POROUS TITANOSILICATE NANORODS IN THE STRUCTURE OF YUKSPORITE, (SR,BA)2K4(CA,NA)14(δ,MN,FE) {(TI,NB)4(O,OH)4[(SI6O17] 2[SI2O7]3

Abstract

The crystal structure of yuksporite, (Sr,Ba)2K4(Ca,Na)14(□,Mn,Fe){(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3}(H2O,OH)n, where n ~ 3 [monoclinic, P21/m, a = 7.126(3), b = 24.913(6), c = 17.075(7) Å, β = 101.89(3)°, V = 2966.4(17) Å3] has been solved using X-ray synchrotron radiation data collected from a needle-like crystal with dimensions of 6 × 6 × 50 μm3 at the Swiss-Norwegian beamline BM01 of the European Synchrotron Research Facility (ESRF, Grenoble, France). The structure was refined to R1 = 0.101 on the basis of 2359 unique observed reflections with |Fo| ≥ 4σ F. The structure of yuksporite is based upon titanosilicate nanorods elongated along a and with an elliptical cross-section of ca. 16 × 19 Å = 1.6 × 1.9 nm. Silicate tetrahedra form double xonotlite-like chains 1∞[Si6O17] oriented parallel to (001). Two 1∞[Si6O17] chains are linked into a rod via TiO6 octahedra and Si2O7 double tetrahedra. The {(Ti,Nb)4(O,OH)4[Si6O17]2[Si2O7]3} nanorods are porous. The internal pores are defined by eight-membered rings (8MR) with open diameters of 3.2 Å. The interior of the titanosilicate nanorods is occupied by Sr, Ba, K, and Na cations and H2O molecules. The nanorods are separated by walls of Ca coordination polyhedra that are parallel to (010) and link the rods into a three-dimensional structure.