The reaction of NOF2+SbF6- with an equimolar amount of HN3 in an anhydrous HF solution at -45 degrees C produces N3NOF+SbF6-. When an excess of HN3 is used in this reaction, N7O+SbF6- is formed. However, this compound could not be isolated as a solid and rapidly decomposed in a quantitative manner with N2O evolution to N5+SbF6-. This reaction represents a novel and more convenient synthesis for N5+SbF6- because NOF2+SbF6- is more readily accessible than N2F+SbF6- and the N-5(+) can be labeled in all five positions with N-15 by the simple use of terminally singly labeled N-3(-). The formation of the N7O+ cation was established by isotopic labeling experiments and theoretical calculations. It is shown that the addition of a second azido ligand to the same central atom allows the attack of the negatively charged N alpha atom of one ligand by the positively charged N gamma atom of the second ligand, thereby greatly lowering the activation energy barrier toward decomposition and explaining why geminal diazides are much less stable than either monoazides or vicinal diazides.