Macrocyclic ligand design. Interaction of selected transition and post-transition metal ions with a new N2O2-donor macrocycle incorporating a pyridylmethyl pendant arm

A pyridylmethyl derivative of a 14-membered, N2O2-donor macrocycle (L) and its complexes with cobalt(II), copper(II), zinc(II), silver(I), cadmium(II) and lead(II) have been prepared. Thermodynamic stabilities of the 1 : 1 (m etal : ligand) complexes in 95% methanol (I = 0.1 mol dm(-3), NEt4ClO4; 25 degrees C) and crystal structures of the 1 : 1 complexes of copper(II), sil ver(I) and lead(II) with L were determined. The structure of the copper com plex shows the presence of a cation of type [CuL(NO3)](+); it has a distort ed octahedral geometry in which one co-ordination site is occupied by a uni dentate nitrate ligand. In contrast, the cationic silver complex is of type [AgL](+) with the two pyridine ring nitrogen atoms of L dominating the co- ordination environment, which may be regarded as essentially two-co-ordinat e. On the other hand, the lead complex, [PbL(NO3)(ClO4)], is eight-co-ordin ate and incorporates bidentate nitrate and unidentate perchlorate ligands. A competitive mixed-metal transport experiment across a bulk chloroform mem brane incorporating L as ionophore was performed. The aqueous source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), z inc(II), cadmium(II), silver(I), and lead(II) as their nitrate salts. Under the influence of a back proton gradient, silver and copper were preferenti ally transported to the aqueous receiving phase.