Macrocyclic ligand design. Structure–function relationships involving the interaction of pyridinyl-containing, mixed oxygen–nitrogen donor macrocycles with cobalt(ii), nickel(ii), copper(ii), zinc(ii), cadmium(ii), silver(i) and lead(ii)

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Abstract
A comparative investigation of the interaction of three dibenzo-substituted, mixed oxygen–nitrogen donor macrocycles with cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) has been carried out. The thermodynamic stabilities of the respective complexes in 95% methanol (I = 0.1; Et4NClO4, 25 °C) have been determined. All ligands form 1 ∶ 1 (metal ∶ ligand) species with the above metal ions. The results are compared with those obtained previously for related mixed-donor (cyclic) systems. Single crystal structures of six metal complexes of these 20-membered ring ligands have been determined by X-ray diffraction. All of the macrocyclic donor sites participate in binding to the metal ion in the copper(II) and cadmium(II) complexes. The copper complex is six-coordinate, while the cadmium complex is eight-coordinate with the addition of a bidentate nitrato ion. A tri-nuclear complex is formed on complexation with silver(I) in which two silver-containing macrocycles are linked by a bridging two-coordinate silver ion. The metal atoms in each of the cobalt(II), nickel(II) and zinc(II) complexes are six-coordinate, however, they are bound to the macrocycle only at the three secondary amine nitrogen sites. The coordination sphere is completed by two nitrato counterions in the zinc(II) complex, and by a nitrato ion and a methanol molecule in each of the cobalt(II) and nickel(II) complexes.

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