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

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 (ON)CC(NH)HN⋯CpMCH complexes, which exhibit both σ-donor and π-acceptor features, the situation is different concerning the (HN)CC(NO)(O)NO⋯CpMCH complexes, where both charge transfers correspond to the σ-donation. The two charge transfers reinforce each other, resulting in increased stability for (HN)CC(NO)(O)NO⋯CpMCH. This seems to strengthen the (HN)CC(NO)(O)NO⋯M={Ti,Zr,Hf} bond, which may explain the high stability of (HN)CC(NO)(O)NO⋯CpMCH compared to (ON)CC(NH)-HN⋯CpMCH. Results from topological analysis revealed that the decreased sensitivity to decomposition of CNO 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 CNO is more favourable than that with CNH, this specific action on the trigger bond may support the use of Metallocene Methyl Cations (MMC) as possible neutralisers.