Reactivity of copper(I) complexes [Cu(L)]+ containing a series of tetradentate tripodal ligands, (6-methyl-2-pyridylmethyl)m(2-pyridylmethyl)(3-m)amine (m = 1, 2, or 3) with molecular oxygen was investigated in acetone at -70-degrees-C. It was found that the introduction of 6-methyl group(s) into pyridyl group(s) has significant influences on the stereochemistry and thermal stability of peroxo dicopper(II) complexes.