Comparative stability constants for metal ions with tetraazamacrocycles of various ring sizes carrying a single amine or carboxylate pendant group

Abstract

Acid dissociation constants for a series of tetraazamonocycloalkanes of {13}-{15} membered ring sizes, as well as for a related 'reinforced' {15R} tetraazabicycloalkane, each with one primary amine or carboxylate C-pendant, are reported. Further, formation constants with the metal ions Zn^II, Cd^II, Pb^II, Hg^II, Mn^II and Co^II have been determined. The ligands differ in their selection of metal ions, reflected in the formation constants for 1:1 complexation (KML). Differences arise in part from the increasing ring size or rigidity and also from the availability of potential pendant O-donors versus N-donors in stepping from amine to carboxylate pendant lignads, implying a role for the bendants in binding the metal ions.