Transmetallation of the dilead(II) complex [Pb2(L1′)](ClO4)4 [L1′ is the (4+4) Schiff-base macrocycle derived from 3,6-diformylpyridazine and 1,3-diaminopropane] with copper(II) perchlorate results in the formation of a dicopper(II) complex of the (2+2) Schiff-base macrocycle L1, CuII2(L1)(ClO4)4 (1). Copper(II) is unable to template the formation of 1 from the organic precursors. A series of six dicopper(II) complexes of L1 has been prepared from 1, including: [CuII2(L1)X2](ClO4)2 (where X=Cl−2, Br−3, I−4, NCS−5), CuII2(L1)(H2O)2(NO3)2(ClO4)2 (6) and CuII2(L1)(H2O)2(ClO4)4 (7). Three of these dicopper(II) complexes, 12MeCN, 2H2O and 7, have been characterised by X-ray crystallography. In all three cases the (2+2) macrocycle provides a double pyridazine bridge between the two copper(II) ions. Magnetic studies show that the double pyridazine bridge mediates strong antiferromagnetic exchange between the copper(II) ions in all of these complexes (−2J=412 to 532 cm−1). Electrochemical and spectroelectrochemical studies reveal that reduction of the dicopper(II) complexes occurs in two one electron steps, via stable mixed valent intermediates (Kc=3.8×105 to 8.6×106 in acetonitrile, MeCN), in marked contrast to all previously studied pyridazine-bridged dicopper complexes. The thiocyanate salt of the mixed valent complex, [CuIICuI(L1)(NCS)4CuI]MeCN (9), has been isolated, by transmetallation of [Pb2(L1′)](ClO4)4 with copper(I) followed by the addition of NaNCS, and structurally characterised. Finally, the previously reported grid complex, [CuI4(L1)2](PF6)4 (10) [formed by templating L1 formation on copper(I) ions], is shown by NMR spectroscopy to exist in equilibrium with another species, presumed to be a dicopper(I) complex, [CuI2(L1)(MeCN)2](PF6)2 (11), in acetonitrile solution. In support of this assignment, the structure of the dicopper(I) complex, [CuI2(L1)(PPh3)2](PF6)2 (12), isolated from reaction of 10 with two equivalents of PPh3, is reported.