Formation of the cyclo-Pentazolate N5- Anion by High-Energy Dissociation of Phenylpentazole Anions

The recent successful preparation of the cyclo- pentazolate N 5 - anion ( cyclo- N 5 - ) by the dissociation of the p -pentazolylphenolate anion using high-energy collisions is accounted for by considering the electronic structure of the system. It is shown that a symmetry-allowed conical intersection is involved, leading directly from an electronically excited state of the precursor to ground-state cyclo- N 5 - . The presence of the conical intersection is manifested by the structure of the thermal transition state of the C−N bond dissociation reaction, which is shown to be bent. A similar mechanism is proposed for the formation of cyclo- N 5 - from the dimethylaminophenylpentazole anion radical. High-level model calculations on the dissociation of these precursors and of the HN 5 •- anion radical, which is the parent molecule of the larger aromatic pentazolates, support the proposed model.