6533b82dfe1ef96bd12911b4

RESEARCH PRODUCT

Structure of Dioxygen Binding Xerogels Incorporating Cyclams Complexed with CuCl2 Salts

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X-ray absorption/emission spectroscopies were combined in order to elucidate how hybrid xerogels complexed with CuCl2 could bind reversibly O2. Difference EXAFS analyses at the Cu K-edge revealed the existence of binuclear structures with long Cu...Cu distances, i.e. RCu–Cu ≈ 3.98 A and 3.87 A for the oxygenated and oxygen-free xerogels. In oxygenated xerogels, dioxygen would bridge two Cu atoms in a μ-η1 : η1 peroxo-like conformation. The Cu-O signal found at short distance (RCu−O1 = 1.85 ± 0.01 A) is fully consistent with 40% of O2 molecules being chemisorbed per Cu site. In oxygen-free xerogels, Cl K-edge EXAFS revealed the presence of CuI sites with short Cl-Cu bond lengths (RCl−Cu = 2.11 ± 0.03 A) and of pentacoordinated CuII sites with longer Cl-Cu bond lengths (RCl−Cu = 2.45 ± 0.03 A). Another signal at RCl−Cu ≈ 2.73 A may suggest that Cl could bridge [CuI, CuII] sites. Deconvoluted XANES spectra of the active xerogels exhibit a strong preedge resonance that was assigned to the CuI sites. The chemical shifts of the Cu Kβ1,3 lines also confirmed the coexistence of CuI, CuII sites.