Fig. 2. Identifying Cl⁻ location.

a Cl⁻ (green sphere) is resolved in the CTD using Long-wavelength experiment for Cl⁻ identification. Cl⁻ coordinates four water molecules (red spheres) through ion-dipole interactions at distances of 3.0–3.2 Å (HOH16, HOH23, and HOH46) and 4.0 Å (HOH41). b Overall structure anomalous difference density Fourier maps at 2.9 keV (green) and 2.8 keV (light orange). The regions where green density is present and light orange density where it is absent indicate the presence of Cl (red dot). In the instances where the Cl atom could not be modelled due to a sigma greater than 6, dummy atoms have been placed to indicate the potential location (dots). c Close-up view of the modelled Cl⁻ site (red dot) with the 2.9 keV anomalous difference Fourier map density surrounding it (green). d The newly identified water molecules as described in Supplementary Table 2. e A total of 401 water molecules (red spheres) were resolved in the OCP structure reported herein.