Synthesis, characterization and acid-base catalytic properties of ammonium-containing tin(ll) phosphates: [NH4][Sn4P3O12] and [NH4] [SnPO4]

Two new tin(II) phosphate materials, three-dimensional [NH4][Sn-4(PO4)(3)] (compound I) and layered [NH4][SnPO4] (compound II), have been synthesized hydrothermally and their structures determined by single crystal X-ray diff raction. Both structures are made of pyramidal SnO3 and tetrahedral PO4 moi eties and have the ammonium ion as the charge balancing species. Compound I is hexagonal: space group P6(3) (#173), a=9.6975(3) and c=8.0938(3) Angstr om; V=659.18(4) Angstrom(3), Z=6. The three-dimensional structure of I invo lves 6-, 8- and 12-membered rings. One-dimensional six-point star (SPS) cha nnels of diameter 5.1 Angstrom occur along the c axis, in addition to tortu ous narrower channel. Ammonium ions occupy the SPS channels and are hydroge n bonded to the framework oxygens. Compound II is monoclinic: space group P 2(1)/c (#14), a=6.5200(13), b=9.4794(19), c =8.0719(16) Angstrom and beta = 90.95(3)degrees; V=498.82(17) Angstrom(3), Z=4. The layered structure is m ade of 4- and 8-membered rings which extend through the be plane and these negatively charged layers are held together by the ammonium ions. Temperatu re-dependent X-ray diffraction studies on I from room temperature up to 800 degrees C reveal the presence of three different phases. Preliminary resul ts on the decomposition of 2-propanol over (I) treated at different tempera tures have yielded insight into the acid-base properties of this novel mate rial and their dependence upon activation conditions. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.