Coordination and structural studies of crowned-porphyrins.

Simple chelating agents have been synthesized using a porphyrin and a covalently linked crown-ether. Depending on the relative spatial arrangement of both motifs, the resulting ligands, either a macrotricycle or bis-macrocycles, differ one from another by their flexibility or their aptitude to chelate bivalent or trivalent cations. The coordination chemistry as well as the structural study of these ligands and complexes are reported. In the particular case of the macrotricycle, the crown-ether motif, perpendicular to the porphyrin induces a side selectivity for the coordination of lead(II) outside the cavity. Furthermore, the coordination of zinc(II) implies a change of conformation of the ligand in which the crown-ether is parallel to the porphyrin.