Figure 5.

(a) Overview of the postsynthetic exchange process and exchange molecules studied, along with the three outcomes of incorporation. (b–d) Experimental energy spectra and simulation fits of 5 MeV primary He ions backscattered from UiO-66@Si subjected to exchange conditions with (b) 3-iodobenzoic acid (UiO-66-iba) with the top simulated fit assuming a uniform distribution of the incorporated iodine (and, by proxy, the linker) and the bottom simulated fit assuming a decreasing linear gradient of iodine deeper into the crystal, with the poorer fit unambiguously demonstrating the absence of strong concentration dependence on the probed depth; (c) iodoterephthalic acid (UiO-66-ita), displaying a core–shell microstructure with a high near-surface iodine concentration; and (d) 3-iodo-4-(methoxycarbonyl)benzoic acid (UiO-66-monoester) showing a low concentration of iodine near the surface.