X‐Ray Structures of Copper(II) and Nickel(II) Radical Salen Complexes: The Preference of Galactose Oxidase for Copper(II)

Copper or nickel? The depicted CuII salen complex, an active-site model of galactose oxidase (GO), is a localized radical in the solid state with a quinoid distribution of bond lengths in one ring. While the ligand-radical structure is not metal-dependent, the composition of the radical SOMO is. This feature may explain the much lower reactivity of the Ni complex and nature's preference for a CuII center in GO.