TIME AND TEMPERATURE RESOLVED IN-SITU X-R AY-POWDER DIFFRACTOMETRY - THE REACTION OF (NH4)(2)SNF6 WITH AMMONIA

The thermal decomposition of (NH4)(2)SnF6 under an atmosphere of ammon ia is reported. The complicated reaction paths were illucidated by tim e and temperature resolved in situ x-ray powder diffractometry. It is shown that this technique is a powerful tool to observe structural cha nges during reaction. It offers also a valuable access to thermodynami c and kinetic data for solid state and gas phase reactions. (NH4)(2)Sn F6 decomposes under ammonia below room temperature to NH4F and amorpho us SnF4 . xNH(3). At a temperature of 80 degrees C an intermediate pro duct, (NH4)(4)SnF8, is formed, which decomposes at 140 degrees C into (NH4)(2)SnF6 and NH4F. At 250 degrees C (NH4)[Sn(NH3)F-5] and Sn(NH3)( 2)F-4 are formed. The latter crystallises C-centered monoclinic with l attice constants a = 844.1(5) pm, b = 630.5(3) pm, c = 520.2(3) pm and beta = 114.02(7)degrees. At 330 degrees C a further decomposition yie lds SnF2(NH2)(2) with a C-centered monoclinic cell and lattice constan ts a = 1069(7), b = 325.3(2), c = 504.8(3) pm and beta = 105.83(7)degr ees. Finally above 500 degrees C tin metal is formed.