Three new hydrazinium(1+) fluoro complexes, N2H5AsF6, (N2H5)2ZrF6 and (N2H5)2HfF6, were prepared and characterized by means of chemical analysis, IR and Raman spectroscopy and X-ray powder diffraction. Study of their thermal behaviour via TG, DTG and DTA measurements showed that they decompose in stages; the decomposition of N2H5AsF6 proceeded in two steps, through the intermediate NH4AsF6; (N2H5)2ZrF6. Decomposed in three steps, through (NH4)2ZrF6 and NH4ZrF5. The thermal decomposition of (N2H5)2HfF6 is more complex; in the first step (NH4)2HfF6 with some N2H5HfF5 was obtained, and in the second NH4HfF5. The intermediates were identified by means of chemical analysis and vibrational spectroscopy.