Resonance Raman detection of iron-ligand vibrations in cyano(pyridine)(octaethylporphinato)iron(III): Effects of pyridine basicity on the Fe-CN bond strength

Journal Article · Wed Sep 07 04:00:00 EDT 1988 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00291a035· OSTI ID:5775862

Uno, Tadayuki; Hatano, Keiichiro; Nishimura, Yoshifumi; Arata, Yoji

The influence of axial ligand basicity on the bonding of iron(III) in cyano adducts of octaethylporphyrin has been studied by resonance Raman spectroscopy. In a six-coordinate ferric low-spin complex, cyano(pyridine)(octaethylporphinato)iron(III), Fe(OEP)(CN)(py), Raman lines at 449 and 191 cm/sup /minus/1/ were assigned to the /nu/(Fe-CN) and /nu/(Fe-py) stretching modes, respectively. When pyridine was displaced with its derivatives, py-X, where X = 4-cyano, 3-acetyl, 3-methyl, 4-methyl, 3,4-dimethyl, and 4-dimethylamino, the /nu/(Fe-CN) stretching frequency was found to decrease in the complex with a high pyridine basicity. It was concluded that the stronger the trans pyridine basicity, the weaker the iron-carbon (cyanide) bond. A clear frequency shift was observed in the /nu//sub 4/ model, though most of the porphyrin vibrations were insensitive to the ligand substitution. The frequency of the /nu//sub 4/ mode, which is the C/sub a/-N(pyrrole) breathing vibration of the porphyrin skeleton, was found to increase with an increase in pyridine basicity. This is contrary to what was found in ferrous low-spin hemes as CO complexes. The /nu//sub 4/ shift in the CN complexes was explained in terms of forward /pi/ donation; donation of electrons from the porphyrin /pi/ orbital to the d/sub /pi// vacancy of the low-spin iron(III) weakened the C/sub a/-N(pyrrole) bonds and hence decreased the /nu//sub 4/ frequency. 32 references, 8 figures.

• Research Organization: Nagoya City Univ. (Japan)
• OSTI ID: 5775862
• Journal Information: Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 27:18; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
AZINES
CARBON 13
CARBON ISOTOPES
CARBOXYLIC ACIDS
COMPLEXES
CYANIDES
DATA
ELECTRONIC STRUCTURE
EVEN-ODD NUCLEI
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
IRON COMPLEXES
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
PYRIDINES
RAMAN SPECTRA
SPECTRA
STABLE ISOTOPES
TRACER TECHNIQUES
TRANSITION ELEMENT COMPLEXES