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

Journal Article · Thu Aug 27 04:00:00 EDT 1987 · J. Phys. Chem.; (United States)

DOI:https://doi.org/10.1021/j100302a013· OSTI ID:6091219

Mitchell, M L; Li, X Y; Kincaid, J R; Spiro, T G

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), Journal Name: J. Phys. Chem.; (United States) Vol. 91:18; ISSN JPCHA
• 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
ABSORPTION SPECTROSCOPY
AZOLES
CARBOXYLIC ACIDS
COMPLEXES
DATA
DEUTERIUM
ENERGY LEVELS
EVEN-EVEN NUCLEI
EXCITED STATES
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROGEN ISOTOPES
IMIDAZOLES
INELASTIC SCATTERING
INFORMATION
INFRARED SPECTRA
INTERMEDIATE MASS NUCLEI
IRON 54
IRON COMPLEXES
IRON ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
LASER SPECTROSCOPY
LIGHT NUCLEI
NITROGEN 15
NITROGEN ISOTOPES
NORMAL-MODE ANALYSIS
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
RAMAN SPECTROSCOPY
RESONANCE SCATTERING
SCATTERING
SPECTRA
SPECTRAL SHIFT
SPECTROSCOPY
STABLE ISOTOPES
STRUCTURAL CHEMICAL ANALYSIS
TRANSITION ELEMENT COMPLEXES
VIBRATIONAL STATES