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Nonporous Organic Solids Capable of Dynamically Resolving Mixtures of Diiodoperfluoroalkanes

Science  13 Mar 2009:
Vol. 323, Issue 5920, pp. 1461-1464
DOI: 10.1126/science.1168679

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Abstract

Halogen bonding has increasingly facilitated the assembly of diverse host-guest solids. Here, we show that a well-known class of organic salts, bis(trimethylammonium) alkane diiodides, can reversibly encapsulate α,ω-diiodoperfluoroalkanes (DIPFAs) through intermolecular interactions between the host's I anions and the guest's terminal iodine substituents. The process is highly selective for the fluorocarbon that forms an I···I(CF2)mI···I superanion that is matched in length to the chosen dication. DIPFAs that are 2 to 12 carbons in length (common industrial intermediates) can thereby be isolated from mixtures by means of crystallization from solution upon addition of the dissolved size-matched ionic salt. The solid-state salts can also selectively capture the DIPFAs from the vapor phase, yielding the same product formed from solution despite a lack of porosity of the starting lattice structure. Heating liberates the DIPFAs and regenerates the original salt lattice, highlighting the practical potential for the system in separation applications.

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