Ab initio molecular orbital theory has been used to calculate accurate enthalpies of formationand adiabatic electron affinities or ionization potentials for N
3, N
3-, N
5+, and N
5- from total atomizationenergies. The calculated heats of formation of the gas-phase molecules/ions at 0 K are
Hf(N
3(
2![](/images/gifchars/Pi.gif)
)) =109.2,
Hf(N
3-(
1
+)) = 47.4,
Hf(N
5-(
1A
1')) = 62.3, and
Hf(N
5+(
1A
1)) = 353.3 kcal/mol with an estimatederror bar of ±1 kcal/mol. For comparison purposes, the error in the calculated bond energy for N
2 is 0.72kcal/mol. Born-Haber cycle calculations, using estimated lattice energies and the adiabatic ionizationpotentials of the anions and electron affinities of the cations, enable reliable stability predictions for thehypothetical N
5+N
3- and N
5+N
5- salts. The calculations show that neither salt can be stabilized and thatboth should decompose spontaneously into N
3 radicals and N
2. This conclusion was experimentallyconfirmed for the N
5+N
3- salt by low-temperature metathetical reactions between N
5SbF
6 and alkali metalazides in different solvents, resulting in violent reactions with spontaneous nitrogen evolution. It isemphasized that one needs to use adiabatic ionization potentials and electron affinities instead of verticalpotentials and affinities for salt stability predictions when the formed radicals are not vibrationally stable.This is the case for the N
5 radicals where the energy difference between vertical and adiabatic potentialsamounts to about 100 kcal/mol per N
5.