Macrocyclic ligands with pendant phosphonic acid groups

Abstract

Small aza- and oxaaza-macrocycles bearing two aliphatic nitrogens have been derivatised with pendant methylenephosphonates. Multinuclear NMR studies (³¹P and ¹H) have elicited the protonation behaviour of one of these macrocycles. Improved methods of separation and purification of the ligands are discussed. The crystal structure of the parent 1,4,7-triazacyclononane-1,4,7-triyltris(methylenephosphonic acid) has been determined, indicating that two of the nitrogens are protonated under the conditions of crystallisation. Extensive hydrogen-bonding networks are evident in the structure. The Cambridge Structural Database has been used to survey structures based on 1,4,7-triazacyclononane and other amino(alkylphosphonates), amino(alkylphosphinates), and amino(alkanecarboxylates) and their metal complexes, for comparison.