Mono- and bi-nuclear copper(II) complexes with polyazacyclophane receptors containing two different binding sites

The macrobicyclic compound 1,4,7,-trimethyl-19,22,28,31-tetraoxa-1,4,7,14,23-pentaaza[9.25]-p-cyclophape (L-1) has been prepared. It comprises a N-3 and a cyclic N2O4 subunit, connected by p-phenylene spacers. Protonation of L-1 (and L-2, in which the N2O4 unit is replaced by a N-5 moiety) has been studied by means of potentiometric measurements. The compounds L-1 and L-2 bind up to five and six protons in aqueous solution above pH 2, respectively. Proton and C-13 NMR spectra at different pH values allow the determination of the stepwise protonation sites. Considering the [H4L1](4+) species the acidic protons are located on the benzylic nitrogens. Copper(II) co-ordination by L-1 and L-2 has been potentiometrically studied (298.1 K, 0.1 mol dm(3) NMe4Cl aqueous solution): L-1 forms only a mononuclear complex, while L-2 gives both mono-and bi-nuclear species in aqueous solution. In the [CuL1](2+) complex the metal is co-ordinated by the three tertiary nitrogens of the N-3 unit, while the N2O4 moiety shows a high tendency to protonation. These solution data are confirmed by the crystal structure of [Cu(HL1)Cl(H2O)][ClO4](2). In the [Cu(HL1)Cl(H2O)](2+) cation the metal is co-ordinated by the three amine groups of the triaza moiety and by a chloride anion, in a rather unusual square-planar geometry. A water molecule is encapsulated by the N2O4 moiety, held by a hydrogen-bond network. In the mononuclear [CuL2](2+) complex the Cu-II is preferentially lodged inside the pentaaza moiety. Such a complex can add a further copper(II) ion, which is co-ordinated by the N-3 binding unit.