| Abstract: | Time and Temperature Resolved in situ X-Ray Powder Diffractometry. The Reaction of (NH4)2SnF6 with Ammonia The thermal decomposition of (NH4)2SnF6 under an atmosphere of ammonia is reported. The complicated reaction paths were illucidated by time and temperature resolved in situ x-ray powder diffractometry. It is shown that this technique is a powerful tool to observe structural changes during reaction. It offers also a valuable access to thermodynamic and kinetic data for solid state and gas phase reactions. (NH4)2SnF6 decomposes under ammonia below room temperature to NH4F and amorphous SnF4 · x NH3. At a temperature of 80°C an intermediate product, (NH4)4SnF8, is formed, which decomposes at 140°C into (NH4)2SnF6 and NH4F. At 250°C (NH4)[Sn(NH3)F5] and Sn(NH3)2F4 are formed. The latter crystallises C-centered monoclinic with lattice constants a = 844.1(5) pm, b = 630.5(3) pm, c = 520.2(3) pm and b? = 114.02(7)°. At 330°C a further decomposition yields SnF2(NH2)2 with a C-centered monoclinic cell and lattice constants a = 1 069(7), b = 325.3(2), c = 504.8(3) pm and b? = 105.83(7)°. Finally above 500°C tin metal is formed. |
