In:
European Journal of Inorganic Chemistry, Wiley, Vol. 2005, No. 13 ( 2005-07), p. 2714-2726
Abstract:
X‐ray absorption spectroscopy was used to elucidate how hybrid xerogels complexed with CuCl 2 could reversibly bind molecular dioxygen. Difference EXAFS analyses at the Cu K‐edge suggest that dioxygen could bridge two Cu atoms in a μ‐η 1 :η 1 peroxo‐like conformation with unequal Cu ··· O distances. Only the short distance ( R Cu–O1 = 1.86 ± 0.01 Å) was unambiguously determined and looks typical of a Cu II site. The Cu ··· Cu internuclear distances would be rather long: R Cu–Cu ≈ 4.0 Å (3.9 Å) for the oxygenated (oxygen‐free) xerogels. Cl K‐edge EXAFS spectra revealed the pre‐existence in the oxygen‐free xerogels of Cu I sites with short Cl–Cu bonds (2.11 ± 0.03 Å). Pentacoordinate Cu II sites with a longer Cl–Cu bond (2.45 ± 0.03 Å) were also identified. Another signal at a further distance (2.73 ± 0.03 Å) suggests that the Cl ions could bridge mixed‐valence {Cu I ,Cu II } sites. In oxygenated xerogels complexed with CuCl 2 , ca. 75 % of the Cu atoms would be singly bound to dioxygen while the signature of the pentacoordinate Cu II sites would totally vanish. Substituting CuBr 2 for CuCl 2 yields xerogels with a poor capability to bind dioxygen. This is remarkably correlatedwith a decrease of the signatures at R Cu–O1 = 1.86 Å and R Cu–Cu 4.0 Å. EXAFS spectra of the oxygen‐free xerogel complexed with CuBr 2 again exhibit signatures assigned to short (2.30 Å)/long (2.49 Å) Cu–Br bonds as expected for mixed‐valence {Cu I ,Cu II } systems. Inactive xerogels prepared with metallated cyclams seem to undergo a structural change during hydrolysis and polycondensation. Deconvoluted XANES spectra of the active xerogels exhibit a strong pre‐edge resonance which is characteristic of mixed‐valence Cu I sites. This interpretation was supported by ab initio XANES simulations carried out beyond the muffin‐tin approximation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Type of Medium:
Online Resource
ISSN:
1434-1948
,
1099-0682
DOI:
10.1002/ejic.v2005:13
DOI:
10.1002/ejic.200401027
Language:
English
Publisher:
Wiley
Publication Date:
2005
detail.hit.zdb_id:
1475009-0
