A copper–copper bond by intent

The ESR spectra for a series of binuclear trigonal bipyramidal copper complexes show that the SOMO is largely composed of the two equivalent dz2 orbitals on copper; the temperature independence of the ESR parameters shows that this is a relatively strong bond, and since the unpaired electron is antibonding, the σ-bond must be even stronger; these results are contrasted with the more common situation that arises when the electron is shared between two dx2–y2 type orbitals.