Metalloporphyrin electronic structure

For a review of absorption and emission spectroscopy of porphyrins and metalloporphyrins, see Gouterman, M. Optical spectra and electronic structure of porphyrins and related rings. In The Porphyrins Dolphin, D., Ed., Academic Press New York 1978, Vol. Ill, pp 1-165. 

Additionally, the axial ligands influence the electronic structure of metalloporphyrins. It is known that axial ligation has a substantial influence on the redox (80,81) and photovoltaic (82) properties... 

Karlin, K. D. Zuberbuhler, A. D. Formation, structure, and reactivity of copper dioxygen complexes, Bioinorganic Catalysis , 2nd edn. (Revised and Expanded) Eds. Reedijk, J. Bouwman, E. Marcel Dekker New York, 1999, pp. 469-534. Fukuzumi, S. Imahori, H. Biomimetic electron-transfer chemistry of porphyrins and metalloporphyrins, Electron Transfer in Chemistry , Vol. 2 Ed. Balzani, V. Wiley-VCH Verlag GmbH Weinheim, 2001, pp. 927-975. 

A molecular orbital treatment of the valence electronic structure of porphyrins indicates that the HOMO are two n orbitals that are close in energy to each other, but well separated in energy from all other occnpied orbitals. The relative energy of these two orbitals is predicted to be dependent npon the snbstituents present. For metalloporphyrins, which are discussed in the next section, occupied metal orbitals may be in the same energy region as these ligand-based orbitals, and the specific metal or ancUhary... 

Stevens, E. D. Electronic structure of metalloporphyrins. 1. Experimental electron density distribution of (meso-tetraphenylporphinato)cobalt(II). J. Amer. Chem. Soc. 103, 5087-5095 (1981). 

Schmidt, P. C. Electronic Structure of Intermetallic B 32 Type Zintl Phases. Vol. 65, pp, 91-133. Schneider, W. Kinetics and Mechanism of Metalloporphyrin Formation. Vol. 23, pp. 123-166, Schubert, K. The Two-Correlations Model, a Valence Model for Metallic Phases. Vol. 33,... 

Woodward has pointed out that porphyrins contain pyrrole units that are on average one half of an electron away from a stable 6-ji-electron configuration [Woodward (214)]. From the presumed tendency to become aromatic pyrrole units one can deduce a metalloporphyrin resonance structure like (VIII), where the methine bridge carbons have lost n-... 

Knowledge of the electronic structure of metalloporphyrins is useful, because such compounds can serve as models for biological redox systems. In this context one may wish to know whether, during a redox process, the electron is transferred directly from the metal center or whether porphyrin ligands are also involved in the process. Further, an understanding of the influence of the oxidation state of the metal on the porphyrin ring s charge and reactivity is of interest. 

Porphyrins and metalloporphyrins have been studied extensively due to their importance in biology. The related phthalocyanine macrocycles are often considered for comparison to porphyrins and are also of interest because of their increased use in molecular electronic devices. Much attention has been given to electronic structure calculations on porphyrins and metalloporphyrins,and as discussed earlier, the quality of a computational method for describing the electronic wavefunction of any system can be judged by the method s ability to calculate accurate ionizations energies. 

Models for the Electronic Structure of Metalloporphyrins from High-Resolution X-ray Diffraction and Ab Initio Calculations... 

Let us discuss the details of electronic structure of REE (Yb, Er) metalloporphyrins - Yb(acac)TPPBrg Yb(acac)TPP Er(acac)TPP and pristine TPP, TPPBrg. 

We have examined the electronic structure of valence band of the pristine porphyrin and Yb metalloporphyrins using facility of Helmholtz-Zentrum Berlin synchrotron radiation source (the Russian-Germany beam-line at BESSY) in the photon energy range 100-1000 eV and Kratos AXIS Ultra DLD spectrometer (the photon energy 1486.69 eV, A1K mono). Typical spectra are presented in Figs. 10.22 and 10.24. 

Belogorokhov,A. I., Bozhko, S. I., Chaika,A. N., Ionov,A. M., Trophimov, S.A., Rumyantseva, V. D. Vyalikh> D- (2009). Electronic Structure and Self-assembling Processes in Platinum Metalloporphyrines Photoemission and AFM Studies Applied Physics A. Materials Science and Processing, 94, 473-476. 

The electronic structure of metalloporphyrins is similar to that of a metal surface in that the metal atom is supported by a buffering supply of delocalized electrons and the 3d-states are comparatively localized. Iron atoms chelated by porphyrins form the active sites of hemeproteins. The vibrational frequencies - vco and vpec of liganded CO, and the fer-ric/ferrous reduction potential, Eq, respond to the electronegativity of peripheral substituents of the heme (ironporphyrin) plane as well as to perturbations via the protein-porphyrin interface [4],... 

In this communication I will compare the electronic structures of metal surfaces with that of metalloporphyrins and discuss the possibility of isolate non-local electronic perturbations for CO terminally bound to metal surfaces from the vibrational spectra of carbonyl-hemes. 

Van Wart examined the detail of compound I formation by reactions of HRP and a series of peroxides. In the course of the work, he found intermediate formation and proposed it being Fe(III) porphyrin dication [99]. Though electronic structure of the dication in biological system is not clear, the corresponding model complexes, Fe (TMP) dication and Fe (TDCPP) dication (TDCPP tetrakis(2,6-dichlorophenyl)-porphyrin), have been prepared in toluene [97, 98, 100]. The model complexes exhibit a blue shifted broad Soret band without showing any appreciable absorption in the region of 500 to 700 nm. These spectroscopic features of the Fe(III) porphyrin dications are common to other metalloporphyrin dications [101, 102] According to NMR and EPR... 

---