Dioxygen Activation by Photoexcited Copper Atoms

Article abstract of DOI:10.1021/ja00359a006

2P<-2S photoexcited Cu atoms react with O2 in mixed rare gas/O2 matrices to form CuO2, which is found from UV-visible absorption/fluorescence, infrared, and electron spin resonance to be spectroscopically and chemically distinct from mono(dioxygen)copper, Cu(O2), the latter being the product of the reaction of ground-state 2S Cu atoms with dilute rare gas/O2 matrices.CuO2 reacts with excess oxygen under cryogenic conditions to form copper ozonide, Cu(O3), and ozone, O3, whereas Cu(O2) yields bis(dioxygen)copper, Cu(O2)2.The bonding between the copper and oxygen atoms in CuO2 can be described as the interaction between a Cu²⁺ and two equivalent O^- ions, having covalent contributions to the Cu-O bonding, in contrast to Cu(O2), which is formulated as an interaction between Cu⁺ and O2^- ions, a tight-ion pair, having nonequivalent oxygen atoms with the odd electron residing mainly on the dioxygen moiety, that is , mono-η¹-superoxocuprous(I).Attention is focused on mechanistic aspects of the copper atom-dioxygen photochemical reaction, especially the differences in the reactivity of the Cu atom in its ground 2S and excited 2P and 2D electronic states.It is proposed that the generation of CuO2 following the 2P<-2S photoexcitation of Cu atoms in the presence of nonnearest neighbor O2 molecules involves 2P->2D relaxation, diffusion of a long-lived Cu 2D atom to an O2 molecule, and insertion of a Cu 2D atom into O2 to yield CuO2.This should be contrasted with 2S Cu atoms reacting spontaneously with a neighboring O2 molecule via electron transfer to form Cu(O2).