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Strukturen und Moleküleigenschaften ladungsgestörter Moleküle, 54. Pyridinium‐tetraphenylcyclopentadienid‐Betain und die Einelektronen‐Oxidation zu seinem Radikalkation
Author(s) -
Bock Hans,
Nick Sabine,
Näther Christian,
Göbel Ilka,
John Andreas,
Kleine Markus
Publication year - 1994
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199519950115
Subject(s) - chemistry , pyridinium , crystallography , betaine , ring (chemistry) , pyridine , radical ion , molecule , aqueous solution , bathochromic shift , photochemistry , stereochemistry , medicinal chemistry , ion , fluorescence , organic chemistry , physics , quantum mechanics
Structures and Molecular Properties of Charge‐Perturbed Molecules, 54. — Pyridinium‐Tetraphenylcyclopentadienide Betaine and the Single‐Electron Oxidation to Its Radical Cation The 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 cos 2 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 E T solvent parameters. Cyclovoltammetry in H 2 CCl 2 /0.1 M R 4 N ⊕ ClO 4 ⊖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 F 3 CCOO ⊖ 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.