Cage-Based\nMetal–Organic Framework Featuring\na Double-Yolk Core–Shell U<sub>6</sub>L<sub>3</sub>@U<sub>18</sub>L<sub>14</sub> Structure for Iodine Capture

Cage-based MOFs, with their customizable chemical environments\nand precisely controllable nanospaces, show great potential for the\nselective adsorption of guest molecules with specific structures.\nIn this work, we have constructed a novel cage-based MOF [(CH<sub>3</sub>)<sub>2</sub>NH<sub>2</sub>]<sub>2</sub>[(UO<sub>2</sub>)<sub>2</sub>(TMTTA)]·11.5DMF·2H<sub>2</sub>O (IHEP-51), utilizing\na triazine derivative poly(carboxylic acid), 4,4′,4″-(((1,3,5-triazine-2,4,6-triyl)tris(((4-carboxycyclohexyl)methyl)azanediyl))tris(methylene))tribenzoic\nacid (H<sub>6</sub>TMTTA), as an organic ligand and uranyl as a metal\nnode. The 2-fold interpenetrated (3,6,6)-connected framework of IHEP-51\nfeatures two types of supramolecular cage structures: the Pyrgos[2]cage\nU<sub>6</sub>L<sub>3</sub> and the huge cage U<sub>18</sub>L<sub>14</sub>. They are further assembled into a double-yolk core–shell\nU<sub>6</sub>L<sub>3</sub>@U<sub>18</sub>L<sub>14</sub> structure,\nmaking it suitable for I<sub>2</sub> capture. The maximum adsorption\ncapacities of IHEP-51 for iodine in solution and gaseous iodine are\n420.4 and 1561.2 mg·g<sup>–1</sup>, respectively. XPS,\nRaman spectra, single-crystal X-ray diffraction, and DFT calculations\nreveal that the adsorbed iodine is located inside the U<sub>6</sub>L<sub>3</sub> Pyrgos[2]cage in the form of I<sub>3</sub><sup>–</sup>, thus resulting in the formation of a (I<sub>3</sub>)<sub>2</sub>@U<sub>6</sub>L<sub>3</sub>@U<sub>18</sub>L<sub>14</sub> ternary\ncore–shell structure.