COMPLEXATION OF METAL-IONS WITH AZACROWN ETHERS BEARING AN 8-HYDROXYQUINOLINE SIDE ARM

Citation
Xx. Zhang et al., COMPLEXATION OF METAL-IONS WITH AZACROWN ETHERS BEARING AN 8-HYDROXYQUINOLINE SIDE ARM, Journal of inclusion phenomena and molecular recognition in chemistry, 29(3-4), 1997, pp. 259-268
Citations number
26
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Chemistry,Crystallography
ISSN journal
0923-0750
Volume
29
Issue
3-4
Year of publication
1997
Pages
259 - 268
Database
ISI
SICI code
0923-0750(1997)29:3-4<259:COMWAE>2.0.ZU;2-I
Abstract
Thermodynamic quantities (log K, Delta H, and T Delta S) for the inter actions of six azacrown ethers each bearing an 8-hydroxyquinoline (CHQ ) side arm (1-6) with Na+, K+, Ba2+ and Cu2+ were determined by calori metric titration in methanol solution at 25 degrees C. The results ind icate that these ligands form, stable complexes with the cations studi ed. Ligands 1 and 3 that have CHQ attached through position 7 (next to the OH group) show high selectivity for Cu2+ (log K values of 8.12 an d 9.44, respectively) over Na+, K+, and Ba2+ by more than four orders of magnitude. On the other hand, ligands 2 and 4 that have CHQ attache d through position 2 (next to the quinoline nitrogen group) form more stable complexes with Na+, K+, and Ba2+, but less stable complexes wit h Cu2+, than ligands 1 and 3. All ligands interact more strongly with K+ than with Na+. The K+/Na+ selectivity for ligands 4 and 5 is about 1.5 log K units. All complexation reactions display negative enthalpy changes. In most cases the entropy changes are also negative, indicati ng that formation of the complexes is enthalpy driven. H-1 NMR spectra l experiments demonstrate coordination of the cations by all donor ato ms of the ligands including those of the CHQ arm. In all cases, the OH signal is observed in the H-1 NMR spectra, suggesting that the comple xation with the cations does not involve deprotonation of the CHQ grou ps in the ligands.