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The complex formation of ammonium ion in water with 1,4,8,11-tetra-azacyclotetradecane (1), 1,5,9,13-tetra-azacyclohexadecane (2), 1,5,10,14-tetra-azacyclo-octadecane (3) and 1,6,11,16-tetra-azacyclo-eicosane (4) has been studied by potentiometric titration and (1)H NMR. The results indicate that only ligands 2 and 3 form complexes with NH(+)(4) in basic solutions; the stability constants of complexes (1:1, 2:1, free and protonated) are given. The relationship between the ligand ring size, basicity, and complexation or transprotonation is discussed. An improved version of the program MICMAC allowing simultaneous least-squares adjustment of pH-titration and (1)H NMR data has been created.
Suet
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Université de Bretagne Occidental, Département de Chimie, 6, Avenue V. Le Gorgeu, 29287 Brest-Cedex, France.
Laouenan
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