Interaction of transition- and post-transition-metal ions with O₂N₂-donor macrocycles incorporating pendant pyridylmethyl groups

The interaction of cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) with pyridylmethyl pendant-arm derivatives of O₂N₂-donor macrocycles incorporating from 14- to 17-membered rings has been investigated. Thermodynamic stabilities of the 1:1 (metal:ligand) complexes have been determined in 95% methanol (I = 0.1 mol dm^-3, NEt₄ClO₄; 25°C). The data indicate that the pyridyl nitrogens participate in co-ordination to the respective metals in each complex in solution. The crystal structures of the nickel(II) and copper(II) complexes of the 15-membered O₂N₂-donor macrocycle containing two pendant 2-pyridylmethyl groups have also been determined. For the nickel complex only the nitrogens of the macrocyclic ring and the pendant pyridyl nitrogens are co-ordinated; overall, the co-ordination geometry is distorted octahedral, with the fifth and sixth positions being occupied by a bidentate nitrate group. In contrast, in the copper complex the four nitrogens and at least one of the two ring ether oxygens are co-ordinated (there is a long contact with the second); these two oxygens may be considered to displace those of the nitrate chelate found in the nickel complex. In the nickel complex, Ni-N are 2.119(6), 2.113(4) (aliphatic), 2.061(4), 2.032(5) (aromatic) and Ni-O 2.1 37(5), 2.230(4) Å. In the copper complex, Cu-N are 2.06(1), 2.02(1) (aliphatic), 1.97(1), 2.04(1) (aromatic) and Cu-O 2.319(9), 2.92(1) Å. The N(aliphatic)-M-N(aromatic) angles, trans within the ligand, are 111.4(2), 177.2(2) (M = Ni) and 127.6(4), 179.1 (5)°(M = Cu).