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 (Fe3O)-O-III(H2O)(2)(OH)-[(O2C)-C12H8-(CO2)](3)center dot 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 m(2).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.