High-Performance Squaramine Macrocycles as Molecular Sieves for Selective Halogen Separation and Aromatic Bromination

Area of Science:

• Chemical Engineering
• Materials Science
• Separation Science

Background:

• Selective separation of bromine (Br2) from iodine (I2) is challenging due to similar properties.
• Existing capture technologies lack stability, capacity, and selectivity.
• A reliable bromine supply is crucial for industrial bromination chemistry.

Purpose of the Study:

• To develop efficient and selective molecular sieves for bromine capture.
• To achieve complete rejection of iodine during separation.
• To create a safe and scalable platform for bromine handling and application.

Main Methods:

• Synthesis of structurally tunable squaramine-based [2+2] macrocycles.
• Evaluation of Br2 and I2 uptake using cyclohexane solutions and vapor phases.
• Characterization using single-crystal X-ray diffraction, UV-vis, XPS, and Raman spectroscopy.
• Computational analysis via metadynamics simulations.

Main Results:

• Pristine squaramine [2+2] achieved high Br2 uptake (4.9 g/g in solution, 5.7 g/g in vapor).
• The hydrochloride derivative ([2+2].HCl) selectively captured Br2 while completely excluding I2.
• Mechanism revealed a chloride-to-bromide exchange stabilizing polybromide species.

Conclusions:

• Squaramine [2+2] macrocycles are the first to enable selective Br2 capture and total I2 rejection.
• These sieves offer robust platforms for halogen separation and environmental remediation.
• The technology provides safe, easy-to-handle bromine reservoirs for synthetic applications.