Consistent porphyrin force field. 1. Normal-mode analysis for nickel porphine and nickel tetraphenylporphine from resonance Raman and infrared spectra and isotope shifts

Journal Article · Thu Jan 11 00:00:00 EST 1990 · Journal of Physical Chemistry; (USA)

DOI:https://doi.org/10.1021/j100364a007· OSTI ID:6711700

Li, Xiaoyuan; Czernuszewicz, R S; Su, Y O; Spiro, T G ^[1]; Kincaid, J R ^[2]

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1. Princeton Univ., NJ (USA)
2. Marquette Univ., Milwaukee, WI (USA)

Resonance Raman spectra with variable-wavelength excitation are reported for Ni{sup II} porphine (NiP) and for the pyrrole-d{sub 8}, meso-d{sub 4}, and (pyrrole + meso)-d{sub 12} isotopomers, as well as for Ni{sup II} meso-tetraphenylporphine (NiTPP) and its pyrrole-{sup 15}N{sub 4}, pyrrole-d{sub 8}, {sup 13}C{sub 4}-meso, and phenyl-d{sub 20} isotopomers. All the Raman-active in-plane modes have been identified and are assigned to local coordinates which take into account the phasing of adjacent bond stretches within the pyrrole rings and at the methine bridges. The IR spectra of NiP and its isotopomers are also assigned. For most of the local coordinates good frequency agreement is seen for the different symmetry blocks, showing that longer range phasings have minor effects. These in-plane mode assignments are supported by normal-coordinate calculations with a physically reasonable valence force field, which is nearly the same for NiP and NiTPP. The principal force constants are in good accord with bond length relationships selected on the basis of scaled ab initio calculations. The phenyl substituents of NiTPP lower the frequencies of the asymmetric methine bridge stretching modes {nu}{sub 10}(B{sub 1g}) and {nu}{sub 19}(A{sub 2g}) by {approximately}60 cm{sup {minus}1}; this shift is attributable partly to the loss of coupling with the C{sub m}H bending modes in NiP and partly to an electronic effect of the phenyl group. There are also near-resonant interactions in NiTPP between porphyrin and phenyl modes near 740 and 200 cm{sup {minus}1} resulting in strongly displaced modes. Otherwise the phenyl groups have little influence on the porphyrin skeletal mode frequencies. Several phenyl modes are subject to moderate RR enhancement, probably via intensity borrowing from nearby porphyrin modes.

• OSTI ID: 6711700
• Journal Information: Journal of Physical Chemistry; (USA), Vol. 94:1; ISSN 0022-3654
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
59 BASIC BIOLOGICAL SCIENCES
PORPHYRINS
INFRARED SPECTRA
RAMAN SPECTRA
DATA ANALYSIS
ENERGY LEVELS
EXPERIMENTAL DATA
ISOTOPE EFFECTS
MEASURING INSTRUMENTS
MEASURING METHODS
NICKEL
VALENCE
CARBOXYLIC ACIDS
DATA
ELEMENTS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
METALS
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
SPECTRA
TRANSITION ELEMENTS
400202* - Isotope Effects
Isotope Exchange
& Isotope Separation
550200 - Biochemistry