Creation of controlled Bronsted acidity on a zeotypic mesoporous chromium(III) carboxylate by grafting water and alcohol molecules

This paper reports a new way of modulating the strength of the Bronsted acid sites of a porous solid. Our approach consists of the grafting of various polar molecules (H2O, CD3OH, CF3CH2OH, and (CF3)(2) CHOH) on MIL-100(Cr), a mesoporous crystallized chromium carboxylate with accessible unsaturated metal sites. We demonstrate, using infrared spectroscopy, that all these compounds do coordinate on the coordinatively unsaturated Cr3+ sites. This generates controlled Bronsted acid sites whose strength, measured by CO adsorption at 100 K, depends on the nature of the adsorbate. It can vary from H-0 = -3 (CD3OH) to -8 ((CF3)(2)CHOH).