Axial ligand and out-of-plane vibrations for bis(imidazolyl)heme: Raman and infrared /sup 54/Fe, /sup 15/N, and /sup 2/H isotope shifts and normal coordinate calculations
Resonance Raman spectra of bis(imidazole) (ImH) complexes of Fe/sup II/ and Fe/sup III/ porphyrins reveal a band at approx.200 cm/sup -1/, assignable to the symmetric Fe-(ImH)/sub 2/ stretch via its 5-cm/sup -1/ downshift upon ImH-d/sub 4/ substitution. This band is enhanced in resonance with the Soret band for Fe/sup II/ porphyrins, suggesting direct coupling with the ..pi..-..pi.. state. For Fe/sup III/, this is observed only for protoporphyrin IX in aqueous solution, associated with aggregate formation. The low-frequency infrared spectrum of ((ImH)/sub 2/Fe/sup III/OEP)ClO/sub 4/ has been analyzed with the aid of /sup 54/Fe, /sup 15/N(pyrrole), meso-d/sub 4/, and ImH-d/sub 4/ isotope substitutions. The isotope shifts provide evidence that the Fe-(ImH)/sub 2/ antisymmetric stretch is essentially completely mixed between two modes, at 385 and 319 cm/sup -1/. This mixing is attributed to interaction between the axial ligand stretch and on out-of-plane pyrrole tilting mode. The mixing is confirmed by normal coordinate calculations of the out-of-plane modes, in which all of the isotope shifts are satisfactorily reproduced. The RR spectrum of ((ImH)/sub 2/Fe/sup III/OEP)/sup +/ is reexamined with the aid of RR difference spectroscopy, and the previously reported /sup 54/Fe sensitivity of bands at 256 and 361 cm/sup -1/ is shown to be in error. The 361-cm/sup -1/ band is assigned to the 2v/sub 35/ skeletal mode overtone, believed to be in Fermi resonance with the totally symmetric in-plane mode v/sub 8/ at 345 cm/sup -1/. The 256-cm/sup -1/ band, which disappears when the imidazole ligands are replaced by cyanide, may be an out-of-plane mode. Assignment of a band at 470 cm..sqrt../sub 1/, observed in bis-ligated iron OEP complexes, to an out-of-plane pyrrole folding mode is confirmed via a 2-cm/sup -1/ /sup 15/N(pyrrole) downshift.
- Research Organization:
- Princeton Univ., NJ
- OSTI ID:
- 6091219
- Journal Information:
- J. Phys. Chem.; (United States), Vol. 91:18
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
DEUTERIUM
ISOTOPE EFFECTS
IMIDAZOLES
VIBRATIONAL STATES
IRON 54
IRON COMPLEXES
NITROGEN 15
PORPHYRINS
ABSORPTION SPECTROSCOPY
EXPERIMENTAL DATA
INFRARED SPECTRA
NORMAL-MODE ANALYSIS
RAMAN SPECTROSCOPY
RESONANCE SCATTERING
SPECTRAL SHIFT
STRUCTURAL CHEMICAL ANALYSIS
AZOLES
CARBOXYLIC ACIDS
COMPLEXES
DATA
ENERGY LEVELS
EVEN-EVEN NUCLEI
EXCITED STATES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
INELASTIC SCATTERING
INFORMATION
INTERMEDIATE MASS NUCLEI
IRON ISOTOPES
ISOTOPES
LASER SPECTROSCOPY
LIGHT NUCLEI
NITROGEN ISOTOPES
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SCATTERING
SPECTRA
SPECTROSCOPY
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties
400202 - Isotope Effects
Isotope Exchange
& Isotope Separation