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

Two new tin(II) phosphate materials, three-dimensional [NH4][Sn4(PO4)3] (compound I) and layered [NH4][SnPO4] (compound II), have been synthesized hydrothermally and their structures determined by single crystal X-ray diffraction. Both structures are made of pyramidal SnO3 and tetrahedral PO4 moieties and have the ammonium ion as the charge balancing species. Compound I is hexagonal: space group P63 (#173), a=9.6975(3) and c=8.0938(3) Å; V=659.18(4) Å3, Z=6. The three-dimensional structure of I involves 6-, 8- and 12-membered rings. One-dimensional six-point star (SPS) channels of diameter 5.1 Å occur along the c axis, in addition to tortuous narrower channel. Ammonium ions occupy the SPS channels and are hydrogen bonded to the framework oxygens. Compound II is monoclinic: space group P21/c (#14), a=6.5200(13), b=9.4794(19), c=8.0719(16) Å and β=90.95(3)°; V=498.82(17) Å3, Z=4. The layered structure is made of 4- and 8-membered rings which extend through the bc plane and these negatively charged layers are held together by the ammonium ions. Temperature-dependent X-ray diffraction studies on I from room temperature up to 800°C reveal the presence of three different phases. Preliminary results on the decomposition of 2-propanol over (I) treated at different temperatures have yielded insight into the acid–base properties of this novel material and their dependence upon activation conditions.