The effect of {O,N}=X⋯M={Ti,Zr,Hf} interactions on the sensitivity of C–NO2 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)2C[dbnd]C(NH2)–H2N⋯Cp2MCH3 + complexes, which exhibit both σ-donor and π-acceptor features, the situation is different concerning the (H2N)2C[dbnd]C(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)2C[dbnd]C(NO2)–(O)NO⋯Cp2 MCH3 +. This seems to strengthen the (H2N)2C[dbnd]C(NO2)–(O)NO⋯M={Ti,Zr,Hf} bond, which may explain the high stability of (H2N)2C[dbnd]C(NO2)–(O)NO⋯Cp2MCH3 + compared to (O2N)2C[dbnd]C(NH2)-H2N⋯Cp2MCH3 +. Results from topological analysis revealed that the decreased sensitivity to decomposition of C–NO2 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 C–NO2 is more favourable than that with C–NH2, this specific action on the trigger bond may support the use of Metallocene Methyl Cations (MMC) as possible neutralisers. © 2023