SYNTHESIS, STRUCTURAL CHARACTERIZATIONS, AND SOME CHEMICAL-PROPERTIES OF A FIBROUS TITANATE WITH A NOVEL LAYER TUNNEL INTERGROWN STRUCTURE

A fibrous alkali titanate with a novel layer/tunnel intergrown structure, M(6+)delta Ti16O35+delta/2 (M = K, Rb; -0.7 < delta < +0.5), has been prepared from a protonic layered tetratitanate H2Ti4O9.1.2H(2)O through a soft chemical route: adjustment of the interlayer alkali/proton composition by ion-exchange and subsequent dehydration around 350 degrees C. X-ray and electron diffraction data as well as a (010) high-resolution lattice image for the typical composition of delta = O have demonstrated that the titanate crystallizes in a primitive monoclinic system with the unit cell parameters alpha similar to 17 Angstrom, b similar to 3.8 Angstrom, c similar to 12 Angstrom, and beta similar to 97 degrees. The host framework is built up from two structural elements, the tetratitanate-type layer unit of Ti8O184- and the octatitanate-type tunnel one of Ti8O172-, which are stacked in a nearly alternating way along the a axis. Half of the alkali metal ions are accommodated in the layer part and the other half are in the tunnel. This hybrid structure is consistent with the suggestion by Tournoux et al. (Prog. Solid State Chem. 1986, 17, 33). The interlayer cations are reactive, participating in reversible hydration and ion-exchange, while the tunnel ones are inert. The hybrid compound was unstable at elevated temperatures where it was disproportionated into thermodynamically stable titanates. Mixed valent derivatives, A(x)M(6)Ti(16)O(35) (A = Li, K; 0.5 < x < 1.5), were obtained by reductive intercalation of K and Li via the action of K metal vapor and n-butyllithium, respectively.