Copper(I)/(II) complexes with the ligand 2-aminoethyl(2-pyridylmethyl)1,2-ethanediamine (apme, abbreviated as PDT in the literature as well) were prepared and characterized. Crystal structures of the copper(I) complexes, [Cu 2 (apme) 2 ]X 2 (1, 2; X=ClO 4 , CF 3 SO 3 ), showed that they are dinuclear, in contrast to the trigonal bipyramidal copper(II) complexes [Cu(apme)Cl]BPh 4 (3) and [Cu(apme)(DMF)](BPh 4 ) 2 (4). 1 and 2 could be investigated in solution by NMR spectroscopy and 3 and 4 by cyclovoltammetry. From the results of these studies it is clear that in solution equilibria between the dinuclear complexes 1/2 and another species exist, most likely the monomeric [Cu(apme)CH 3 CN] + . Time-resolved UV/vis spectra at low temperatures allowed the spectroscopic detection of dioxygen adduct complexes as reactive intermediates during the oxidation of 1/2 with dioxygen that seem to play an important role in copper enzymes such as peptidylglycine-α-hydroxylating monooxygenase (PHM).