using a series of 2-(2-pyridyl)ethylamine bidentateligands (R1)Py1(R2,R3). The bidentateligand with the methyl substituent on the pyridine nucleus (Me)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(6-methylpyridin-2-yl)ethylamine) predominantly provided a (mu-eta(2):eta(2)-peroxo)dicopper(II) complex, while the bidentateligand without the 6-methyl group (H)Py1(Et,Bz) (N-benzyl-N-ethyl-2-(2-pyridyl)ethylamine) afforded