Iodine adsorption studies of dipalladium-based supramolecular cages

Four water-soluble cage-like hosts (1·4NO₃^-: {[(bpy)₂Pd₂]₂L¹₂}(NO₃)₄, 2·4NO₃^-: {[(bpy)₂Pd₂]₂L²₂}(NO₃)₄, 3·6NO₃^-: {[(bpy)₂Pd₂]₃L³₂}(NO₃)₆ and 4·6NO₃^-: {[(bpy)₂Pd₂]₃L⁴₂}(NO₃)₆) have been successfully self-assembled by coordinating the flexible amide based polypyrazole ligands (H₂L¹: N¹,N⁴-di(1H-pyrazol-5-yl)terephthalamide, H₂L²: N¹,N⁴-bis(3-methyl-1H-pyrazol-5-yl)-terephthalamide, H₃L³: N¹,N³,N⁵-tri(1H-pyrazol-5-yl)benzene-1,3,5-tricarboxamide and H₃L⁴: N¹,N³,N⁵-tris(3-methyl-1H-pyrazol-5-yl)benzene-1,3,5-tricarboxamide) with dipalladium corners ([(bpy)₂Pd₂(NO₃)₂](NO₃)₂, where bpy = 2,2΄-bipyridine) in aqueous solution. Their structures were characterized by ¹H NMR, ESI-MS and single-crystal X-ray diffraction. Notably, all the four supramolecular assemblies are capable of adsorbing iodine molecules via halogen bonds and other supramolecular interactions.