Thioether S-ligation in a side-on mu-eta(2):eta(2)-peroxodicopper(II) complex

[(ANS)Cu-I(CH3CN)](+) reacts with O-2 giving [{(ANS)Cu-II}(2)(mu-eta(2):eta(2)-O-2(2-))](2+), nu(O-O) = 731 cm(-1), shown to possess S-thioether ligation, based on comparisons with analogues having all N-ligands or a -S(Ph) group. The finding is a rare occurrence and new for side-on O-2(2-) binding.