The effect of {O,N}=X⋯M={Ti,Zr,Hf} interactions on the sensitivity of CNO2 trigger bonds in FOX-7: Approach based on the QTAIM/EDA-NOCV analysis

Abstract

The local chemical reactivity of FOX-7 (1,1-diamino-2,2-nitroethylene, also known as DADNE from DiAminoDiNitroEthylene) was elucidated through a quantitative study of the electrostatic potential on the molecular surface, topological analysis based on Bader's theory, and the EDA-NOCV method. Unlike (O₂N)₂CC(NH₂)H₂N⋯Cp₂MCH₃⁺ complexes, which exhibit both σ-donor and π-acceptor features, the situation is different concerning the (H₂N)₂CC(NO₂)(O)NO⋯Cp₂MCH₃⁺ complexes, where both charge transfers correspond to the σ-donation. The two charge transfers reinforce each other, resulting in increased stability for (H₂N)₂CC(NO₂)(O)NO⋯Cp₂MCH₃⁺. This seems to strengthen the (H₂N)₂CC(NO₂)(O)NO⋯M={Ti,Zr,Hf} bond, which may explain the high stability of (H₂N)₂CC(NO₂)(O)NO⋯Cp₂MCH₃⁺ compared to (O₂N)₂CC(NH₂)-H₂N⋯Cp₂MCH₃⁺. Results from topological analysis revealed that the decreased sensitivity to decomposition of CNO₂ bonds depends on the chemical nature of the interacting metal, and the best achievements are obtained for the Hf-based complex. Our results demonstrate that the interaction of M={Ti,Zr,Hf} with CNO₂ is more favourable than that with CNH₂, this specific action on the trigger bond may support the use of Metallocene Methyl Cations (MMC) as possible neutralisers.

Keywords: ESP/EDA-NOCV/QTAIM analysis; Energetic molecules; FOX-7 or DADNE; Metallocene methyl cations; Sensitivity of trigger bonds.