Spin Delocalization in Metallo-Pyrromethenes and Porphyrins

Eaton, D. R.; LaLancette, E. A.

doi:10.1063/1.1725763

Cited by 32 publications

(11 citation statements)

References 19 publications

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“…Nuclear magnetic resonance isotropic shifts arising from electron-nuclear hyperfine contact interactions have been employed to study paramagnetic Ni(I1) complexes with considerable success in recent years (1)(2)(3)(4)(5)(6). A typical example is the spin delocalization in the n-electron system of Ni(I1) complexes with aminotroponeimines (1)(2)(3), where the observations agreed very well with valence bond (VB) calculations.…”

Section: Introductionsupporting

confidence: 55%

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

Sun¹,

Grein²,

Brewer³

1972

Can. J. Chem.

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Relative p.m.r. isotropic shifts for the ligands in the complexes NiL,(NO,), (L = 4-picoline and 3,5-lutidine), NiL3(N03), (L = 3-picoline and 3,4-lutidine), and NiL,(NO,), (L = 2-picoline, 2,3-lutidine, 2,4-lutidine, and 2,5-lutidine) were determined in CDCI,. Proton hyperfine coupling constants for corresponding pyridine cations and analogous phenyl radicals were calculated by the INDO-MO method. Analysis of the p.m.r. shifts and subsequent correlation with the INDO data revealed that the spin transfer process between metal and ligand was dominated by a u-mechanism, as indicated by ring protons at the a-and B-positions. The y-ring proton and methyl protons at all positions indicated a n-mechanism was also operative through u-n spin polarization at the nitrogen atom. The INDO calculations based on spin densities of the hydrogen Is orbitals, however, predicted that all ring protons would be dominated by a u-mechanism, and that methyl protons at the a-and y-positions should manifest a n-mechanism. Both mechanisms should be operative for the 8-CH, protons, with 50-60% u-contribution in the pyridine cations and 30-50% u-contribution in the phenyl radicals. The pattern of spin polarization (i.e., negative at a-C and y-C, positive at P-C) is not altered by a small excess ofa or P spin in the n-system. However, the n-spin density ratios, especially at the a-and y-positions, areaffected, as is the magnitude of the n-spin densities on each carbon. A comparison of the observed isotropic shifts for the methyl protons and for the y-ring proton with the INDO calculated n-spin densities allows a determination of the spin delocalization in the ligand n-system. Les dCplacementsisotropiques relatifs p.m.r. pour les ligands dans les complexes NiL,(NO,), (L = picoline-4 et lutidine-3,5), NiL,(NO,), (L = picoline-3 et lutidine-3,4), et NiL,(NO,), (L = picoline-2,lutidine-2,3, lutidine-2,4 et lutidine-2,5), ont tte determines dans le CDCI,. Les constantes de couplage hyperfin du proton pour les cations pyridine correspondants et les radicaux analogues du phenyle, ont Cte calculees par la mtthode INDO-MO. L'analyse des deplacements p.m.r. et la correlation subsequente avec les donnees INDO, revhlent que le processus de transfert de spin entre le metal et le ligand est surtout un mecanisme-u, comme le montrent les protons du cycle en position a et P. Le proton y du cycle et les protons du methyle dans toutes les positions indiquent qu'un mecanisme-n est aussi effectif, par l'intermediaire d'une polarisation de spin u-n sur I'atome d'azote. Les calculs INDO, fondes sur les densites de spin dans les orbitales Is de I'hydroghne, laissent prevoir cependant que tous les protons du cycle seraient domines par un mkcanisme-u et que les protons du methyle sur les positions a et 7 manifesteraient un mecanisme de type n. Ces deux mecanismes seraient effectifs pour les protons du CH,-P, avec une contribution u de 50-60% dans les cations pyridine et 30-50% dans les radicaux phenyles. Le modele de la polarisation de spin (c'est-a-dire negative sur...

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Section: Introductionsupporting

confidence: 55%

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

Sun¹,

Grein²,

Brewer³

1972

Can. J. Chem.

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“…Recently, shifts to both high and low fields have been observed in a related compound, ferric tetraphenylporphyrin chloride, in CDCli solution (Eaton and LaLancette, 1964). This compound was found to be spin free, having 5 unpaired electrons.…”

Section: Discussionmentioning

confidence: 99%

Nuclear Magnetic Resonance Studies of Cytochrome c. Possible Electron Delocalization^*

Kowalsky¹

1965

Biochemistry

120

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“…Effects of paramagnetism on nuclear magnetic resonance spectra of nickel and other metal complexes have received considerable study (Eaton and Phillips, 1965). Eaton and LaLancette (1964) have discussed contact shifts observed with an iron(III) tetraphenylporphyrin in terms of spin delocalization from the metal ion into the porphyrin 7r-electron system. The contact shifts observed here with nickel porphyrins where meso and ß protons are shifted in opposite directions also suggest that the spin delocalization is taking place at least in part by a -delocalization mechanism.…”

Section: Discussionmentioning

confidence: 99%

Substituted deuteroporphyrins. V. Structures, stabilities, and properties of nickel(II) complexes with axial ligands

McLees¹,

Caughey²

1968

Biochemistry

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Spin Delocalization in Metallo-Pyrromethenes and Porphyrins

Abstract: Fermi contact shifts have been observed in the NMR spectra of Ni II and Co II pyrromethenes and of Fe III tetraphenylporphyrin chloride. These shifts have been interpreted in terms of delocalization of spin from the metal d orbitals to the lowest antibonding ligand π orbital.

Cited by 32 publications

References 19 publications

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

Nuclear Magnetic Resonance Studies of Cytochrome c. Possible Electron Delocalization^*

Substituted deuteroporphyrins. V. Structures, stabilities, and properties of nickel(II) complexes with axial ligands

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Spin Delocalization in Metallo-Pyrromethenes and Porphyrins

Abstract: Fermi contact shifts have been observed in the NMR spectra of Ni II and Co II pyrromethenes and of Fe III tetraphenylporphyrin chloride. These shifts have been interpreted in terms of delocalization of spin from the metal d orbitals to the lowest antibonding ligand π orbital.

Cited by 32 publications

References 19 publications

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

INDO–MO Calculations and Proton Isotropic Shifts of Methyl-Substituted Pyridine Ligands in Ni(II) Complexes

Nuclear Magnetic Resonance Studies of Cytochrome c. Possible Electron Delocalization*

Substituted deuteroporphyrins. V. Structures, stabilities, and properties of nickel(II) complexes with axial ligands

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Nuclear Magnetic Resonance Studies of Cytochrome c. Possible Electron Delocalization^*