Moessbauer-Zeeman spectra of some octaethylporphyrinato- and tetraphenylporphinatoiron(III) complexes

Dolphin, David; Sams, J. R.; Tsin, Tsang Bik; Wong, Kit L. Tang

doi:10.1021/ja00474a011

Cited by 32 publications

(15 citation statements)

References 12 publications

(17 reference statements)

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“…2) in the starting structure prevented them from forming an intramolecular hydrogen bond during optimization. Although experimental measurements indicate a sextet ground state for the halide complexes, [60][61][62][63][64] predicted quartet state energies lie close to or slightly below the sextet energies, as found in previous calculations. [65][66][67] The energies listed in Table I include the zero-point energies α¯ω α /2 calculated from the predicted normal mode frequencies ω α , which favor the sextet state.…”

Section: Methodssupporting

confidence: 85%

“…88,89 Ferric porphyrin chlorides, in particular, have been cited as an illustration of this problem. 65 The ground state is experimentally established as a sextet, [60][61][62][63][64] but the lowest lying sextet and quartet states are predicted to lie close in energy. [65][66][67] Even after correcting for the larger zeropoint energy of the quartet state, our calculations predict comparable energies for the quartet and sextet states in all ferric porphyrin chlorides that we have considered (see Table I).…”

Section: A Electronic Statementioning

confidence: 99%

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Spectroscopic identification of reactive porphyrin motions

Barabanschikov

Demidov

Kubo

et al. 2011

The Journal of Chemical Physics

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Nuclear resonance vibrational spectroscopy (NRVS) reveals the vibrational dynamics of a Mössbauer probe nucleus. Here, 57 Fe NRVS measurements yield the complete spectrum of Fe vibrations in halide complexes of iron porphyrins. Iron porphine serves as a useful symmetric model for the more complex spectrum of asymmetric heme molecules that contribute to numerous essential biological processes. Quantitative comparison with the vibrational density of states (VDOS) predicted for the Fe atom by density functional theory calculations unambiguously identifies the correct sextet ground state in each case. These experimentally authenticated calculations then provide detailed normal mode descriptions for each observed vibration. All Fe-ligand vibrations are clearly identified despite the high symmetry of the Fe environment. Low frequency molecular distortions and acoustic lattice modes also contribute to the experimental signal. Correlation matrices compare vibrations between different molecules and yield a detailed picture of how heme vibrations evolve in response to (a) halide binding and (b) asymmetric placement of porphyrin side chains. The side chains strongly influence the energetics of heme doming motions that control Fe reactivity, which are easily observed in the experimental signal.

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Section: Methodssupporting

confidence: 85%

Section: A Electronic Statementioning

confidence: 99%

Spectroscopic identification of reactive porphyrin motions

Barabanschikov

Demidov

Kubo

et al. 2011

The Journal of Chemical Physics

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“…It has been suggested that the difference in the porphinato core size among P, Pz's, and Pc's is related to the various spin states of their chloroiron(III) complexes 15. For example, FeTPP(Cl) (chloroiron tetraphenylporphyrin) and FeOEP(Cl) (chloroiron octaethylporphyrin) are believed to be high‐spin (S = 5/2) systems,45, 46 while FeOEPz(Cl) manifests properties of an intermediate‐spin (S = 3/2) state 15. FePc(Cl) was reported to be intermediate spin or spin‐admixed (S = 3/2–5/2) 47.…”

Section: Resultsmentioning

confidence: 99%

“…The INDO‐SCF/CI calculations by Edwards et al49 predicted the 4 A 2 state to be about 0.22 eV lower than 6 A 1 (at the experimental geometry), similar to our result. Because the compounds that have been used in experiments15, 45, 46 contain organic substituents such as phenyl or ethyl, FeOEP(Cl) is also considered so as to examine the effect of the peripheral substituents. The calculated values (presented in parentheses in Table 4) show that these ethyl groups reduce the relative energy of 6 A 1 by about 0.1 eV, but the 4 A 2 state remains 0.2 eV lower than 6 A 1 .…”

Section: Resultsmentioning

confidence: 99%

Comparative study of metal‐porphyrins, ‐porphyrazines, and ‐phthalocyanines

2002

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A theoretical comparative study of complexes of porphyrin (P), porphyrazine (Pz), and phthalocyanine (Pc) with metal (M) = Fe, Co, Ni, Cu, and Zn has been carried out using a DFT method. The calculations provide a clear elucidation of the ground states for the MP/Pz/Pc molecules and for a series of [MP/Pz/Pc](x-) and [MP/Pz/Pc](y+) ions (x = 1, 2, 3, 4; y = 1, 2). There are significant differences among MP, MPz, and MPc in the electronic structure and other calculated properties. For FeP/Pz and CoP/Pz, the first oxidation occurs at the central metal, while it is the macroring of FePc and CoPc that is the site of oxidation. The smaller coordination cavity results in a stronger ligand field in Pz than in P. However, the benzo annulation produces a surprisingly strong destabilizing effect on the metal-macrocycle bonding. The effects of Cl axial bonding upon the electronic structures of the iron(III) complexes of P, Pz, and Pc were examined, as was the bonding of pyridine (py) to NiP, NiPz, and NiPc. The porphinato core size plays a crucial role in controlling the spin state of Fe(III) in these complexes. FePc(Cl) is predicted to be a pure intermediate-spin system, whereas NiPz(py)(2) and NiPc(py)(2) are metastable in high-spin (S = 1) states. The NiPz/Pc-(py)(2) binding energy curve has only a shallow well that facilitates decomposition of the complex. The NiP-(py)(2) bond energy is small, but the relatively deep well in the binding energy curve ought to make this system stable to decomposition.

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“…The upper temperature for the measurements on these samples (118 K) was limited by the softening temperature (ϳ120 K) of the toluene glass (48). It is assumed that D for FeTTPX, X ϭ F, Cl, Br, is approximately the same as for the analogous TPP complex and thus is in the range of 4 to 12.5 cm Ϫ1 (15,(33)(34)(35)(36)(37)(38). Over the temperature interval for which data were available, the temperature dependence of 1/T 1 for FeTTPX could be fitted using only the Orbach process with excited states at 2D and 6D (Table 1).…”

Section: Resultsmentioning

confidence: 99%