Interaction of transition and post-transition metal ions with oxygen–nitrogen donor macrocycles incorporating pendant hydroxyethyl and carbarnoylethyl groups

Abstract

The interaction of new derivatives of O₂N₂-donor macrocycles incorporating pendant hydroxyethyl or carbamoylethyl arms with cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) has been investigated. The thermodynamic stabilities of a range of 1 : 1 (metal:ligand) complexes of these macrocycles have been determined potentiometrically in 95% methanol (I= 0.1 mol dm^–3, NEt₄ClO₄ or NMe₄Cl; at 25 °C). Comparison of selected complexes with those of the corresponding parent (non-pendant arm) macrocycles indicates that the former derivatives show more varied co-ordination behaviour than the latter. X-Ray diffraction studies of five nickel(II) complexes have been made. The complexes containing respectively 14-, 15- and 16-membered rings and two pendant alcohol arms have similar distorted-octahedral structures. In each case the nickel ion is situated outside the macrocyclic ring with only the ring nitrogen atoms and the pendant alcohol oxygen atoms co-ordinating; the remaining sites are occupied by the oxygen atoms of a bidentate nitrate ion. In contrast, the structure of the related 15-membered, mono-pendant arm (alcohol) derivative has the nickel in the macrocyclic cavity; the near-octahedral co-ordination sphere consists of two ether oxygens and two nitrogens from the macrocyclic ring in the equatorial plane together with oxygen atoms from the pendant alcohol arm and a water molecule in the axial sites. The structure of a pendant bis(amide) derivative also incorporates the nickel in the macrocyclic cavity with the pendant amide groups co-ordinated in axial sites to yield an overall distorted-octahedral geometry.