STABILITIES OF DIVALENT AND TRIVALENT METAL-ION COMPLEXES OF MACROCYCLIC TRIAZATRIACETIC ACIDS

Potentiometric methods have been used to determine the stability constants of complexes of trivalent metal ions of Al3+, Fe3+, Ga3+, In3+, and Gd3+ with the ligands 1-oxa-4,7,10-triazacyclododecane-N,N',N''-triacetic acid, 1, 1,7-dioxa-4,10,13-triazacyclopentadecane-N,N',N''-triacetic acid, 2, and 1,7,13-trioxa-4,10,16-triazacyclooctadecane-N,N',N''-triacetic acid, 3, and of divalent metal ions of Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ with ligands 2 and 3. To these data are added the stability constants of complexes formed by divalent metal ions with 1 and of complexes of divalent and trivalent metals ions with 1,4,7-triazacyclononane-N,N',N''-triacetic acid, 4. The metal ion affinities of the series of four triazamacrocyclic ligands with three pendant acetate donor groups are compared. The effects of the metal ions on the stabilities are discussed, and the trends in the stability constants resulting from changing the macrocyclic ring size from 9 to 18 atoms and the change in the number of donor atoms of the ligand from six to nine are described.