Theoretical studies on the structures, intra- and inter-molecular hydrogen bonding interactions in HNF and HNF–H2O clusters in the gaseous, aqueous and solid phases

Abstract

Hydrazimium nitroformate ([N2H5]+[C(NO2)3]− , HNF) is an ionic oxidiser used in solid propellants. Its properties are easily affected by H2O because of its hygroscopicity. In this article, density functional theory (DFT) and molecular dynamics (MD) were employed to study the isolated HNF molecule and the HNF–H2O cluster in gas phase and in the aqueous solution. Three stable conformations were obtained for HNF in the gas phase and in the aqueous solution, respectively, and each conformation can form several different HNF–H2O clusters. Irrespective of whether it is in gas phase or in solution, intramolecular hydrogen bond interactions and other interactions (e.g. the binding energy, the dispersion energy, the second-order perturbation energy and the energy gap between frontier orbitals) of HNF are weaker in the clusters than in the isolated state. The initial decomposition energy of the cluster is lower than that of the isolated HNF molecule in both gaseous and aqueous phases, while the dissociation processes are the same. Molecular dynamic simulations showed that the clustered H2O elongates and weakens the C–NO2 bond in the solid HNF–H2O cluster compared with that in the solid HNF. H2O reduces and weakens intramolecular N–HΛO bonds too, and O–HΛN is the dominant intermolecular hydrogen bond between HNF and H2O.