Model complexes of the active site of galactose oxidase (GAO) have been developed using a new ligand carrying two different phenol groups, N-[(2-hydroxy-3-methylthio-5-tert-butylphenyl)methyl]-N-[(2-hydroxy-3,5-di-tert-butylphenyl)methyl]-2-(2-pyridyl)ethylamine (L1H 2 ). Deprotonated ligand L1 2− forms a dimeric Cu(II) complex, [Cu(II) 2 (L1 2− ) 2 ], in the solid state, the structure of which has been determined by X-ray crystallographic analysis. The dimeric Cu(II)–diphenolate complex can be converted into the monomeric complex, [Cu(II)(L1 2− )(X)] (X=py, AcO, and PhCH 2 OH), in solution by adding exogenous ligands such as pyridine (py), acetate (AcO − ), or benzyl alcohol (PhCH 2 OH). The structure and physicochemical properties (UV–Vis, ESR, redox potential) of [Cu(II)(L1 2− )(X)] have been explored as a model for the resting state of the enzyme. One-electron oxidation of [Cu(II)(L1 2− )(py)] and [Zn(II)(L1 2− )(py)] by (NH 4 ) 2 [Ce IV (NO 3 ) 6 ] (CAN) yielded the corresponding phenoxyl radical/phenolate complexes, Cu(II)(L1 − ) and Zn(II)(L1 − ), respectively, which have also been characterized by UV–Vis, resonance Raman, and ESR. The structure, physicochemical properties and reactivities of the diphenolate and phenoxyl radical/phenolate complexes of L1H 2 are compared to those of the corresponding monophenolate and monophenoxyl radical complexes in order to obtain further insight into the role of Tyr 495 in the native enzyme.