Coordination properties of a new hexaazamacrocycle containing thiophene units as pendant arms

The synthesis of the macrocyclic ligand 1,4,7,13-tetramethyl-10,16-bis(o-th iophenylmethyl)-1,4,7,10,13,16-hexaazacyclooactade- cane (L2) is reported. This compound presents a hexaaza macrocyclic backbone bearing two thiopheny lmethyl side arms. Ligand protonation and Cu(II), Zn(II), Cd(II) and Pb(II) coordination were studied by means of potentiometric measurements. In the metal complexes all nitrogens seem to be involved in metal coordination, wh ile the sulfur atoms of the heteroaromatic subunits do not participate in m etal binding, as confirmed by the crystal structure of [PbL2Cl]. BPh4. In t he [PbL2Cl](+) cation the metal is enveloped by the macrocyclic ligand, coo rdinated by the six nitrogens and a chloride anion with a distorted monocap ped trigonal prismatic geometry. Although L2 forms complexes of lower stabi lity with respect to other N-functionalized hexaaza-macrocycles, this ligan d displays selective coordination of the larger Cd(II) and Pb(II) over Zn(I I). All the metal complexes under investigation are readily extractable fro m aqueous solutions to organic solvents. Therefore, L2 is a promising selec tive extracting agent for metal cations. (C) 2000 Elsevier Science S.A. All rights reserved.