/sup 59/Co NMR of cobalt(III) porphyrin complexes. 2. Electric field gradients, d-orbital populations, and hydrogen bonding
Journal Article
·
· J. Am. Chem. Soc.; (United States)
A series of six-coordinate cobalt(III) tetraphenylporphyrin complexes with para substituents on the phenyl groups and with a variety of axial imidazole ligands has been prepared. The /sup 59/Co NMR spectra of these complexes in a number of solvents and at several field strengths are reported. Shielding anisotropy is very small, confirming the authors earlier suggestion that porphyrin, imidazole, and ammonia ligands have nearly the same position in the spectrochemical series. The chemical shift /delta/ and line width /omega//sub 1/2/ increase as the para substituent on the TPP phenyl rings becomes electron-releasing. Correlations of /delta/ and /omega//sub 1/2/ with Hammett /sigma/ substituent constants are noted. A simple molecular orbital model is used to rationalize both chemical shift and line width changes. It is concluded that variations in /omega//sub 1/2/ with substituent arise from changes in the electric field gradient, q, which in turn depends on the extent of mixing of metal 3d and ligand /pi/ orbitals. The chemical shift and line width also depend on the substituent on the imidazole N-1 nitrogen. In particular, hydrogen bonding to solvent or added base from axial imidazoles containing N-H group strongly affects /omega//sub 1/2/, and the conclusion is reached that /sup 59/Co NMR is a good way to study such proximal hydrogen-bonding interactions. The /sup 59/Co NMR spectra are dominated by quadrupolar relaxation, and this is discussed along with other possible relaxation mechanisms. 61 references, 7 figures, 5 tables.
- Research Organization:
- Brown Univ., Providence, RI (USA)
- OSTI ID:
- 6048065
- Journal Information:
- J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 110:21; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
CARBOXYLIC ACIDS
CHEMICAL PREPARATION
COBALT 59
COBALT COMPLEXES
COBALT ISOTOPES
COMPLEXES
DATA
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
INTERMEDIATE MASS NUCLEI
ISOTOPES
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
SOLVENT PROPERTIES
SPECTRA
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
CARBOXYLIC ACIDS
CHEMICAL PREPARATION
COBALT 59
COBALT COMPLEXES
COBALT ISOTOPES
COMPLEXES
DATA
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
INTERMEDIATE MASS NUCLEI
ISOTOPES
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
SOLVENT PROPERTIES
SPECTRA
STABLE ISOTOPES
SYNTHESIS
TRANSITION ELEMENT COMPLEXES