Salts containing the [N 5 ] + and [N 3 ] ions are known (see Section 15.5),

Question:

Salts containing the [N₅]⁺ and [N₃]‾ ions are known (see Section 15.5), but (as of 2016) the ionic salt [N₅]⁺ [N₃]‾ has not been isolated.

(a) Use the VBT approach to estimate the lattice energy of [N₅]⁺[N₃]‾. Data: V (N₅⁺) = 0.051 nm³; V(N₃‾) = 0.058 nm³.

(b) Given that ∆_fHº(298 K) for [N₅]⁺(g) and [N₃]‾ (g) = +1479 and +198 kJ mol⁻¹, respectively, use your answer from part (a) to estimate ∆_fHº(298 K) for [N₅]⁺[N₃]‾,(s). Comment on the value obtained for ∆_fHº([N₅]⁺ [N₃]‾, s) and on any assumptions made. What can you say about the thermodynamic stability of [N₅]+ [N3]‾ (s)?