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Ligand Exchange Processes on Solvated Lithium Cations: Complexation by Cryptands in Acetone as Solvent
Author(s) -
Pasgreta Ewa,
Puchta Ralph,
Zahl Achim,
van Eldik Rudi
Publication year - 2007
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200601169
Subject(s) - chemistry , cryptand , solvent , ligand (biochemistry) , associative substitution , acetone , lithium (medication) , inorganic chemistry , stoichiometry , ion , organic chemistry , catalysis , medicine , biochemistry , receptor , endocrinology
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)