The heats of formation of diazene, hydrazine, N2H3+, N2H5+, N2H, and N2H3 and the methyl derivatives CH3NNH, CH3NNCH3, and CH3HNNHCH3

The heats of formation of N(2)H, diazene (cis- and trans-N(2)H(2)), N(2)H(3), and hydrazine (N(2)H(4)), as well as their protonated species (diazenium, N(2)H(3)(+), and hydrazinium, N(2)H(5)(+)), have been calculated by using high level electronic structure theory. Energies were calculated by using coupled cluster theory with a perturbative treatment of the triple excitations (CCSD(T)) and employing augmented correlation consistent basis sets (aug-cc-pVnZ) up to quintuple-zeta, to perform a complete basis set extrapolation for the energy. Geometries were optimized at the CCSD(T) level with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. Core-valence and scalar relativistic corrections were included, as well as scaled zero point energies. We find the following heats of formation (kcal/ mol) at 0 (298) K: Delta H(f)(N(2)H) = 60.8 (60.1); Delta H(f)(cis-N(2)H(2)) = 54.9 (53.2); Delta H(f)(trans-N(2)H(2)) = 49.9 (48.1) versus >= 48.8 +/- 0.5 (exptl, 0 K); Delta H(f)(N(2)H(4)) = 26.6 (23.1) versus 22.8 +/- 0.2 (exptl, 298 K); Delta H(f)(N(2)H(3)) = 56.2 (53.6); Delta H(f)(N(2)H(3)(+)) = 231.6 (228.9); and Delta Hf(N(2)H(5)(+)) = 187.1 (182.7). In addition, we calculated the heats of formation of CH(3)NH(2), CH(3)NNH, and CH(3)HNNHCH(3) by using isodesmic reactions and at the G3(MP2) level. The calculated results for the hydrogenation reaction RNNR + H(2) -> RHNNHR show that substitution of an organic substituent for H improved the energetics, suggesting that these types of compounds may be possible to use in a chemical hydrogen storage system.