Surface Acid-Base Properties of Porous Prussian Blue Analogues

Surface acid-base properties of two compositions of porous Prussian blue analogues, Co3[Co(CN)6]2 and Zn3[Co(CN)6]2, are discussed from inverse gas chromatography data recorded in the 473–513 K temperature range. These compositions are representatives of the structural features, cubic (Co) and rhombohedral (Zn) unit cell, found in that family of porous coordination polymers. Chromatographic profiles at infinite dilution were recorded for neutral, acidic and basic probe molecules. For the cubic phase, with partially naked metal centers at the cavities surface, the material has acidic character (KA = 0� 32 and KB = 0� 12) but, for the rhombohedral one, a slightly basic behavior was found (KA = 0� 25 and KB = 0� 27) related to the electron density concentration on the N atom. In this structure the surface of the cavities is formed by N atoms from ZnN4 tetrahedra. These results herein discussed contribute to understand the acid-base interactions in Prussian blue analogues, including their performance in adsorption and separation of mixtures of gases and vapors by these porous solids.