Enhancement of the Pfeiffer Effect Arising from the Cation-Cation Interaction

• Published in: Bulletin of the Chemical Society of Japan Vol. 50; no. 6; pp. 1476 - 1481
• Main Authors: Miyoshi, Katsuhiko, Kuroda, Yasushige, Okazaki, Hiroshi, Yoneda, Hayami
• Format: Journal Article
• Language: English
• Published: Tokyo The Chemical Society of Japan 01.06.1977; Chemical Society of Japan
• ISSN: 0009-2673; 1348-0634
• DOI: 10.1246/bcsj.50.1476

The influence of added sodium and potassium chloride, bromide, and sulfate was examined on the Pfeiffer effect of the [Co(phen)3]2+- and [Ni(phen)3]2+-d-cinchoH+ systems in water (phen=1,10-phenanthroline, and d-cinchoH+=dextro-cinchoninium ion). It was found that the added anions enhance the circular dichroism (CD) induced in the d-d transition region of [Co(phen)3]2+ and [Ni(phen)3]2+ ions, and that the CD-enhancing order is Br−>Cl−>SO42−/2. These findings were well interpreted in terms of reduced electrostatic repulsion between [Co(phen)3]2+ or [Ni(phen)3]2+ and d-cinchoH+ by the added anions, and of the resulting enhanced enantiomerization of these cationic complexes in favor of Δ-isomers in the presence of d-cinchoH+. Logarithm of the magnitude of the induced CD was found to be a linear function of logarithm of the total anion concentration in all the systems examined. This fact gives a strong support to the above interpretation, and suggests a close resemblance of these Pfeiffer-active systems to aqueous cationic surfactant solutions.