Figure 2.

(a) Depiction of the HKUST-1 surface copper sites formed upon treatment of the MOF powder at 160 °C in the He flux. The resulting Cu²⁺/Cu²⁺ and Cu⁺/Cu²⁺ dimeric sites are evidenced by yellow and blue arrows, respectively. (b) Theoretical Cu L₃-edge spectra simulated for the Cu²⁺ (yellow) and Cu⁺ (blue) cations present in the Cu²⁺/Cu²⁺ and Cu⁺/Cu²⁺ dimers, respectively, and weighted by the estimated relative surface abundance. (c) Comparison between the experimental Cu L₃-edge spectrum of HKUST-1 collected at 160 °C in He flux (red) and the theoretical spectrum resulting from the weighted sum of the spectra belonging to the Cu²⁺ and Cu⁺ surface species (light purple). Constant energy cuts (dotted grey lines) are drawn in proximity of the experimental maxima of peaks A, C and D.