Synthesis and properties of N7O+.

The reaction of NOF(2)(+)SbF(6)(-) with an equimolar amount of HN(3) in an anhydrous HF solution at -45 degrees C produces N(3)NOF(+)SbF(6)(-). When an excess of HN(3) is used in this reaction, N(7)O(+)SbF(6)(-) is formed. However, this compound could not be isolated as a solid and rapidly decomposed in a quantitative manner with N(2)O evolution to N(5)(+)SbF(6)(-). This reaction represents a novel and more convenient synthesis for N(5)(+)SbF(6)(-) because NOF(2)(+)SbF(6)(-) is more readily accessible than N(2)F(+)SbF(6)(-) and the N(5)(+) can be labeled in all five positions with (15)N by the simple use of terminally singly labeled N(3)(-). The formation of the N(7)O(+) 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 Nalpha atom of one ligand by the positively charged Ngamma 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.