Unusual orientation of axial ligands in metalloporphyrins. Molecular structure of low-spin bis(2-methylimidazole)(meso-tetraphenylporphinato)iron(III) perchlorate

Scheidt, W. Robert; Kirner, J. F.; Hoard, J. L.; Reed, Christopher A.

doi:10.1021/ja00241a011

Cited by 102 publications

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“…The crystal field parameters V/ξ and Δ/ξ are then calculated from the g –tensor values according to Eq. (5) and (6):

\frac{V}{ξ} = \frac{E_{y z}}{ξ} - \frac{E_{x z}}{ξ} = \frac{g_{x}}{g_{z} + g_{y}} + \frac{g_{y}}{g_{z} - g_{x}}

\frac{normalΔ}{ξ} = \frac{E_{y z}}{ξ} - \frac{E_{x y}}{ξ} - \frac{V}{2 ξ} = \frac{g_{x}}{g_{z} + g_{y}} + \frac{g_{z}}{g_{y} - g_{x}} - \frac{V}{2 ξ}

where V represents the energy difference between the d xz and d yz orbitals, Δ the difference between the d xy and the averaged energy of the d xz and d yz orbitals and ξ the spin orbit coupling constant (~ 400 cm −1 ) 25,26. The knowledge of all three g values is necessary in order to determine V/ξ and Δ/ξ .…”

Section: Ligand Field Anisotropy In Low–spin Heme Ironmentioning

confidence: 99%

Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis‐Histidine and histidine‐methionine axial iron coordination

et al. 2009

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Six-coordinated heme groups are involved in a large variety of electron transfer reactions because of their ability to exist in both the ferrous (Fe 2+ ) and ferric (Fe 3+ ) state without any large differences in structure. Our studies on hemes coordinated by two histidines (bis-His) and hemes coordinated by histidine and methionine (His-Met) will be reviewed. In both of these coordination environments, the heme core can exhibit ferric low spin EPR signals with large g max values (also called type I, highly anisotropic low spin, or highly axial low spin, HALS species) as well as rhombic EPR (type II) signals. In bis-His coordinated hemes rhombic and HALS envelopes are related to the orientation of the His groups with respect to each other such that (i) parallel His planes results in a rhombic signal and (ii) perpendicular His planes results in a HALS signal. Correlation between the structure of the heme and its ligands for heme with His-Met axial ligation and ligand-field parameters, as derived from a large series of cytochrome c variants, show, however, that for such a combination of axial ligandsthere is no clear-cut difference between the large g max and the "small g-anisotropy" cases as a result of the relative Met-His arrangements. Nonetheless, a new linear correlation links the average shift <δ> of the heme methyl groups with the g max values.

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“…The crystal field parameters V/ξ and Δ/ξ are then calculated from the g –tensor values according to Eq. (5) and (6):

\frac{V}{ξ} = \frac{E_{y z}}{ξ} - \frac{E_{x z}}{ξ} = \frac{g_{x}}{g_{z} + g_{y}} + \frac{g_{y}}{g_{z} - g_{x}}

\frac{normalΔ}{ξ} = \frac{E_{y z}}{ξ} - \frac{E_{x y}}{ξ} - \frac{V}{2 ξ} = \frac{g_{x}}{g_{z} + g_{y}} + \frac{g_{z}}{g_{y} - g_{x}} - \frac{V}{2 ξ}

Section: Ligand Field Anisotropy In Low–spin Heme Ironmentioning

confidence: 99%

Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis‐Histidine and histidine‐methionine axial iron coordination

et al. 2009

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“…The ligand 4-methylimidazole-5-carbaldehyde (4-Me-5-CHOIm, L) is a molecule of considerable interest as a potential bidentate N,O donor that can exist in two tautomeric forms (scheme 1), an N-H tautomer (1) and an N-H tautomer (2). Tautomeric equilibrium in the imidazole ring can lead to different modes of coordination of 4-Me-5-CHOIm to metal ions.…”

Section: Introductionmentioning

confidence: 99%

“…Tautomer 2 allows the formation of five-membered N,O chelate rings with metal ions. It is well known that imidazole-metal ion derivatives as model compounds of metallobiopolymers generally use the simple imidazole heterocycle to mimic local metal coordination sites [1][2][3][4]. It would be of interest to obtain a Cd(II) complex with the above-mentioned ligand to establish the coordination mode of 4-Me-5-CHOIm.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, X-ray structure and spectroscopic investigation of an eight-coordinate cadmium(II) complex

Barszcz¹,

Hodorowicz

Jabłońska-Wawrzycka

et al. 2005

Journal of Coordination Chemistry

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2005) Synthesis, X-ray structure and spectroscopic investigation of an eight-coordinate cadmium(Reaction of 4-methylimidazole-5-carbaldehyde (L) with cadmium(II) nitrate (M : L ¼ 1 : 2; EtOH) yields a novel eight-coordinate mononuclear complex, [CdL 2 (NO 3 ) 2 ]. X-ray structural analysis indicates that the Cd(II) ion possesses what can be described as a double coordination sphere. The inner coordination sphere is pseudo-tetrahedral and consists of four atoms, N(1), N(11), O(21) and O(42), with bond lengths ranging from 2.252(2) to 2.371(2) Å . The second or outer coordination sphere is composed of four oxygen donors, O(7), O(17), O(22) and O(41), with Cd-O distances of 2.543(2) to 2.756(2) Å . The atoms of the external coordination sphere form pyramids with the pseudo-tetrahedral faces of the inner coordination sphere. IR and Raman spectra confirm the stabilization of the N-H isomer of the ligand.

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“…Values observed were 3.00, 2.2, and 1.47 or 2.84, 2.32, and 1.59. The use of the sterically hindered ligand 2-methylimidzole in [Fe(TPP)2-MeHIm) 2 ] + leads to a structure in which the two ligands have a relative perpendicular axial ligand orientation and an unusual EPR spectrum with typically only one of the three rhombic values observed and that with a g-value > 3.4 [32,53]. This signal has been called various names, but I prefer the term "large g max ."…”

Section: Discussionmentioning

confidence: 99%

Explorations in metalloporphyrin stereochemistry, physical properties and beyond

Scheidt

2008

J. Porphyrins Phthalocyanines

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A review of selected portions of our work in the area of porphyrin structure and physical characterization is presented. Topics covered include early work on periodic trends in first row transtion metalloporphyrins, a survey of electronic structure of iron derivatives including spin-state trends, ligand orientation effects and the elucidtion of unusual low-spin states for iron(II). A discussion of the different tlypes of high-spin iron(II) complexes and the effects of hydrogen bonding is given. A survey of nitric oxide (NO) derivatives is presented as well as a brief introduction into the use of nuclear resonance vibrational spectroscopy for the study of iron porphyrins and heme proteins.

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Unusual orientation of axial ligands in metalloporphyrins. Molecular structure of low-spin bis(2-methylimidazole)(meso-tetraphenylporphinato)iron(III) perchlorate

Cited by 102 publications

References 0 publications

Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis‐Histidine and histidine‐methionine axial iron coordination

Review: Studies of ferric heme proteins with highly anisotropic/highly axial low spin (S = 1/2) electron paramagnetic resonance signals with bis‐Histidine and histidine‐methionine axial iron coordination

Synthesis, X-ray structure and spectroscopic investigation of an eight-coordinate cadmium(II) complex

Explorations in metalloporphyrin stereochemistry, physical properties and beyond

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