The two ligands L1 and L2, consisting of two 1, 4, 7-triazacyclononane rings bridged by a pyrazole or a triazole group, form with Cu2+, Ni2+ and Zn2+ a series of mononuclear [MLHn](n+ 2)+(n=− 3,− 2,− 1, 0, 1, 2) and dinuclear species [M2LHm](m+ 4)+(m= 0,− 1,− 2,− 3), the stabilities of which have been determined by potentiometric titrations. The triazole bridged ligand L1 forms complexes which are more stable than those of the pyrazole ...