Co-ordination tendencies of two novel compartimental oxo-aza macrobicycles. Crystal structure of a Cu(II) (H2O) inclusion complex

The two novel aza-oxa cryptands 16,21-dimethyl-4.7,10-trioxa-1,13,16,21-tetraazabicyclo[11.5.5]- tricosane-(L(1)) and 19.24-dimethyl-4.7.10,13-tetraoxa-1,16,19,24-tetraazabicyclo [14.5.5]hexacosane (L(2)) bind in aqueous solution Li+ or Na+ as well as Cu2+, Zn2+ or Cd2+. The co-ordination features of the above receptors have been studied in aqueous solution by potentiometric (298.1 or 318.1 K, / = 0.15 mol dm(-3)) and spectroscopic (H-1 and C-13 NMR and UV/VIS) techniques. In the case of Cu2+, Zn2+ and Cd2+ both the thermodynamic and spectroscopic data are in accord with the metal centres co-ordinated by the tetraaza moiety of the receptor. The co-ordination sphere is completed by binding water molecules or an oxygen of the polyoxa chain. The crystal structures of [CuL(1)][ClO4](2).0.4MeOH and [CuL(2)(H2O)][ClO4](2) have been determined. In the former the metal ion is bound by the four nitrogens and by an oxygen donor of the ligand giving rise to a rather distorted square-pyramidal co-ordination geometry In the latter the four nitrogen atoms of the ligand are again involved in the co-ordination to the metal ion; the resulting geometry is fairly distorted square-pyramidal, with the fifth co-ordinative position occupied by the oxygen of a water molecule. The Cu(H2O) unit is encapsulated inside the molecular cavity, stabilized by hydrogen bonds between the water molecule and the four oxygens of the receptor. Consequently, the Cu-O distance is remarkably short (2.09 Angstrom). This complex can lose the co-ordinated water molecule both in non-aqueous solution and in the solid state. The acidic dissociation of the Cu2+ complexes has also been studied in 1 mol dm(-3) HClO4 at different temperatures and the rate constants and activation parameters determined.