NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities.

NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Research Abstract Details 

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NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Abstract Text:

Sheng Cai,Tatjana Kh Shokhireva,Dennis L Lichtenberger,F Ann Walker,

The NMR and EPR spectra of two bisimidazole and three bispyridine complexes of tetraphenylchlorinatoiron(III), [(TPC)Fe(L)2]+ (L = Im-d4, 2-MeHIm, 4-Me2NPy, Py, and 4-CNPy), have been investigated. The full resonance assignments of the [(TPC)Fe(L)2]+ complexes of this study have been made from correlation spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY) experiments and Amsterdam density functional (ADF) calculations. Unlike the [(OEC)Fe(L)2]+ complexes reported previously (Cai, S.; Lichtenberger, D. L.; Walker, F. A. Inorg. Chem. 2005, 44, 1890-1903), the NMR data for the [(TPC)Fe(L)2]+ complexes of this study indicate that the ground state is S = 1/2 for each bisligand complex, whereas a higher spin state was present at NMR temperatures for the Py and 4-CNPy complexes of (OEC)Fe(III). The pyrrole-8,17 and pyrroline-H of all [TPCFe(L)2]+ show large magnitude chemical shifts (hence indicating large spin density on the adjacent carbons that are part of the pi system), while pyrrole-12,13-CH2 and -7,18-CH2 protons show much smaller chemical shifts, as predicted by the spin densities obtained from ADF calculations. The magnitude of the chemical shifts decreases with decreasing donor ability of the substituted pyridine ligands, with the nonhindered imidazole ligand having slightly larger magnitude chemical shifts than the most basic pyridine, even though its basicity is significantly lower (4-Me2NPyH+ pKa = 9.7, H2Im+ pKa = 6.65 (adjusted for the statistical factor of 2 protons)). The temperature dependence of the chemical shifts of all but the 4-Me2NPy bisligand complexes studied over the temperature range of the NMR investigations shows that they have mixed (dxy)2(dxz,dyz)3/(dxzdyz)4(dxy)1 electron configurations that cannot be resolved by temperature-dependent fitting of the proton chemical shifts, with an S = 3/2 excited state in each case that in most cases lies at more than kT at room temperature above the ground state. The observed pattern of chemical shifts of the 4-CNPy complex and analysis of the temperature dependence indicate that it has a pure (dxzdyz)4(dxy)1 ground state and that it is ruffled, because ruffling mixes the a(2u)(pi)-like orbital of the chlorin into the singly occupied molecular orbital (SOMO). This mixing accounts for the negative chemical shift of the pyrroline-H (-6.5 ppm at -40 degrees C) and thus the negative spin density at the pyrroline-alpha-carbons, but the mixing is not to the same extent as observed for [(TPC)Fe(t-BuNC)2]+, whose pyrroline-H chemical shift is -36 ppm at 25 degrees C (Simonneaux, G.; Kobeissi, M. J. Chem. Soc., Dalton Trans. 2001, 1587-1592). Peak assignments for high-spin (TPC)FeCl have been made by saturation transfer techniques that depend on chemical exchange between this complex and its bis-4-Me2NPy adduct.

NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Publishing Authors By Initials

S Cai,TKh Shokhireva,DL Lichtenberger,FA Walker,

For similar environment and public health: environment: environment, controlled: temperature research abstracts see: environment and public health: environment: environment, controlled: temperature research

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NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Journal Published:

PUBLICATION TYPE: Research Support, U.S. Gov't,

Journal: Inorganic chemistry

VOLUME: 45

Page Numbers: 3519-31

Journal Abbreviation:

ISSN: 0020-1669

DAY: 1

MONTH: May

YEAR: 2006

NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Information

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LANGUAGE: eng

NlmUniqueID: 366543

NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Keywords Mesh Terms:

KEYWORDS: Temperature

MESH TERMS: chemistry

Chemical & Substance for Abstract: NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities. Information

Substance Name: chlorin

Registry Number: 2683-84-3

Grant and Affiliation Information for NMR and EPR studies of chloroiron(III) tetraphenyl-chlorin and its complexes with imidazoles and pyridines of widely differing basicities.

AFFILIATION: Department of Chemistry, University of Arizona, Tucson, Arizona 85721-0041, USA.

Country: United States

AGENCY: United States NIDDK

GRANT: DK-31038

ACRONYM: DK

MEDLINETA: Inorg Chem

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