Synthesis and structural characterization of metal–organic frameworks with the mellitate linker M2(OH)2[C12O12H2]·2H2O (M = Al, Ga, In) MIL-116

A new series of isostructural MOF-type carboxylates called MIL-116 (M2(OH)2[C12O12H2]·2H2O), was synthesized from the combination of mellitic acid and trivalent p cations M = Al3+, Ga3+ or In3+. Their structures were analyzed either by single-crystal microdiffraction using the synchrotron radiation beamline (ID13 station at ESRF, Grenoble) or solved from powder X-ray diffraction. The 3D hybrid framework is built up from the connection of infinite straight chains of metal-centered octahedra sharing trans corners linked to each other through the mellitate ligands. Here the ligand acts as octadentate linker with four of the carboxylic groups involved in the M–O–C bondings. The two other carboxylate arms remain non-bonded under their protonated form. This represents a rare case of the occurrence of both non-bonding and bonding organic functionalities in a MOF-type solid. Within the tunnels are located water species that interact with the non-coordinated –COOH groups pointing towards the channel.

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