Two-dimensional Cd3-based metal–organic frameworks with halogen bonding sites for the uptake of I2

Abstract

Developing porous materials for the efficient capture of I₂ 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) [Cd₃(BTB)₂(Pz)₄]·xSol. (2), [Cd₃(BTB)₂(3-PyCN)₂(H₂O)₂]·xSol. (3), and [Cd₃(BTB)₂(4-PyCN)₄]·xSol. (4) have been prepared by ligand exchange with [Cd₃(BTB)₂(DEF)₄]·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 Cd₃ cluster secondary building units (SBUs) interconnected by BTB ligands, with each Cd₃ unit also associated with four terminally bonded ligands bearing halogen bonding sites, viz. N(DEF) for 1, N(Pz) for 2, –CN(3-PyCN) for 3, and –CN(4-PyCN) for 4. MOFs 1–4 adsorbed I₂ in the sequence 2 > 3 > 4 > 1 with a maximum uptake of 54.1 mg g⁻¹ for 2.