SYNTHESIS AND X-RAY-POWDER STRUCTURES OF 3 NOVEL TITANIUM PHOSPHATE-COMPOUNDS

Three titanium phosphate porous compounds were prepared hydrothermally and their structures solved from their X-ray powder diffraction patte rns collected on a laboratory X-ray source. The compound, [Ti-3(PO4)(4 )(H2O)(2)]. NH3 (1), crystallizes in triclinic symmetry with a=8.2506( 4), b=8.7879(4), c=5.1022(2) Angstrom; alpha=90.703(1), beta=91.083(1) , gamma=110.158(1)degrees; space group P (1) over bar, and Z=1. The st ructure was solved ab initio by direct methods and refined by Rietveld methods. The structure consists of two octahedrally coordinated titan ium atoms, one of which is bound only by phosphate oxygens and the oth er by phosphate oxygens and water molecules. The bridging of titanium atoms by phosphate oxygens creates a framework consisting of one-dimen sional channels oriented along the c-axis. The ammonia molecules are l ocated in these channels. Compound (2), [Ti2O(PO4)(2)(H2O)(2)], also c rystallizes in the triclinic space group P (1) over bar with a=8.818(1 ), b=9.654(1), c=5.109(1) Angstrom; alpha=93.818(2), beta=93.665(3), g amma=73.313(3)degrees; and Z=2. The complete structure was solved by d irect methods. The two independent titanium atoms are bridged by an ox ygen atom. The remaining coordination sites of the octahedra are compl eted by phosphate oxygens and water oxygen atoms. As in the case of co mpound (1) the water molecules are coordinated to only one type of Ti atom. The structure consists of one-dimensional channels into which th e water oxygens are projected. The compound (NH4)(2)[(Ti3O2) (HPO4)(2) (PO4)(2)] (3) crystallizes in the noncentric space group P2(1), with a =8.5165(3), b=16.7331(5), c=5.1813(2) Angstrom; beta=91.173(2)degrees; and Z=2. A partial structural model was obtained from direct methods procedures and the structure was completed by Fourier methods followin g Rietveld refinement of the full pattern. In this case there are thre e independent titanium atoms and they are bridged by oxygen atoms of t he Ti3O2 group. All the Ti atoms are octahedrally coordinated. As in t he case of compounds (1) and (2), compound (3) forms a framework struc ture containing one-dimensional channels. The hydroxyl groups of the m onohydrogen phosphate and the ammonium cations are located in the chan nels. In the channel the Ti-PO4 framework and the hydroxyl groups crea te cavities around the ammonium cations which block its exchange with other cationic species. (C) 1997 Academic Press.