Structural minima of neutral and negatively charged CuO6 clusters have been investigated within density functional theory and a plane-wave approach. Among the lower energy structures, three isomers made of CuO2 complexes and two isomers featuring a double ozonide Cu(O-3) unit lie within a few hundredths of eV. Isomers containing CuOOO chains are higher in energy. Formation of Cu(O-3) units is accompanied by hybridization between O-2p- and Cu-3d-like states. We highlight analogies and differences between our results and the structural identification proposed in the framework of photoelectron spectroscopy experiments. (C) 2002 Published by Elsevier Science B.V.