EFFECTS OF PH AND MG-GA RATIO ON THE SYNTHESIS OF GALLIUM-CONTAINING LAYERED DOUBLE HYDROXIDES AND THEIR POLYOXOMETALATE ANION EXCHANGED PRODUCTS

We have synthesized a series of [Mg-(1-x(2+))M-x(3+)(OH)(2)][TA((x/2)( 2-))]. zH(2)O (M3+ = Ga3+ or Al3+ and TA = C6H4(COO-)(2)) from mixed-m etal chloride solutions with initial M3+ mole fractions of 0.20, 0.25, and 0.33, at constant pH values of 6.8, 7.7, 8.6, and 10.0. Terephtha late-containing products were obtained only under conditions that resu lted in a Mg:M3+ ratio of 2:1 in the mixed metal hydroxide layers, ind icating that a high layer charge density is necessary to incorporate t erephthalate anions between the inorganic layers. Anion-exchange react ions were subsequently performed to produce LDHs intercalated with PW1 1O397- and H2W12O406- anions, yielding products that displayed sharp p owder diffraction patterns. In each case, the surface area of the POM- intercalated product was found to be approximately 40-45 m(2)/g, indic ating that the micropore system is totally blocked and that the materi als are virtually nonporous; this may result from the high layer charg e density of the LDH-terephthalate precursors.