Dynamic NMR Study of the Kinetics of Complexation of Tl+ Ion with Calix[4]crown-6

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• 作者：Hedayat Haddadi ; Naader Alizadeh ; Mojtaba Shamsipur ; Zouhair Asfari
• 刊名：Journal of Physical Chemistry A
• 出版年：2010
• 出版时间：July 22, 2010
• 年：2010
• 卷：114
• 期：28
• 页码：7462-7469
• 全文大小：324K
• 年卷期：v.114,no.28(July 22, 2010)
• ISSN：1520-5215

文摘

The complexation and exchange kinetics and mechanism for the dissociation and conformational change of thallium ion complex of calix[4]crown-6 were studied in CD₃CN/CDCl₃ (4:1 v/v) solution by dynamic ¹H NMR. The results show the formation of a 1:1 complex with cone conformation. From variable temperature dynamic NMR analysis in the range 223−293 K, two coalescence temperatures at 228 and 243 K were ascertained. The activation parameters for the dissociation process, E_a (kJ/mol), ΔS^‡ (J/mol.K), and ΔH^‡ (kJ/mol) are 11.0, −133.2, and 10.1 for the bimolecular regime and 21.5, −112.8, and 20.6 for the unimolecular regime, respectively. In addition, the dynamic ¹H NMR spectroscopy shows that the exchange of Tl⁺ between the two crown sides of the complexed ligand proceeds through an intramolecular tunneling. An Arrhenius convex curve was observed for intramolecular exchange. This phenomenon is explained in terms of two conformer state formations differentiated by hydrogen bond association.