Ligand Exchange Processes on Solvated Lithium Cations: Complexation by Cryptands in Acetone as Solvent
✍ Scribed by Ewa Pasgreta; Ralph Puchta; Achim Zahl; Rudi van Eldik
- Publisher
- John Wiley and Sons
- Year
- 2007
- Tongue
- English
- Weight
- 248 KB
- Volume
- 2007
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Kinetic studies on Li^+^ exchange between the cryptands C222 and C221 and acetone as solvent were performed as a function of ligand‐to‐metal ratio, temperature and pressure using ^7^Li NMR spectroscopy. Temperature and pressure dependence measurements were performed in the presence of an excess of Li^+^. The rate and activation parameters for the exchange process are: C222: k~298~ = (1.7 ± 0.5) × 10^3^ s^–1^, Δ__H__^#^ = 24 ± 1 kJ mol^–1^ and Δ__S__^#^ = –105 ± 4 J K^–1^ mol^–1^; C221: k~298~ = 2.24 ± 0.09 s^–1^, Δ__H__^#^ = 29 ± 2 kJ mol^–1^ and Δ__S__^#^ = –141 ±5 J K^–1^ mol^–1^. The influence of pressure on the exchange rate is insignificant for both ligands, such that the activation volume is around zero within the experimental error limits. The reported activation parameters suggest that the exchange of Li^+^ between solvated and chelated ions follows an associative interchange mechanism.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)