Reaction of 2,6-diacetylpyridine or 2,5-diformylpyridine with a variety of diprimary amines in the presence of large alkaline earth metal ions acting as templates yields complexes of [2 + 2 ] macrocyclic Schiff bases in good yield. The single template ion may be replaced by Cu(II), and other transition metal ions, to afford binuclear complexes in most cases. The bi-Cu(II) complexes may act as receptors for one or two small bridging substrate molecules or ions including OH −, OR −, halide, N − 3, NCS −, NCSe −, pyrazolate, imidazolate, and pyrazine. Anti-ferromagnetic superexchange coupling has been recognized and measured by means of measurements of magnetic susceptibility and e.s.r. spectra. X-ray crystal structures of several of the complexes are described. The relationships between the macrocycle cavity size and the nature and mode of attachment of the bridging substrate are discussed. Some di-μ-hydroxo and alkoxo bi-Cu(II) complexes undergo ready reduction to bi-Cu(I) with accompanying oxidative coupling of available substrate molecules. The structure of a tetranuclear Cu(I) cluster containing phenylacetylide is described.