Spin coupling in metalloporphyrin .pi.-cation radicals

Erler, Brian S.; Scholz, William F.; Lee, Young Ja; Scheidt, W. Robert; Reed, Christopher A.

doi:10.1021/ja00243a016

Cited by 100 publications

(77 citation statements)

References 2 publications

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“…2, i.e., the Cu-N(pyr), Cu-N(an)eq, and Cu-N(an)ax interactions with the N and R values of 1.6 and 2.05 Å, 2.4 and 1.98 Å, and 2.4 and 2.32 Å, respectively, where N(pyr), N(an)eq, and N(an)ax, respectively, denote the coordinating nitrogen atom of H2tpp, AN at the equatorial site, and AN at the axial site. Interestingly, the R value for Cu-N(pyr) in the Cu(II)-SAT complex (Cu(H2tpp)(an)4 2+ ) is larger than that (2.02 Å) of Cu(tpp), [71][72][73][74] while the R value of 1.98 Å for Cu-N(an)eq is alomost identical with that (1.99 Å) of the equatorial site of Cu(an)6 2+ . 75 The longer bond distance of Cu-N(pyr) rather than that of Cu(tpp), in which the Cu 2+ ion is just incorporated into the porphyrin core, is ascribed to the limitation due to the steric geometry of the porphyrin core.…”

Section: ·2 Structure Of Cu(ii)-sat Complex As Determined By Fluoresmentioning

confidence: 91%

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

2001

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The metalloporphyrin formation reaction is one of the important processes from both analytical and bioinorganic points of view.The large molar absorption coefficient and very high stability of the metalloporphyrins are very useful for the highly sensitive analysis of trace amounts of metal ions, and the size selectivity of the porphyrins is valuable for the separation of various kinds of metal ions. 1-7 A variety of metalloporphyrin formation rates are also applicable for the kinetic analysis of metal ions. We succeeded in the detection of the sitting-atop (SAT) copper(II) complex of TPP (5,10,15,20-tetraphenylporphyrin) in acetonitrile (AN) as a solvent with a very low Brønsted basicity, where two pyrrolenine nitrogens in the Cu(II)-SAT complex coordinate to the metal ion and two protons still remain on the pyrrole nitrogens. The structure parameters around the copper(II) ion in the Cu(II)-SAT complex, as determined by a fluorescent EXAFS method, suggest an axially elongated and equatorially distorted six-coordinate geometry. We measured the rates of the formation reaction of the SAT complexes for a series of transition metal(II) ions in AN using the stopped-flow technique. We propose the mechanism where there is a rapid deformation equilibrium of the porphyrin ring prior to the rate-determining step of the bond rupture of a coordinated solvent molecule on the metal(II) ion. Furthermore, we measured the rates of the deprotonation reaction of the Cu(II)-SAT complex by some Brønsted bases and indicated that the rate-determining step is the attack of the base on the proton of the pyrrole nitrogen in the SAT complex. Finally, a unified mechanism relevant to the porphyrin metalation mechanism has been proposed.

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Section: ·2 Structure Of Cu(ii)-sat Complex As Determined By Fluoresmentioning

confidence: 91%

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

2001

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“…Non-planar cores lead to antiferromagnetically coupled systems since only when the porphinato core deviates signi®cantly from D 4h symmetry are the metal d and ligand a 1u or a 2u orbitals not orthogonal and antiferromagnetic coupling can occur. The diamagnetism of [Cu(TPP á )] + [3,13] and the reduced moment of [Fe(TTP á )(Cl)] + [14], both consistent with antiferromagnetic coupling, were the ®rst derivatives that led to this correlation. Subsequently, the paramagnetism of the mononuclear derivative of [Cu(TMP á )] + [17] (planar core) and the diamagnetism of [Cu(OETPP á )] + [7] and [Cu(OETPP á )(Py)] + [8] (saddled cores) fully con®rmed the importance of core symmetry in controlling the nature of the spin coupling.…”

Section: Core Conformation Changes and Ring-ring Interactionsmentioning

confidence: 91%

Structural deformations and bond length alternation in porphyrin π-cation radicals

Scheidt

2001

J. Biol. Inorg. Chem.

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This review discusses the structural changes that occur when the porphyrin ring of metalloporphyrin complexes is oxidized to form a pi-cation radical species. Although various differences in core conformation between the pi-cation derivative and the unoxidized homologue have been observed, there does not appear to be a general pattern of change. A frequently observed feature in pi-cation derivatives is the appearance of an alternating bond distance pattern in the inner ring of the porphyrin consistent with a localized structure rather the delocalized structure usually seen. The pattern, first seen in cofacial dimeric structures, has now been seen in monomeric systems as well. The nature and frequency of the observation and possible explanation are given.

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“…Study of model Co II porphyrins with oxidation properties 4 have shown that depending on the oxidation conditions, an electron can be released from either the metal atom s or the porphyrin ring. 6 In sublimed layers of meso-tetraphenylporphyrinatocobalt(IO (CoTPP) under diminished pressure of NO 2, the metal is oxidized 7 in the first stage to form a five-coordinate extracomplex O2N 9 CoI[ITPP. This work is devoted to spectral studies of consecutive transformations in the sublimed CoTPP layer in the NO 2 atmosphere.…”

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confidence: 99%

Oxidation sequence of sublimedmeso-tetraphenylporphyrinatocobalt(II) films in an atmosphere of nitrogen dioxide

Kurtikyan

Stepanyan

1998

Russ Chem Bull

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Sublimed films of meso-tetraphenylporphyrinatocobalt(n) (CoTPP) undergo a series of chemical transformations in an atmosphere of NO 2. In the first stage, at low NO 2 pressures, the axial five-coordinate CoIIXTPP -NO 2 complex is formed. An increase in the NO 2 pressure and/or exposure results in subsequent oxidation with the formation of a 7t-radical cation CoTPP' +. In the latter, according to the IR spectral data, nitrogen dioxide is axially coordinated by the cobalt ion. Further increase in the NO2 pressure leads to both the formation of a dication and nitration of the porphyrin ring most likely at the meso-and 13-pyrrolic positions. Irreversible chemical transformations in the sublimed CoTPP films prevent their use as NO 2 sensors.Key words: meso-tetraphenylporphyrinatocobalt(tl), sublimed films, n-radical cations, IR and UV-VIS spectroscopy, nitrogen dioxide, nitration, isoporphyrin.Tetraarylporphyrins can form microporous "porphytin sponges," which allows incorporating guest molecules with different shapes and sizes. 1,2We have previously shown 3 that the structure of sublimed layers of meso-tetraphenylporphyrin (MTPP) metallocomplexes is also sponge-like. The microporosity of samples increases if the sublimed layers are formed during deposition on a low-temperature (T = 80 K) surface. In these layers, potential reagents can easily diffuse across the thickness, and the adducts that formed can be studied by spectral methods without interference by a solvent. Study of model Co II porphyrins with oxidation properties 4 have shown that depending on the oxidation conditions, an electron can be released from either the metal atom s or the porphyrin ring. 6 In sublimed layers of meso-tetraphenylporphyrinatocobalt(IO (CoTPP) under diminished pressure of NO 2, the metal is oxidized 7 in the first stage to form a five-coordinate extracomplex O2N 9 CoI[ITPP.This work is devoted to spectral studies of consecutive transformations in the sublimed CoTPP layer in the NO 2 atmosphere. ExperimentalSublimation was carried out in a vacuum cryostat with a KBr or CaF 2 support cooled with liquid nitrogen for recording IR and UV spectra, respectively. Then the sublimed layer was heated to 283 K under dynamic vacuum, and NO 2 was introduced in the cryostat. The pressure of NO 2 in the 4--40 Pa interval was monitored by a vacuum therrnocouple lamp. The CoTPP layer was exposed to the NO 2 atmosphere for a certain time, then the samples were exposed in high vacuum, and the IR or UV-VIS spectra were recorded. Taking into account potentialities of electron and IR-Fourier spectroscopy, we carried out some measurements in the NO 2 atmosphere, which made it possible to monitor the dynamics of the process.The synthesis and purification of NO 2 were described in Ref. 8.IR spectra in the 450--4000 cm -1 region were recorded on a Specord IR-75 spectrometer and a Perkin--Elmer I600 Fourier-spectrometer (the spectral width of the gap was 4 cm-t). UV-VIS spectra were recorded on Speeord M-40 and Beckman DU-640i spectrophotometers. Results and D...

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Spin coupling in metalloporphyrin .pi.-cation radicals

Cited by 100 publications

References 2 publications

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

Dynamic Study of Metal-Ion Incorporation into Porphyrins Based on the Dynamic Characterization of Metal Ions and on Sitting-Atop Complex Formation

Structural deformations and bond length alternation in porphyrin π-cation radicals

Oxidation sequence of sublimedmeso-tetraphenylporphyrinatocobalt(II) films in an atmosphere of nitrogen dioxide

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