Title
Metal ion complexation studies in an aqueous solution of 1-thia-4,7-diazacyclononane, 1-thia-4,8-diazacyclodecane and 5-thia-2,8-diazanonane
Author
Faculty/Department
Faculty of Applied Engineering Sciences
Publication type
article
Publication
Oxford ,
Subject
Chemistry
Engineering sciences. Technology
Source (journal)
Polyhedron. - Oxford
Volume/pages
11(1992) :23 , p. 2989-2995
ISSN
0277-5387
ISI
A1992KC46700003
Carrier
E
Target language
English (eng)
Full text (Publishers DOI)
Abstract
The stability constants of the macrocyclic 1-thia-4,7- diazacyclononane ([9]aneN2S) and 1-thia-4,8-diazacyclodecane ([10]aneN2S) and of the open-chain 5-thia-2,8-diazanonane (atan) with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II) and lead(II) have been determined in aqueous solution (25°C, 0.1 mol dm−3 KNO3) by pH potentiometry. The complexation enthalpies with copper(II) have been determined by adiabatic calorimetry. The electronic spectra of the copper(II) and nickel(II) complexes were recorded. The magnitude of the macrocyclic effect for the copper(II) complexes is dependent upon the choice of the open-chain reference ligand and is analysed for its enthalpic and entropic contributions: a positive entropy contribution is found irrespective of the reference ligand, while the enthalpy contribution may be exothermic or endothermic. The metal ion size-based selectivity upon increase in the chelate ring size from five-membered in [9]aneN2S to six-membered in [10]aneN2S is controlled by the macrocyclic ring size: the largest drop in stability is observed for the smaller metal ions [copper(II) and nickel(II)] when [9]aneN2S is replaced by [10]aneN2S in the 1: 1 complexes. This drop in stability in the case of the 1: 1 complex with copper(II) is entirely due to an unfavourable entropy change, the complexation heat and the LF strength being higher for [10]aneN2S than for [9]aneN2S.
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