Investigation of Acid Sites in a Zeotypic Giant Pores Chromium(III) Carboxylate

• Published in: Journal of the American Chemical Society 2006-03, Vol.128 (10), p.3218-3227
• Main Authors: Vimont, Alexandre, Goupil, Jean-Michel, Lavalley, Jean-Claude, Daturi, Marco, Surblé, Suzy, Serre, Christian, Millange, Franck, Férey, Gerard, Audebrand, Nathalie
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Porous materials
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja056906s

A study of the zeotypic giant pores chromium(III) tricarboxylate CrIII 3OF x (OH)1 - x (H2O)2·{C6H3−(CO2)3}2·nH2O (MIL-100) has been performed. First, its thermal behavior, studied by X-ray thermodiffractometry and infrared spectroscopy, indicates that the departure of water occurs without any pore contraction and no loss in crystallinity, which confirms the robustness of the framework. In a second step, IR spectroscopy has shown the presence of three distinct types of hydroxy groups depending on the outgassing conditions; first, at high temperatures (573 K), only Cr−OH groups with a medium Brønsted acidity are present; at lower temperatures, two types of Cr−H2O terminal groups are observed; and at room temperature, their relatively high Brønsted acidity allows them to combine with H-bonded water molecules. Finally, a CO sorption study has revealed that at least three Lewis acid sites are present in MIL-100 and that fluorine atoms are located on a terminal position on the trimers of octahedra. A first result of grafting of methanol molecules acting as basic organic molecules on the chromium sites has also been shown, opening the way for a postsynthesis functionalization of MIL-100.