Theoretical study of the pentanitrogen cation (N5+)

Ab initio quantum-chemical calculations have been applied to study the structure, energies and properties of the pentanitrogen cation (N5+) recently prepared experimentally by Christe and co-workers. The cation has an open C2v form and a closed-shell singlet ground state N5s whose calculated vibrational wavenumbers agree well with the observed IR–Raman values. The triplet structure N5t (3A″) corresponds to a weak complex between linear triplet N3+ and N2 and occurs at ∼26 kJ/mol above N5s. In both states, the cyclic structure does not correspond to an energy minimum. The heat of formation is ΔHf, 0(N5+,1A1)=1470±15 kJ/mol. Decomposition of the pentanitrogen cation is endothermic by ∼44 kJ/mol relative to N2+N3+(3Σ−g) and 181 kJ/mol relative to N2+N3+(1Σ+g). The N5 radical also has an open C2v form and its ionization energy is IEa(N5)=7.4±0.2 eV.