5 10 15 20 25 30 35 40 2θ / ° Intensity Ab initio structure determination of layered sodium titanium silicate containing edge-sharing titanate chains (AM-4) Na 3 (Na,H)Ti 2 O 2 [Si 2 O 6 ]·2.2H 2 O M. S. Dadachov, a J. Rocha, b A. Ferreira, b Z. Lin b and M. W. Anderson* c a Materials Division, Australian Nuclear Science and Technology Organisation, PMB 1 Menai NSW 2234, Australia b Department of Chemistry, University of Aveiro, 3810 Aveiro, Portugal c Department of Chemistry, UMIST, PO Box 88, Manchester, UK M60 1QD The synthesis of a novel layered sodium titanosilicate, Na 3 (Na,H)Ti 2 O 2 [Si 2 O 6 ] 2 .H 2 O (AM-4), and the solution of its crystal structure by ab initio methods are reported. Mixed framework minerals and synthetic compounds with structures built from common polyhedral units (octahedra and tetrahedra sharing all oxygens with at least two other neighbour- ing polyhedra) are of great interest, particularly with respect to host–guest chemistry, structural diversity, ion-exchange and adsorption properties, and shape selective catalysis. The large class of titanium silicates encompasses more than 70 minerals, mainly with mixed cation frameworks. During the last decade ynthetic inorganic and materials chemists have attempted to prepare titanium silicates by using high-temperature solid state ceramic and hydrothermal methods. Recently, we have reported the synthesis of analogues of minerals nenadkevichite, 1 umbite, narsarsukite 2 and penkvilksite. 3,4 We have also solved the structures of the important microporous material ETS-10, 5 as well as rhombohedrally distorted Na 4 [Ti 4 O 4 (SiO 4 ) 3 ] 6 ·H 2 O. 6 Here, we wish to report the synthesis and structure determina- tion of a novel titanium silicate layered compound, monoclinic Na 3 (Na,H)Ti 2 O 2 [Si 2 O 6 ] 2 ·2H 2 O. In a typical AM-4 synthesis, an alkaline solution was prepared by mixing 27.04 g sodium silicate solution (27% m/m SiO 2 , 8% m/m Na 2 O, Merck), 14.76 g NaOH (EKA Nobel) and 38.46 g H 2 O. To this 40.30 g of TiCl 3 (15% m/m solution of TiCl 3 in 10% m/m HCl, Merck) were added and stirred thoroughly. The gel, with a composition 5.6 Na 2 O : 3.1 SiO 2 :1 TiO 2 : 123 H 2 O, was autoclaved at 230 °C under autogeneous pressure for 4 d. The Teflon-lined autoclaves were then quenched in cold water. The crystals, obtained in 80% yield, were filtered off, washed at room temp. with distilled water and dried overnight at 100 °C. Thermogravimetry (TGA-50 Shimadzu analyzer) gives a total mass loss between 20 and 500 °C of ca. 7.4%. The crystal morphology and elemental analysis of crystals were studied on a JEOL JSM-6400 (SEM) and JEOL 2000FX (TEM). The sample studied has an Na : Ti : Si composition ratio of ca. 2 : 1 : 2. Diffraction data were collected with a Siemens D500 powder diffractometer using Co-Ka X-radiation (1.799 Å). Intensity data for h, k, l were collected by the step counting method (step 0.01° and time 30 s) in the range 2q 5–100°. X-Ray diffraction pattern autoindexing was performed with the PROSZKI package 7 from the well resolved first 40 lines with an absolute error of 0.02 (2q) on peak positions. A monoclinic cell swas indicated by the DICVOL 8 and POWDER 9 indexing programs with high figures of merit. Since different programs employing various indexing strategies yielded the same results, the unit cell parameters obtained were taken as correct and were refined with a non-peak weighting scheme by APPELMAN 10 which yielded a = 5.19(3), b = 8.59(5), c = 29.35(5) Å and b = 89.40(2)°. The space group A2/a (no. 15) was unambigu- ously determined from systematic absences: k + l = 2n (hkl) and h + l = 2n (h0l). Peak intensities were altered by changing the method of sample preparation indicating the occurrence of preferred orientation effects. Scanning electron microscopic observations of crystal morphology showed that the crystalline material consists of 10–15 mm platelet single crystals likely to produce orientation effects. In order to reduce preferred orientation effects the side-loading technique was used. The program EXTRA 11 was used to extract structure factor amplitudes of 439 reflections occurring in the 2q interval measured by the LeBail method. 12 At this stage, the following refined unit cell parameters were obtained: a = 5.187, b = 8.582, c = 29.239 Å and b = 89.49°. In the absence of heavy atoms, the crystal structure was solved by direct methods using the program SIRPOW optimised for powder data. 13 Structure factors of 254 (excluding the first and several other high-angle overlappings) reflections were used. The solution of the crystal structure was performed in absence of reliable data on the chemical composition of the compound, its density and unit cell contents. This resulted in the Table 1 Atomic coordinates and isotropic thermal parameters for Na 3 (Na,H)Ti 2 O 2 [Si 2 O 6 ] 2 ·2H 2 O Atom Site x y z B/Å 2 Ti 8f 0.580(3) 0.4127(5) 0.1686(4) 0.5 Na(1) 8f 0.113(5) 0.193(2) 0.1649(9) 1.6 Na(2) 4e 3/4 0.357(5) 0 2.5 Na(3) 4e 1/4 0.037(6) 0 1.6 Si(1) 8f 0.241(1) 0.414(1) 0.2705(6) 0.6 Si(2) 8f 0.597(5) 0.108(1) 0.0928(7) 0.7 O(1) 8f 0.538(7) 20.031(8) 0.2085(8) 0.8 O(2) 8f 0.723(9) 0.260(2) 0.2108(10) 0.8 O(3) 8f 0.516(5) 0.254(3) 0.1257(10) 0.8 O(4) 8f 0.547(6) 0.117(4) 0.0392(7) 0.8 O(5) 8f 0.922(4) 0.393(2) 0.1523(8) 0.8 O(6) 8f 0.878(6) 0.029(5) 0.1055(7) 0.8 O(7) 8f 0.280(6) 0.460(4) 0.2172(5) 0.8 Ow 8f 0.052(5) 0.407(2) 0.05223(11) 2.5 Fig. 1 X-Ray diffraction pattern of AM-4 recorded with Cu-Ka radiation (this was not the data used for structure refinement which was recorded with Co-Ka radiation) Chem. Commun., 1997 2371