X-ray Absorption Studies of Three-Coordinate Dicopper(I) Complexes and Their Dioxygen Adducts

Recently, the preparation and preliminary characterization of a new series of dioxygen complexes derived from the ligand systems N4PY2, N3PY2, and N3ORPY2 have been reported. These compounds, [Cu₂L(O₂)]²⁺(4–6), are derived from well-characterized dicopper(I) complexes, [Cu₂L]²⁺(1–3), by the reversible reaction with dioxygen in dichloromethane at -80 °C (Cu:O₂= 2:1). X-ray absorption spectra of the dioxygen adducts (4–6), their dicopper(I) precursors (1–3), and other related pyridyl ligand containing Cu(I) and Cu(II) complexes are reported. The results of edge and EXAFS analysis support a description of the oxygen adducts as four- or five-coordinated peroxo-bridged dicopper(II) complexes, with Cu-Cu distances in the range 3.2-3.4 Å. Possible structures for [Cu₂(L)(O₂)]²⁺ are proposed including a novel η²:η² peroxo coordination mode. In addition, the detailed analyses of the crystallographically characterized Cu(I) precursor complexes and related Cu(II) complexes of known structure have extended to pyridyl-containing systems the validity of the multiple scattering method of EXAFS analysis (the success of which has been demonstrated recently for imidazole-containing complexes and protein derivatives).