Microporous aluminum bisphosphonates

Several bisphosphonates of trivalent elements (Al, Ga and La) have been prepared under different synthetic conditions in order to induce microporosity. Two bisphosphonic acids, 4,4′-biphenylenebis(phosphonic acid), [H2O3P–C6H4]2, and 4-(4-phosphonophenoxy)phenyl phosphonic acid, [H2O3P–C6H4]2–O, have been used as crosslinking agents. The materials have been characterized by a number of techniques including N2 adsorption–desorption isotherms and temperature-programmed desorption of ammonia to characterize the specific surface and acid properties, respectively. Crosslinked hybrid materials with surface areas ranging between 100 and 400 m2/g and textural properties varying from non-porous to mainly microporous can be isolated. The use of inexpensive phenylphosphonic acid as a spacer group has also been studied. The experimental conditions to get microporous solids with specific surface areas as high as 400 m2/g are described. Usually, the compounds contain both mesopores and micropores. The micropore size distributions are centered between 7 and 20 Å.