SYNTHESIS OF LAYERED PEROVSKITE OXIDES, ACA2-XLAXNB3-XTIXO10 (A = K, RB, CS), AND CHARACTERIZATION OF NEW SOLID ACIDS, HCA2-XLAXNB3-XTIXO10 (0 LESS-THAN X LESS-THAN-OR-EQUAL-TO 2), EXHIBITING VARIABLE BRONSTED ACIDITY

Layered perovskite oxides of the formula ACa2-xLaxNb3-xTixO10 (A = K, Rb, Cs and 0 < x less-than-or-equal-to 2) have been prepared. The members adopt the structures of the parent ACa2Nb3O10. Interlayer alkali cations in the niobium-titanium oxide series can be ion-exchanged with Li+, Na+, NH4+, or H+ to give new derivatives. Intercalation of the protonated derivatives with organic bases reveals that the Bronsted acidity of the solid solution series, HCa2-xLaxNb3-xTixO10, depends on the titanium content. While the x = 1 member (HCaLaNb2TiO10) is nearly as acidic as the parent HCa2Nb3O10, the x = 2 member (HLa2NbTi2O10) is a weak acid hardly intercalating organic bases with pK(a) is similar to 11.3. The variation of acidity is probably due to an ordering of Nb/Ti atoms in the triple octahedral perovskite slabs, [Ca2-xLaxNb3-xTixO10], such that protons are attached to NbO6 octahedra in the x = 1 member and to TiO6 octahedra in the x = 2 member.