Equilibrium constants for pyridinium iodide charge-transfer complex formation

Edward M. Kosower, John C. Burbach

Research output: Contribution to journalArticlepeer-review


The previous formulation of the “new species” found in aqueous solutions of 1-methylpyridinium iodides as charge-transfer complexes is further confirmed by a study of the equilibrium constants for complex formation. While the K for association of 1-methylpyridinium and iodide ions is 2.3 ± 0.3 1. mole-1, the three additional methyl groups present in 1,2,4,6-tetramethylpyridinium ion only reduce the K for complexing with iodide ion to 1.83 ± 0.31. mole-1. From comparison with the data for complexing and addition to benzene derivatives (π- and σ-complexes), it is clear that the present case fits the pattern expected for “loose” bonding, or charge-transfer complex formation. In ethanol, there is considerable association to ion-pairs and 1,2,4,6-tetramethylpyridinium iodide forms complex in accordance with Beer's law over certain concentration ranges. comparison of “absorption” curves for the complex in ethanol and water indicates that the absorption band is shifted to longer wave lengths in solvents of lower solvating ability, as had been suggested previously.

Original languageEnglish
Pages (from-to)5838-5842
Number of pages5
JournalJournal of the American Chemical Society
Issue number22
StatePublished - 1 Nov 1956
Externally publishedYes


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