Résumé
Selective separation of bromine (Br2) from iodine (I2) remains a fundamental bottleneck in industrial halogen separation and applied bromination chemistry. A safe, efficient, and selective Br2 supply is indispensable for large-scale transformations and product purity, yet separation is complicated by their comparable kinetic diameters (3.5 and 4.0 & Aring;, respectively) and strong tendency to form interhalogen species. Conventional capture technologies remain hindered by limited stability, low capacity, and poor selectivity. Here, structurally tunable squaramine-based [2+2] macrocycles with intrinsic cavity diameters (similar to 3.5 & Aring;) are introduced as efficient and selective molecular sieves. The pristine squaramine [2+2] macrocycle achieves high Br2 uptake of 4.9 g.g-1 from cyclohexane solution and 5.7 g.g-1 in the vapor phase, while its hydrochloride derivative ([2+2].HCl) displays substantial Br2 uptake (4.3 g.g-1 cyclohexane, 3.0 g.g-1 in vapor) and completely excludes I2 even under concentrated mixed-halogen conditions. Single-crystal X-ray diffraction revealed a chloride-to-bromide exchange mechanism stabilizing unique polybromide species, further supported by UV-vis, XPS, Raman spectroscopy, and metadynamics simulations. These findings establish squaramine [2+2] as the first macrocyclic molecular sieves for selective Br2 capture and total I2 rejection, offering robust and scalable platforms for halogen separation, environmental remediation, and safe, easy-to-handle Br2 reservoirs for selective catalytic and synthetic bromination processes.