Refinement of the crystal structure of Na2Ti3O7

The crystals of Na2Ti3O7 were obtained by crystallization from flux. The structure of the compound was refined from X-ray diffraction data collected on a four-circle diffractometer (2theta/theta scanning technique, lambdaMoK(alpha) radiation, graphite monochromator, theta(max) = 40degrees). The crystals are monoclinic a = 9.133(2) Angstrom, b = 3.806(1) Angstrom, c = 8.566(2) Angstrom, beta = 101.57(3)degrees, sp. gr. P2(1)/m, Z = 2, p(calcd) = 3.435 g/cm(3) R = 0.035, 1241 reflections with I greater than or equal to 2sigma(I). The geometric characteristics of the Ti-polyhedra are analyzed as to their positions in the trioctahedral ribbon. The polymorphism of the {Ti3O7}(2-) anionic radical in the structures of Na2Ti3O7 and PbTi3O7 is described. The topology and dimensionality of the {Ti3O7}(2-) anionic radical are demonstrated to depend on the type of the large cations located at the lattice points of the hexagonal close packing characteristic of both structures. (C) 2003 MAIK Nauka/Interperiodica.