Two-dimensional Cd-3-based metal-organic frameworks with halogen bonding sites for the uptake of I-2

Developing porous materials for the efficient capture of I-2 is relevant to the sequestration and storage of radioactive iodine towards clean nuclear energy. In this work, three topologically identical two-dimensional (2D) metal-organic frameworks (MOFs) [Cd-3(BTB)(2)(Pz)(4)]center dot xSol. (2), [Cd-3(BTB)(2)(3-PyCN)(2)(H2O)(2)]center dot xSol. (3), and [Cd-3(BTB)(2)(4-PyCN)(4)]center dot xSol. (4) have been prepared by ligand exchange with [Cd-3(BTB)(2)(DEF)(4)]center dot 2(DEF)(0.5) (1) via single-crystal to single-crystal transformations (H3BTB = benzene-1,3,5-tribenzoic acid; DEF = diethylformamide; Pz = pyrazine; 3-PyCN = 3-cyanopyridine; 4-PyCN = 4-cyanopyridine; xSol. = guest solvates). MOFs 1-4 feature linear Cd-3 cluster secondary building units (SBUs) interconnected by BTB ligands, with each Cd-3 unit also associated with four terminally bonded ligands bearing halogen bonding sites, viz. N(DEF) for 1, N(Pz) for 2, -C =N(3-PyCN) for 3, and -CN(4-PyCN) for 4. MOFs 1-4 adsorbed I-2 in the sequence 2 > 3 > 4 > 1 with a maximum uptake of 54.1 mg g(-1) for 2.