Titanium is a very attractive candidate for MOFs due to its low toxicity, redox activity, and photocatalytic properties. We present here MIL-125, the first example of a highly porous and crystalline titanium(IV) dicarboxylate (MIL stands for Materials of Institut Lavoisier) with a high thermal stability and photochemical properties. Its structure is built up from a pseudo cubic arrangement of octameric wheels, built up from edge- or corner-sharing titanium octahedra, and terephthalate dianions leading to a three-dimensional periodic array of two types of hybrid cages with accessible pore diameters of 6.13 and 12.55 A. X-ray thermodiffractometry and thermal analysis show that MIL-125 is stable up to 360 degrees C under air atmosphere while nitrogen sorption analysis indicates a surface area (BET) of 1550 m(2) x g(-1). Moreover, under nitrogen and alcohol adsorption, MIL-125 exhibits a photochromic behavior associated with the formation of stable mixed valence titanium-oxo compounds. The titanium oxo cluster are back oxidized in the presence of oxygen. This photochemical phenomenon is analyzed through the combined use of Electron Spin Resonance (ESR) and UV-visible absorption spectroscopies. The photogenerated electrons are trapped as Ti(III) centers, while a concomitant oxidation of the adsorbed alcohol molecules occurs. This new microporous hybrid is a very promising candidate for applications in smart photonic devices, sensors, and catalysis.

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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 FeIII 3O(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.

Waterproof MOFs … … are prepared from the reaction of ZrCl 4 with the corresponding dicarboxylic acid. In their Communication on page 9267 ff., C. Serre and co-workers show that the members of this new series of isoreticular metal-organic frameworks (MOFs) are hydrophobic, and have a one-dimensional pore system and Lewis acidity. They also have a higher hydrothermal and mechanical stability than their UiO MOF polymorph counterparts.

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