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

Abstract

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 (metal∶ligand) complexes in 95% methanol (I = 0.1 mol dm⁻³, NEt₄ClO₄; 25 °C) and crystal structures of the 1∶1 complexes of copper(II), silver(I) and lead(II) with L were determined. The structure of the copper complex shows the presence of a cation of type [CuL(NO₃)]⁺; it has a distorted octahedral geometry in which one co-ordination site is occupied by a unidentate 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-ordinate. On the other hand, the lead complex, [PbL(NO₃)(ClO₄)], is eight-co-ordinate and incorporates bidentate nitrate and unidentate perchlorate ligands. A competitive mixed-metal transport experiment across a bulk chloroform membrane incorporating L as ionophore was performed. The aqueous source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I), and lead(II) as their nitrate salts. Under the influence of a back proton gradient, silver and copper were preferentially transported to the aqueous receiving phase.