<sup>14</sup>N,<sup>1</sup>H, and metal ENDOR of single crystal Ag(II)(TPP) and Cu(II)(TPP)

Brown, Theodore G.; Hoffman, Brian M.

doi:10.1080/00268978000100911

Cited by 129 publications

(82 citation statements)

References 34 publications

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“…48,49 In the case of Cu II , hyperfine coupling at g || (A || ) is also often observed and the correlation of g || and A || can provide qualitative information on the donor atoms in the inner coordination sphere of Cu II , as shown by Blumberg and Peisach, 50 as well as quantitative information on spin distribution, as shown e.g., by Brown and Hoffman for CuTPP (TPP = dianion of 5,10,15,20-tetraphenylporphine), which also involved the precise measurement of porphryin 1 H and 14 N hyperfine coupling by ENDOR. 51,52 For illustration, we show in Figure 1 Brown and Hoffman 51 ) to the equatorial d x2-y2 1 spin. Equations 1 are quite useful for the commonly found tetragonal geometry, but for other coordination environments, it is useful to employ a full matrix treatment with a strong-field representation and specific orbital energy levels or with a weak-field basis set and the AOM.…”

Section: Resultsmentioning

confidence: 99%

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

Telser¹

2006

J. Braz. Chem. Soc.

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Este artigo descreve de maneira um tanto pessoal, o uso da espectroscopia de ressonância paramagnética eletrônica (EPR), incluindo EPR de alta freqüência e alto campo (HFEPR) para investigar a estrutura eletrônica de complexos de íons de metal de transição. Os parâmetros Hamiltonianos de spin, obtidos a partir de experimentos EPR, matriz g para sistemas com S =1/2 e matrizes g e D (zero-field splitting) para sistemas com S > 1/2 fornecem informações sobre os níveis de energia dos orbitais d. Esta informação pode ser combinada com a teoria do campo ligante (TCL) para fornecer informações a respeito da estrutura eletrônica global de complexos paramagnéticos de metal de transição. Como tem sido discutido por outros autores a TCL ainda se mostra útil para o entendimento quantitativo destes complexos, mesmo com a atual disponibilidade de métodos computacionais avançados, como a teoria do funcional de densidade (DFT). A discussão é ilustrada por exemplos ao longo da série de transição, com configurações d n . This paper describes in a somewhat personal way an overview of the use of electron paramagnetic resonance (EPR) spectroscopy, including high-frequency and -field EPR (HFEPR) to unravel the electronic structure of transition metal ion complexes. The spin Hamiltonian parameters obtained from EPR experiments, namely the g matrix for systems with S =1/2 and the g and D (zero-field splitting) matrices for systems with S > 1/2 provide information on d orbital energy levels. This information can be combined with ligand-field theory (LFT) to provide information on the overall electronic structure of the paramagnetic transition metal complex. As has been discussed by others, LFT is still useful in providing such a quantitative understanding of these complexes, even in the day of advanced computational methods, such as density functional theory (DFT). The discussion is illustrated by examples across the d n configuration.

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Section: Resultsmentioning

confidence: 99%

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

Telser¹

2006

J. Braz. Chem. Soc.

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“…The 14 N signals in the CW EPR and Q-band ENDOR spectra were then simulated with this constraint to give the best fit to the data, which resulted in the hyperfine and nuclear quadrupole parameters given in Table 2. To reduce the number of fitted parameters, the Euler angles were fixed in line with single-crystal metalloporphyrin studies [51] where the axis of the largest principal hyperfine and nuclear quadrupole value point at the nickel ion [52]. Given the large number of adjustable parameters (five coupling parameters for each nitrogen), the error in the parameters is comparable to the relatively small difference between the nitrogen couplings, in particular in the g 1 -g 2 plane.…”

Section: Hydropyrrolic Nitrogens Of F 430mentioning

confidence: 99%

Coordination and binding geometry of methyl-coenzyme M in the red1m state of methyl-coenzyme M reductase

et al. 2008

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Methane formation in methanogenic Archaea is catalyzed by methyl-coenzyme M reductase (MCR) and takes place via the reduction of methyl-coenzyme M (CH 3 -S-CoM) with coenzyme B (HS-CoB) to methane and the heterodisulfide CoM-S-S-CoB. MCR harbors the nickel porphyrinoid coenzyme F 430 as a prosthetic group, which has to be in the Ni(I) oxidation state for the enzyme to be active. To date no intermediates in the catalytic cycle of MCR red1 (red for reduced Ni) have been identified. Here, we report a detailed characterization of MCR red1m (''m'' for methyl-coenzyme M), which is the complex of MCR red1a (''a'' for absence of substrate) with CH 3 -S-CoM. Using continuous-wave and pulse electron paramagnetic resonance spectroscopy in combination with selective isotope labeling ( 13 C and 2 H) of CH 3 -S-CoM, it is shown that CH 3 -S-CoM binds in the active site of MCR such that its thioether sulfur is weakly coordinated to the Ni(I) of F 430 . The complex is stable until the addition of the second substrate, HS-CoB. Results from EPR spectroscopy, along with quantum mechanical calculations, are used to characterize the electronic and geometric structure of this complex, which can be regarded as the first intermediate in the catalytic mechanism.

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“…In this respect Electronic Spin-Resonance (ESR) spectroscopy yields unique information about the nature of open-shell ground state and its dependence on the chemical environment. ESR spectra of Co(II) tetraphenyl porphyrine in matrices have been reported by Van Doorslaer and Schweiger [10] and by Brown and Hoffman for the analogous Cu(II) compound [11].…”

Section: Introductionmentioning

confidence: 99%

A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins

Atanasov

Daul

Rohmer

et al. 2006

Chemical Physics Letters

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. dedicate this work to the memory of late Prof. A. Schweiger. AbstractUsing a DFT based Ligand Field treatment (LFDFT) of the electronic structure of Co(II) and Cu(II) porphyrins (CoP and CuP) we analyse the origin of their EPR spectra. From a comparison between theoretical result on Co model clusters (CoP and CoP-ZnP dimer) we conclude that the g-tensor values are very sensitive to the axial coordination which stabilizes a 2 A 1 ground state in good agreement with experimental data. In contrast, DFT overestimates Cu-ligand covalency, leading to large discrepancy with experiments, and hence the orbital contribution to the computed g-values is too small. Using a numerical adjustment of nuclear charge for Cu, a good agreement between the computed and the experimental g-tensor values is observed. The influence of the DFT functional on the calculated g-tensor is also discussed.

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¹⁴N,¹H, and metal ENDOR of single crystal Ag(II)(TPP) and Cu(II)(TPP)

Cited by 129 publications

References 34 publications

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

Coordination and binding geometry of methyl-coenzyme M in the red1m state of methyl-coenzyme M reductase

A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins

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14N,1H, and metal ENDOR of single crystal Ag(II)(TPP) and Cu(II)(TPP)

Cited by 129 publications

References 34 publications

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

A perspective on applications of ligand-field analysis: inspiration from electron paramagnetic resonance spectroscopy of coordination complexes of transition metal ions

Coordination and binding geometry of methyl-coenzyme M in the red1m state of methyl-coenzyme M reductase

A DFT based ligand field study of the EPR spectra of Co(II) and Cu(II) porphyrins

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¹⁴N,¹H, and metal ENDOR of single crystal Ag(II)(TPP) and Cu(II)(TPP)