THE SYNTHESIS, VIBRATIONAL SPECTRA, CRYSTAL STRUCTURE AND THERMAL DECOMPOSITION OF (N₂H₅)₃AlF₆

A. Rahten, P. Benkiè, A. Jesih
Jožef Stefan Institute, Jamova 39, 1111 Ljubljana, Slovenia

ABSTRACT

(N₂H₅)₃AlF₆ has been synthesized by the reaction of AlF₃.3H2O and N₂H₅F in a water solution. N-N stretching bands of the N₂H₅+ ions appear as medium band at 969 and as strong band at 955 cm-1 in infrared and at 965 and 955 cm-1 in Raman indicating different environments of the environment sensitive N₂H₅+ ions. The compound crystallizes in orthorhombic system, space group P212121 (No.19), with a=9.015(2) A, b=9.191(2) A and c=10.479(2) A. (N₂H₅)₃AlF₆consists of separated AlF₆^-3 octahedra, arranged in a distorted f.c.c. fashion. Octahedra are connected through hydrazinium ions and there are two types of strong hydrogen bonds regarding the orientation of NH2-NH3+ units. (N₂H₅)₃AlF₆decomposes thermally by exothermic decomposition of hydrazinium(+1) ions to yield the mixture of (NH₄)₃AlF₆ and NH₄AlF₄ at 243 oC. Further decomposition leads to NH₄AlF₄at 301 oC and b-AlF₃ at 460 oC. The final decomposition product is a-AlF₃ at 700oC.