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Electronic, Spectral, and Electrochemical Properties of (TPPBr(x)())Zn Where TPPBr(x)() Is the Dianion of beta-Brominated-Pyrrole Tetraphenylporphyrin and x Varies from 0 to 8

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dc.contributor Wichita State University. Department of Chemistry en_US
dc.contributor.author D'Souza, Francis en_US
dc.contributor.author Zandler, Melvin E. en_US
dc.contributor.author Tagliatesta, Pietro en_US
dc.contributor.author Ou, Zhongping en_US
dc.contributor.author Shao, Jianguo en_US
dc.contributor.author Van Caemelbecke, Eric en_US
dc.contributor.author Kadish, Karl M. en_US
dc.date.accessioned 2012-02-06T17:17:01Z
dc.date.available 2012-02-06T17:17:01Z
dc.date.issued 1998-09-07 en_US
dc.identifier 11670602 en_US
dc.identifier 0366543 en_US
dc.identifier ic980336y en_US
dc.identifier.citation Inorganic chemistry. 1998 Sep 7; 37(18): 4567-4572. en_US
dc.identifier.issn 1520-510X en_US
dc.identifier.issn 0020-1669 en_US
dc.identifier.uri http://hdl.handle.net/10057/4383
dc.description Full text of this article is not available in SOAR. en_US
dc.description.abstract The electronic, spectral, and electrochemical characterization of (meso-tetraphenylporphyrinato)zinc(II) complexes bearing between 0 and 8 bromo substituents at the beta-pyrrole positions is reported. The investigated compounds are represented as (TPPBr(x)())Zn where TPPBr(x)() is the dianion of brominated 5,10,15,20-tetraphenylporphyrin and x varies between 0 and 8. Each porphyrin undergoes four well-defined one-electron transfer reactions to yield porphyrin pi-cation radicals and dications upon oxidation and porphyrin pi-anion radicals and dianions upon reduction. Half-wave potentials for the first reduction of (TPPBr(x)())Zn can be described by a single linear free energy relationship, and plots of E(1/2) versus the number of Br groups on the complex show a linear correlation with a positive slope of 63 mV per Br group. This is not the case for the other three electron transfer processes of the compounds where plots of E(1/2) versus the number of Br groups show distinctly different linear correlations for derivatives with 0-4 Br groups and those with 4-8 Br groups. The effect of increasing number of Br groups on the spectral and electrochemical properties of the neutral complexes was examined over the whole series of compounds, and these experimental results are compared to results of theoretical calculations by semiempirical molecular orbital AM1 methods using configurational interactions (CI) over the four Gouterman frontier pi-orbitals. The dihedral angle containing the four porphyrin macrocycle ring nitrogens is proposed as a measure of porphyrin ring nonplanarity, and this value increases with increasing number of Br substituents on (TPPBr(x)())Zn. Results of the AM1-CI = 4 calculations indicate that the spectrally determined HOMO-LUMO gap, i.e., the energy corresponding to the low-energy absorption band, varies in a nonlinear fashion with increasing number of Br substituents on the macrocycle and this is due to both the electronic effect of the substituents and the macrocycle nonplanarity. The HOMO-LUMO gaps theoretically calculated by AM1-CI = 4 methods thus parallel values which are experimentally obtained by electrochemistry or spectroscopy. The lack of well-defined linear free energy relationships for all processes except for the first reduction can be explained on the basis of electronic effects caused by the halogen substituents and nonplanar macrocyclic distortions induced by steric interactions among the peripheral substituents. In the case of porphyrin dication formation, the redox potentials are virtually independent of the bromo substituents. en_US
dc.format.extent 4567-4572 en_US
dc.language.iso eng en_US
dc.publisher American Chemical Society en_US
dc.relation.ispartofseries Inorganic chemistry en_US
dc.relation.ispartofseries Inorg Chem en_US
dc.source NLM en_US
dc.title Electronic, Spectral, and Electrochemical Properties of (TPPBr(x)())Zn Where TPPBr(x)() Is the Dianion of beta-Brominated-Pyrrole Tetraphenylporphyrin and x Varies from 0 to 8 en_US
dc.type Article en_US
dc.description.version peer reviewed en_US
dc.rights.holder Copyright © 1998 American Chemical Society en_US

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