How Interpenetration Ensures Rigidity and Permanent Porosity in a Highly Flexible Hybrid Solid

The synthesis and the crystal structure determination, using a synchrotron microdiffraction setup, of the interwoven analogue of the highly flexible iron­(III) dicarboxylate MIL-88D structure are reported. Unlike its flexible counterpart, MIL-126, or FeIII3O­(H2O)2(OH)­[(O2C)-C12H8-(CO2)]3·n(solv), exhibits a rigid structure with an accessible three dimensional (3D) pore system resulting in a Brunauer–Emmett–Teller (BET) surface area over 1700 m2·g–1. Moreover, a large amount of coordinatively unsaturated Fe sites of +2 and +3 oxidation states are accessible to NO and acetonitrile molecules as shown by infrared spectroscopy. MIL-126 might be thus used for the removal of aromatic N-heterocyclic compounds from fossil fuel streams, as shown here in the efficient capture of indole from model benzothiophene/indole mixtures in heptane/toluene.