The ground-state electronic structure and UV-visible spectra of models for oxyhemocyanin are examined using the intermediate neglect of differential overlap model and multireference configuration interaction. The experimental features are interpreted as excitations involving the d orbitals of the Cu atoms and the valence orbitals of the peroxide bridge through which they are antiferromagnetically (AF) coupled. Our model, which replaces the histidine residues with imidazoles, reproduces correctly the higher stability of the AF singlet state and the major spectroscopic features. We examine in detail the geometry of the central part of the molecule, responsible for the activity, using the experimental electronic spectrum as a guide. We further examine the effect that deprotonation of the chelating imidazoles has on the predicted spectroscopy. The central structure that we assumed to best reproduce the spectroscopy is very similar to that obtained from BLYP density functional calculations. For comparison with other results, we also examine a model compound in which NH3 replaces histidine. For both the imidazole- and the NH3-based models, the [Cu-2((mu-eta(2):eta(2)-O-2)](2+) and [Cu-2(eta-O)(2)](2+) isomers have been considered and the results compared with available data. We conclude with the observation that the electronic structure of these compounds does depend on the redox properties of the chelating nitrogen ligands.