NEW POLYOL ROUTE TO KEGGIN ION-PILLARED LAYERED DOUBLE HYDROXIDES

A new route to polyoxometalate pillared layered double hydroxides (LDHs) of the type [Mg1-x2+Alx3+-(OH)(2)][POM(n-)](x/n), where POM(n-) is the Keggin ion H2W12O406-, is reported based on the atopotactic reactions of the corresponding LDH carbonate with glycerol or triethyleneglycol at 120-130 degrees C and subsequent ion-exchange reaction of the polyol-solvated LDH intermediates with the pillaring Keggin anion. This new synthesis strategy offers important advantages over all previously reported synthesis methods, as it allows the direct conversion of readily obtainable LDH carbonates to POM-pillared derivatives. Equally important, the surface areas for the products obtained via the polyol route (similar to 160 m(2)/g) are appreciably larger than the value (83 m(2)/g) obtained for the same LDH intercalate prepared by ion exchange of an LDH hydroxide intermediate (i.e., synthetic meixnerite) with H2W12O406-. These differences in surface areas underscore the importance of synthetic methodology in mediating the micropore accessibility of pillared LDH derivatives. The acid-base functionality of the LDH-Keggin ion intercalates were examined using 2-methyl-3-butyn-2-ol (MBOH) as a reactive probe. The LDH-H2W12O406- intercalate obtained from the triethyleneglycolate intermediate exhibited high reactivity for the base-catalyzed disproportionation of MBOH, whereas the products derived from the LDH glycolate and hydroxide were relatively inactive. These differences in reactivity towards an organic substrate also emphasize the importance of synthesis methodology in regulating access in pillared LDH intercalates.