ISSN:
0947-3440
Keywords:
Pyridinium-cyclopentadienide betaine structure
;
Redox potentials
;
ESR-ENDOR spectra
;
Radical cation
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Structures and Molecular Properties of Charge-Perturbed Molecules, 54. - Pyridinium-Tetraphenylcyclopentadienide Betaine and the Single-Electron Oxidation to Its Radical CationThe single-crystal structure of the dark-blue pyridinium-tetraphenylcyclopentadienide betaine shows the pyridine ring and the phenyl substituents twisted between 37 and 55°, indicating reduced π interactions between cos2 ω = 0.6 and 0.4. According to AM1 calculations based on the structure coordinates, the total charges of the pyridinium cation acceptor and the cyclopentadienyl anion donor amount to +0.62 and -0.53. This pronounced betaine zwitterionic character causes a 0.5 eV (!) bathochromic shift from 22000 cm-1 in aqueous to 18000 cm-1 in n-heptane solution, which can be correlated with the respective ET solvent parameters. Cyclovoltammetry in H2CCl2/0.1 M R4N⊕ClO4⊖ yields an irreversible reduction potential at -1.5 V and two oxidation potentials at +0.36 and +1.28 V, of which the lower one is reversible. With F3CCOO⊖Ag⊕, therefore, a radical cation can be generated and is characterized by ESR/ENDOR spectra. The coupling constants are satisfactorily reproduced by McLachlan calculations, which also suggest that most of the spin population should be localized within the five-membered ring.
Additional Material:
5 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.199519950115
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