THE N4 MOLECULE HAS AN OPEN-CHAIN TRIPLET C-2H STRUCTURE

The lowest-energy N4 is computed ab initio to be the planar (C2h(Bu))-B-3 open-chain structure 13. The open-chain N4 singlet-state structures dissociate on geometry optimization. The tetraaza-tetrahedrane T(d) structure 1 and the tetrazete D2h structure 2 are minima at MP2/6-31G*. However, both are higher in energy than 13 (24.1 and 21.2 kcal/mol [UQCISD(T) (full)/6-311+G*//MP2/6-31G*+ ZPE(MP2/6-31G*), respectively]. The energy of 13 is 157.5 kcal/mol higher than that of two N2 (1SIGMA(g)+) molecules [UQCISD(T) (full)/6-311+G*//MP2/6-31G*].