Structural and spectroscopic studies of a metacyclophane and its binuclear Cu2+ complex

In a new chelating metacyclophane, 2,9,18,25-tetraoxo-4,7,20,23-tetrakis(carboxymethyl)-1,4,7,10,17,20,23,26-octaaza[10.10]metacyclophane, the amino nitrogen atoms have a higher basicity than that of the corresponding paracyclophane, although the local electron densities on the donor atoms are identical in the two isomers. The molecular structure of a binuclear Cu2+ complex with the metacyclophane has been studied by X-ray crystal analysis: the coordination geometry around each metal ion is described by a compressed trigonal bipyramid. The solution electronic spectra of the Cu2+ complex change with pH as a result of the conversion of the coordination sites of the amide groups.