Density functional theory (DFT) calculations have been carried out for a series of Cu^I complexes bearing N-hexadentate macrocyclic dinucleating ligands and for their corresponding peroxo species (1c–8c) generated by their interaction with molecular O₂. For complexes 1c–7c, it has been found that the side-on peroxodicopper(II) is the favored structure with regard to the bis(-oxo)dicopper(III). For those complexes, the singlet state has also been shown to be more stable than the triplet state. In the case of 8c, the most favored structure is the trans-1,2-peroxodicopper(II) because of the para substitution and the steric encumbrance produced by the methylation of the N atoms. Cu^II complexes 4e, 5e, and 8e have been obtained by O₂ oxidation of their corresponding Cu^I complexes and structurally and magnetically characterized. X-ray single-crystal structures for those complexes have been solved, and they show three completely different types of Cu^II₂ structures: (a) For 4e, the Cu^II centers are bridged by a phenolate group and an external hydroxide ligand. The phenolate group is generated from the evolution of 4c via intramolecular arene hydroxylation. (b) For 5e, the two Cu^II centers are bridged by two hydroxide ligands. (c) For the 8e case, the Cu^II centers are ligated to terminally bound hydroxide ligands, rare because of its tendency to bridge. The evolution of complexes 1c–8c toward their oxidized species has also been rationalized by DFT calculations based mainly on their structure and electrophilicity. The structural diversity of the oxidized species is also responsible for a variety of magnetic behavior: (a) strong antiferromagnetic (AF) coupling with J = -482.0 cm^-1 (g = 2.30; = 0.032; R = 5.6 × 10^-3) for 4e; (b) AF coupling with J = -286.3 cm^-1 (g = 2.07; = 0.064; R = 2.6 × 10^-3) for 5e; (c) an uncoupled Cu^II₂ complex for 8e.