Resonance Raman frequencies and core size for low- and high-spin nickel porphyrins

Journal Article · Wed Oct 22 00:00:00 EDT 1986 · Inorg. Chem.; (United States)

DOI:https://doi.org/10.1021/ic00242a033· OSTI ID:7129741

Kim, D; Su, Y O; Spiro, T G

Resonance Raman (RR) spectra are reported with B- and Q-band excitation for nickel(II) complexes of octaethylporphyrin (OEP), protoporphyrin IX dimethyl ester (PP), and meso-tetraphenylporphine (TPP) in methylene chloride (4-coordinate, low spin) and piperidine (pip) (6-coordinate, high spin). The large core size expansion accompanying the formation of the 6-coordinate species (1.96-2.04 A) is reflected in large decreases, up to 40 cm/sup -1/ in the positions of high-frequency porphyrin skeletal modes. For NiOEP and NiPP, these are in near-quantitative accord with the core size correlations obtained previously for iron porphyrin complexes, although certain deviations due to differential coupling with the vinyl modes of protoporphyrin are noted. Contributions of a minority 5-coordinate complex to the RR spectrum of NiTPP in piperidine, previously noted on the basis of photolysis effects, are evaluated quantitatively from titration data. Formation of a monopiperidine adduct, detected previously via a RR study of NiTPP(pip)/sub 2/ photolysis, is examined for nickel meso-tetrakis(p-cyanophenyl)porphine. Equilibrium constants for successive addition of piperidine ligands, K/sub 1/ = 0.4 and K/sub 2/ = 2.5 M/sup -1/, are evaluated from optical titration data, and the absorptivities of the 5- and 6-coordinate species are found to be nearly the same, consistent with both having a high-spin configuration. The frequency of the 5-coordinate nu/sub 4/ RR band is likewise found to be much closer to the 6-coordinate than to the 4-coordinate frequency.

• Research Organization: Princeton Univ., NJ
• DOE Contract Number: AC02-81ER10861
• OSTI ID: 7129741
• Journal Information: Inorg. Chem.; (United States), Vol. 25:22
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
NICKEL COMPLEXES
SPIN-SPIN RELAXATION
PORPHYRINS
ABSORPTION SPECTROSCOPY
ADDUCTS
EQUILIBRIUM
EXPERIMENTAL DATA
LIGANDS
RAMAN SPECTROSCOPY
CARBOXYLIC ACIDS
COMPLEXES
DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INFORMATION
LASER SPECTROSCOPY
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
RELAXATION
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
400201* - Chemical & Physicochemical Properties