Monocyclic and bicyclic CO₄: how stable are they?

Abstract

Seeking promising molecular species with huge energy release and significant kinetic stability continues to be a hot topic and a great challenge in the field of high-energy density materials (HEDMs). CO 4 is the first high-order carboxide that has the potential as an energetic molecule. However, the intrinsic kinetic stability of its two most studied energy-rich isomers, i.e., 1 1 (monocyclic) and 1 2 (bicyclic), has remained quite unclear in spite of numerous studies. This has greatly hindered the quantitative stability assessment of 1 1 and 1 2 under various conditions as well as the justification of their prospect as energetic candidates. In this work, for the first time we report the rate-determining transition states associated with the CO 2elimination from 1 1 and 1 2. The thermodynamics of 1 1 and 1 2 was described using G3B3, CBS-QB3, G4, W1BD, CCSD(T)/CBS and CASPT2/CBS, while the kinetic stability was analyzed based on brokensymmetry UCCSD(T)/CBS and CASPT2/CBS single-point energy calculations on UB3LYP geometries. The rate-determining barriers for the dissociation of 1 1 and 1 2 into CO 2 + 1 O 2 at 298 K were found to amount to 28.7 and 14.7 kcal mol À1 at the CASPT2(18e,12o)/CBS level of theory, and 23.5 and 21.1 kcal mol À1 at the UCCSD(T)/CBS level of theory, respectively. 1 1 is a kinetically stable energetic molecule, which releases 45.2 kcal mol À1 upon dissociation into CO 2 + 1 O 2 at the CASPT2(18e,12o)/CBS level and 38.9 kcal mol À1 at the UCCSD(T)/CBS level, and could serve as a rigid energetic building block for larger oxocarbons. The bicyclic 1 2 releases much higher energy, 79.3 kcal mol À1 at the CASPT2(18e,12o)/CBS level and 73.4 kcal mol À1 at the CASPT2-corrected UCCSD(T)/CBS level whereas the barrier for dissociation is lower than that of monocyclic 1 1.

Free and Complexed Fluoropentazoles: Anomalous Ring Charge and Appreciable Kinetic Stability

“…It is generally acknowledged that the feasibility of detection of a chemical structure strongly relies on the generation route, characterization technique, and ambient conditions (e.g., temperature and pressure). For example, the exotic and ever elusive CO 4 (bicyclic), N 4 (open chain), and trans -HO 3 (open chain) with low decomposition barriers of approximately 14.7 kcal/mol, 13.1 kcal/mol, and 1.2 kcal/mol have all been detected by neutralization–reionization mass spectrometry (NRMS). − The fluorine-protonated trifluoroammonium cation (HNF 3 + ) with a dissociation barrier of 14.6 kcal/mol to NF 2 + and HF has been detected by mass spectrometry . To the best of our knowledge, numerous Lewis acid adducts (with one or two Lewis acids attached) of simple nitrogen-rich species have been reported in experiments. − , Introducing LA(s) would have two positive effects on cyclo -FN 5 .…”