Revisiting the Dependence of Cu K-Edge X-ray Absorption Spectra on Oxidation State and Coordination Environment

Abstract

X-ray absorption spectroscopy (XAS) at the Cu K-edge is an important tool for probing the properties of copper centers in transition-metal chemistry and catalysis. However, the interpretation of experimental XAS spectra requires a detailed understanding of the dependence of spectroscopic features on the local geometric and electronic structure, which can be established by theoretical X-ray spectroscopy. Here, we present a systematic computational study of the Cu K-edge XAS spectra of selected Cu complexes based on time-dependent density-functional theory in combination with a molecular orbital analysis of the relevant transitions. For a series of Cu ammine model complexes as well as a comprehensive test set of 12 Cu(I) and 5 Cu(II) complexes, we revisit the dependence of the pre-edge region in Cu K-edge XAS spectra on oxidation state and coordination geometry. While our calculations confirm earlier experimental assignments, we can also reveal additional signatures of the ligand orbitals and identify the underlying orbital interactions. The comprehensive picture revealed by this study will provide a reliable basis for the interpretation of in situ Cu K-edge XAS spectra of catalytic intermediates.

Resilience of Cuprous Oxide under Oxidizing Thermal Treatments via Magnesium Doping

“…36,37 The change in the oxidation state of the copper atom, from Cu + into Cu 2+ , leads to the observed 3.3eV shift of the edge energy position, as confirmed by experimental 38 and theoretical studies. 39 The Extended X-ray absorption Fine Structure (EXAFS) spectraextracted via the standard background removal procedure -are shown in Figure 5 b). The XANES and EXAFS spectra versus the annealing temperature are identical for both Cu2O and Cu2O:Mg thin films, except the 450 °C annealing step.…”

Increasing Magnetic Hardness of Fe3Se4 via Cu Doping

“…As mentioned in the Introduction section, one of the motivations for our work was the knowledge that the oxidation state of +1 had been typically observed for Cu in various selenides. Nevertheless, the Cu K -edge spectra of both A-samples and B-samples exhibit a weak pre-edge feature at 8979.5 eV (Figure ), which can be assigned only to the dipole-forbidden 1s → 3d transition of the Cu 2+ ion with the single hole in the 3d orbitals . This assignment is also supported by the fact that the XANES spectrum of Cu 2 Se does not show such a pre-edge feature, with the absorption edge appearing at a notably higher energy, 8982 eV .…”

Generation and Aerobic Oxidative Catalysis of a Cu(II) Superoxo Complex Supported by a Redox-Active Ligand

“…50 Similar rising edge shakedown features are observed for Cu(II) complexes which supports our assignment of a (DHP 2−• )Cu(II) electronic structure, however we note that rising edge features are also observed for Cu(I) complexes which convolutes this assignment. [52][53][54][55] The energy of the 1s → 4p transition for 1 is lower than that for square planar Cu(II) complexes, which may reflect that the open coordination site trans to the pyrrole for this T-shaped complex stabilizes the 4px orbital and shifts the transition to lower energy. [56][57][58][59][60] Related rising edge features have also been associated with some Tshaped Cu(I) complexes, where the electric dipole-allowed 1s → 4p transition corresponds to a sharp rising edge peak, although such peaks are typically of a larger normalized intensity than what is observed for 1.…”