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

Abstract

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).