Crystallographic Visualization of Distinct Iodic Aggregations in Isostructural Metal–Organic Frameworks

Precisely determining the location of adsorbed molecules is essential for illuminating the mechanisms underlying molecular confinement within porous metal–organic frameworks (MOFs). Here, we present the pore-filling and reactive adsorption of iodine in ALP-MOF-1 and its isostructural redox-active ALP-MOF-2. The adsorbed iodine molecules (I₂) are unaffected by Zn(II) in ALP-MOF-1 and are exclusively confined into an unusual three-dimensional (3D) iodine aggregation due to the 3D cross-linked pore topology and multiple I₂-framework interactions. Conversely, in ALP-MOF-2, the adsorbed I₂ enables the oxidation of Co(II) to Co(III), which is accompanied by the reduction of I₂ to I₃^– and the formation of I₅^– and I₂ during continuous I₂ loading. Identification of distinct iodine adsorption processes in ALP-MOF-1 and −2 motivated tuning of the metal ion composition to adjust the adsorption mechanism. The iodic aggregations in both MOFs are unambiguously confirmed by the combination of single crystal X-ray diffraction and spectroscopic characterization. The presence of multiple adsorption sites facilitate rapid iodine uptake of ∼179 wt % in ALP-MOF-1 and ∼150 wt % in ALP-MOF-2 within ∼5 h, which could be advantageous for applications requiring rapid and energy-efficient iodine capture.