Fig. 5. (a) DFT-optimized structural models for framework-interacting Cu-species dominating Cu-speciation in He-activated Cu-CHA at 400 °C, namely 1Al Z[Cu(ii)(OH)], 1Al ZCu(i), and 2Al Z₂Cu(ii) sites. The atoms located at the first and second coordination shell of Cu are shown in ball-and-stick mode (atom colour code: Cu, green; H, white; O, red; Si, grey; Al, yellow) and highlighted with coloured circles indicating the different coordination shells included in the EXAFS fitting model (Cu–O_ef: wine; Cu–O_fw: red; Cu–O′_fw: orange; Cu–T_fw: blue). For each shell, the average bond distances from Cu refined by mono-component EXAFS fits are reported in Å, whereas the correspondent starting values from DFT are reported in parentheses. (b) Comparison between experimental (black circles) and best fit (light grey thick lines) FT-EXAFS spectra (top panels: magnitude, bottom panels: imaginary part) obtained from multi-component fits on the whole Cu-CHA sample series; for each sample, the weighted contributions from the three dehydrated Cu-species included in the fitting model are also reported as thin solid lines (1Al Z[Cu(ii)OH]: grey, 1Al ZCu(i): red; 2Al Z₂Cu(ii): orange). The correspondent experimental and best fit k ² χ(k) curves in k-space can be found in the ESI, Section 5.5.† In part (b), sample composition is indicated by (Cu/Al; Si/Al) labels.