crossover Complexes

Lathion

Guénée

Besnard

et al. 2018

Chemistry A European J

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“…After addition of Ni(II), both NTA-functionalized polymers showed nearly identical electronic spectra with absorption bands at λ 1 ) 622 nm and λ 2 ) 390 nm, which are characteristic for hexacoordinated Ni(II). 39 The visible absorption band λ 1 attributed to the 3 A 2g f 3 T 1g (F) transition is clearly resolved, while λ 2 , which is attributed to the 3 A 2g f 3 T 1g (P) transition, is present only as a shoulder due to superposition of several high intensity CT and intraligand bands in the domain <420 nm. As previously shown, these bands are characteristic for the [Ni(NTA)(H 2 O) 2 ] -complex 40 and therefore indicate that the metal indeed binds to the NTA group of the copolymers.…”

Section: Resultsmentioning

confidence: 91%

“…To determine the dissociation constant, K D , of the His-tag/ Ni 2+ -NTA interaction at the vesicle surface, we titrated His 10 -MBP-FITC and His 6 -EGFP, respectively, with increasing concentrations of Ni 2+ -doped-vesicles (PB 39 PEO 36 -SA-TrisNTA-Ni 2+ (10:1) vesicles), the content of Ni 2+ varying from 0.5 to 16 µM. To avoid errors due to the loss of the modified polymers during the preparation procedure (e.g., adsorption to the filter in the extrusion step), we determined the concentration of the Ni 2+ -NTA groups in the vesicle dispersions by inductive coupled plasma (ICP) atom emission spectroscopy.…”

Section: Resultsmentioning

confidence: 99%

Amphiphilic Diblock Copolymers for Molecular Recognition: Metal−Nitrilotriacetic Acid Functionalized Vesicles

et al. 2008

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Here we describe the design, synthesis, and characterization of new, metal-functionalized, amphiphilic diblock copolymers for molecular recognition. Polybutadiene-block-polyethylenoxide copolymers were synthesized by living anionic polymerization and end group functionalized with nitrilotriacetic acid and tris(nitrilotriacetic acid). After complexation with nickel and copper, these groups are known to selectively bind to oligohistidine residues of proteins. The polymers were characterized by 1H NMR spectroscopy, size exclusion chromatography, electron paramagnetic resonance, and UV-vis spectroscopy. Mixtures of these polymers with the respective nonfunctionalized block copolymers self-assemble in aqueous solution into vesicular structures with a controlled density of the metal complex end-groups on their surface. The accessibility of these binding sites was tested using maltose binding protein carrying a terminal decahistidine moiety and His-tagged enhanced green fluorescent protein as model systems. Fluorescence correlation spectroscopy clearly showed a significant and selective binding of these proteins to the vesicle surface.

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“…All calculated values for 10Dq and B are summarized in Table 1. The 10Dq/B ratios of 11–15 for 1 to 4 are higher than for homoleptic complexes with oxygen ligator atoms, illustrated by [Ni(H 2 O) 6 ] 2+ at a 10Dq/B ratio of 9.2 (16) in Fig. 2, and lower than the ratio of 18 for complexes with strong‐field ligands such as [Ni( o ‐phenanthroline) 3 ] 2+ (13–15), also included on the abscissa of Fig.…”

Section: Spectroscopic Resultsmentioning

confidence: 98%

Allowed and Forbidden d-d Transitions in Poly(3,5-dimethylpyrazolyl)methane Complexes of Nickel(II)†

Nolet¹,

Michaud²,

Bain³

et al. 2006

Photochem Photobiol

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Absorption spectra of four nickel(II) complexes with poly (pyrazolyl)methane ligands are presented in the NIR-VIS-UV region and the band system corresponding to the lowestenergy spin-allowed and spin-forbidden transitions is analyzed. A quantitative theoretical model involving coupled electronic states provides precise energies for the lowestenergy triplet and singlet excited states and allows comparisons between complexes with a variable number of nitrogen and oxygen ligator atoms. Singlet energies between 12 840 and 13 000 cm 21 are determined for heteroleptic complexes. These energies are in an intermediate range between those for homoleptic complexes with either nitrogen or oxygen ligator atoms with singlet states at approximately 12 000 and 14 000 cm 21, respectively. The new theoretical approach is compared to the traditional ligand-field parameters obtained from the maxima of the broad, spin-allowed absorption bands.

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Why Does the Middle Band in the Absorption Spectrum of Ni(H2O)6 2+ Have Two Maxima?

Cited by 26 publications

References 1 publication

Deciphering the Influence of Meridional versus Facial Isomers in Spin Crossover Complexes

Deciphering the Influence of Meridional versus Facial Isomers in Spin Crossover Complexes

Amphiphilic Diblock Copolymers for Molecular Recognition: Metal−Nitrilotriacetic Acid Functionalized Vesicles

Allowed and Forbidden d-d Transitions in Poly(3,5-dimethylpyrazolyl)methane Complexes of Nickel(II)†

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