Porphyrins molecular structure

Hydrodemetallation pathways for Ni-etioporphyrin and Ni-tetra(3-methylphenyl)porphyrin are shown in Fig. 20. Both are characterized by a sequential hydrogenation-hydrogenolysis global mechanism, but important differences are apparent. Ware and Wei (1985a) rationalized the differences in porphyrin reactivity on the basis of porphyrin molecular structure. Structural differences on the periphery of the metalloporphyrin, in particular the substituent groups at the /3-pyrrolic and methine bridge... 

Scheldt WR, Lee YJ, Hatano K (1984) Preparation and structural characterization of nitrosyl complexes of ferric porphyrinates. Molecular structure of aquonitrosyl (meso-tetraphenyl-porphinato)iron (III) perchlorate and nitrosyl (octaethylporphinato)iron (III) perchlorate. J Am Chem Soc 106 3191-3198... 

An unusual porphyrin-supported hafnium guanidinate was obtained from the reaction of (TTP)Hf=NAr (TTP = meso-tetra-p-tolylporphyrinato dianion, Ar = 2.6-diisopropylphenyl) with 1,3-diisopropylcarbodiimide. The molecular structure of the product, (TTP)Hf[Pr NC(NPr )(NAr)] is shown in Figure 24. ° ... 

Fk . 7. Molecular structures of selected organomctallic rhodium and iridium porphyrin com-... 

Figure 13 Molecular structure of a co-facial zinc porphyrin dimer with a xanthene spacer.784...

J.R. Bolton In solution most photochemical electron transfer reactions occur from the triplet state because in the collision complex there is a spin inhibition for back electron transfer to the ground state of the dye. Electron transfer from the singlet excited state probably occurs in such systems but the back electron transfer is too effective to allow separation of the electron transfer products from the solvent cage. In our linked compound, the quinone cannot get as close to the porphyrin as in a collision complex, yet it is still close enough for electron transfer to occur from the excited singlet state of the porphyrin Now the back electron transfer is inhibited by the distance and molecular structure between the two ends. Our future work will focus on how to design the linking structure to obtain the most favourable operation as a molecular "photodiode . 

The out-of-plane orientation of chromophores can be more easily controlled in LB films as compared with the in-plane orientation. Many chromophores are known to show anisotropic orientation in the surface normal direction. The molecular structure of chromophores and their position in amphiphile molecules, the surface pressure, the subphase conditions are among those affect their out-of-plane orientation. The out-of-plane orientation has been studied by dichroic ratio at 45° incidence, absorbance ratio at normal and 45° incidence, and incident angle dependence of p-polarized absorption [3,4,27,33-41]. The evaluation of the out-of-plane orientation in LB films is given below using amphipathic porphyrin (AMP) as an example [5,10,12]. 

An important class of porphyrins is that constituted by confor-mationally distorted porphyrins, which mimic the non-planar geometry of the porphyrins present in photosynthetic systems.89 Obtainment of such non-planar distortions is associated with the introduction into the macrocyclic frame of proper crowding substituents, which therefore not only cause structural distortion but also affect, through their electronic effects, the redox potentials. A typical case is that constituted by [Cun(OETPP)] (OETPP = 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin), the saddle-distorted molecular structure of which is illustrated in Figure 56.102... 

The molecular structure of a Co(II) macrocycle complex that in some way mimics the strapped-type metal-porphyrin complexes is illustrated in Figure 13.18 19... 

Rg. 5. Molecular structures of selected Group 13 organometallic porphyrin complexes (a) AKOEPXCHs), (b) InfEtioPcXCeHslJ (c) Ga(TAP)(CH=CH2) (TAP = tetraanisylpor-... 

Fig. 7. Molecular structures of selected Group 15 organometallic porphyrin cations and complexes (a) [P(0EP)(C6H5)(0H)]PF6, (b) P(OEP)(C2H5)(=0), 5 [P(OETPP)(CH3)2]PF6, ...

Fig. 9. Molecular structures of selected metal—metal bonded main group porphyrin complexes (a) (OEP)InMn(CO)5, 54 (b) (OEP)SnFe(CO)4, (c) (TPP)SnMn(CO)4HgMn(CO)5. ...

Porphyrin and nonporphyrin metals associated with asphaltenes have not been easy to identify in terms of molecular structure. This is partly due to the fact that the characteristics (i.e., spectra) of all possible model nonporphyrin compounds have not been studied. Nonporphyrin metals are probably small polar molecules that precipitate as asphaltenes (Filby, 1975) or complex at defect sites in large aromatic sheet structures of the type shown in Fig. 10. Porphyrins with increased aromaticity and systems with low aromaticity due to discontinued ring conjugation are both characterized as nonporphyrin species. These compounds do not have the characteristic visible absorption spectra and hence are not readily identified. It is also possible that some of the porphyrin in the residuum may not be extracted and identified due to intermolecular association with the asphaltene-generating molecules. 

Fig. 7. A plot of the upheld ring current shifts measured in porphyrins, and in phtalo-cyanine model complexes where aliphatic hydrocarbons were attached to the central metal ion (Caughey and Ibers (18) Esposito et al. (30)). The positions of the observed protons were derived within the accuracy indicated by the ellipses from the known molecular structures. Z and r are the distances from the ring center perpendicular to the plane, and in the plane of the ring, respectively. The dashed line indicates the van der Waal thickness of the porphyrin ring. (Reproduced from ref. (99))...

As already mentioned, the coordination type of the Ru, Os, Rh and Ir porphyrins is C (Fig. 2), i.e. distorted octahedral about the metal which is in most cases a d6 system occasionally, d5, d4, or d2 systems are encountered. Table 2 gives a compilation of compounds the molecular structures of which have been determined by X-ray crystallography. The numbers of entries given for the individual noble metals approximately reflects the intensity of research done for the respective metal. For details and special structural aspects, the reader is referred to the original literature and a previous review by Scheidt and Lee [143]. Here, just a few general notes will be made. Phthalocyanine systems are not incorporated. 

FIGURE 7.26. (a) Molecular structure of compounds 42—45 (b) TEM images of a bundle of nanorods formed by compound 43 (Upper), and closer view of the bundle (Lower), (c) Pictorial representation of the nanorods formed by self-assembly of salt 43 in water, (d) Nanotubules formed by compound 45 observed at different scales. The measures of the two focused tubules are 35 x 530 and 50 x 470 nm. (e) Most stable dimeric structures of 45. Note that Upper is 6 kcal/mol per molecule more stable than Lower. (Upper) Interlayered structure (see text). (Lower) Porphyrin stacked structure. Notice that the porphyrin stacked structure is 2 kcal/mol per molecule more stable than the interlayered structure. 

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