Evidencing a reaction intermediate in the formation of the EuIIIbimetallic complex with p-tert-butylcalix8areneDedicated to Prof. André E. Merbach EPFL, Lausanne on the occasion of his 65th birthday.Electronic supplementary information (ESI) available: Factor analysis on 44 different experiments (Fig. S1), ES-MS spectrum of the 1 : 1 complex in dmf, recorded in absence of triethylamine and in positive mode (Fig. S2), in negative mode (Fig. S3), variable-pressure investigation between 0.1 and 202.2 MPa (Fig. S4), thermodynamic parameters calculated from data between 247 and 319 K for two complex concentrations 4.97 × 10−3and 9.95 × 10−3M at P 0.1 MPa (Fig. S5), as the concentration of nitrate increases in the solution, the absorption band at 577.9 nm decreases, indicating a shift of equilibrium towards the left Fig. S6), addition of up to 5.7 equivalents of acetic acid to a solution of the monometallic complex leads to a rapid disappearance of intermediate A followed by de-complexation

Autor:	Bünzli, Jean-Claude G., Besançon, Frédéric
Zdroj:	Physical Chemistry Chemical Physics (PCCP); 2005, Vol. 7 Issue: 10 p2191-2198, 8p
Abstrakt:	In view of the very few mechanistic information available on the complex formation between lanthanide ions and calixarenes, we study here the reaction mechanism leading to the formation of the bimetallic complex between EuIIIand p-tert-butylcalix8arene b-LH8. We show that in dmf, the 1 : 1 complex Eub-LH6NO3dmf4 partially dissociates into a compound A which is an important intermediate in the formation of bimetallic Eu2b-LH2dmf5. Several spectroscopic ES-MS, visible, luminescence, FT-IR and conductometric techniques are combined with variable-temperature and variable-pressure experiments to demonstrate that in absence of base, intermediate A is the cationic species Eub-LH6dmf4. The thermodynamic parameters of the dissociation reaction, K5298 4 ± 1 × 10−5M, ΔH0 16 ± 3 kJ mol−1, ΔS0 −30 ± 11 J mol−1K−1, as well as the reaction volume ΔV0 9.4 ± 0.9 cm3mol−1are evaluated and rationalized. In presence of triethylamine, intermediate A deprotonates to generate the neutral species A′ Eub-LH5dmf4, which, in turn, further reacts with europium nitrate to yield the bimetallic complex. In addition, the pKas of the parent calixarene LH8, of b-LH8and of p-iso-propylcalix8arene are determined in dmf, as well as the association constant between b-LH8and triethylamine, Kassoc 9 ± 1 × 103M−1.
Databáze:	Supplemental Index
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