Theoretical Investigation Into The Change Of Sensitivity In Nitrotetrazoles Upon The Formation Of The Intermolecular Interaction

The search of new and thermally stable insensitive explosive has been a primary goal inthe field of energetic material chemistry in order to avoid the catastrophic explosion in useand meet the requirement of military application. It has been extensively shown from manyexperimental and theoretical results that hydrogen bond or introducing cation into thestructure of explosive can lead to a dramatic change of explosive sensitivity. The theoreticalinvestigation on the changes of the bond dissociation energy （BDE） in the X–NO₂（X=C, Nand O） bond upon the formation of the hydrogen-bonded or molecule-cation interactioncomplexes with nitrotetrazole or its methyl derivatives might reveal, in a way, the nature ofthe change of sensitivity. It will be important for keeping, transporting, safe using, moleculardesign and synthesis of the important energetic nitrotetrazole and its methyl derivatives.Research contents as follows:A comparative theoretical investigation on the change in the strength of trigger-bond uponthe formation of the Na+, Mg²⁺and HF complexes involving the nitro group of RNO₂（R=–CH₃,–NH₂,–OCH₃） or the C=C bond of （E）-O₂N–CH=CH–NO₂was carried out using theB3LYP and MP2（full） methods with the6-311++G**,6-311++G（2df,2p） and aug-cc-pVTZbasis sets. Except for the Mg²⁺···π system with （E）-O₂N–CH=CH–NO₂, the strength of thetrigger-bond X–NO₂（X=C, N or O） was enhanced upon complex formation. Furthermore, theincrement of the bond dissociation energy of the X–NO₂bond in the Na+complex was fargreater than that in the corresponding HF system. Thus, the explosive sensitivity in the formermight be lower than that in the latter. For C2H2N2O4···Mg²⁺, the explosive sensitivity might bealso reduced. Therefore, it is possible that introducing cation into the structure of explosivemight be more efficacious to reduce explosive sensitivity than the formation of theintermolecular hydrogen-bonded complex. The analyses of AIM, NBO and electron densityshifts showed that the electron density shifted toward the X–NO₂bond upon complexformation, leading to the strengthened X–NO₂bond and the possibly reduced explosivesensitivity. The changes of bond dissociation energy in the N–NO₂bond and nitro group charge uponthe formation of the intermolecular hydrogen-bonding interaction between HF and the nitrogroup of14kinds of nitrotetrazoles or methyl derivatives were investigated using the B3LYPand MP2（full） methods with the6-311++G**,6-311++G（2df,2p） and aug-cc-pVTZ basis sets.The BDE of the trigger was improved, the strength of the N–NO₂bond was enhanced and thecharge of nitro group turned more negative in complex in comparison with those in isolatednitrotriazole molecule. The increment of the N–NO₂bond dissociation energies correlatedwell with the intermolecular H-bonding interaction energies. Electron density shifts analysesshowed that the electron density shifted toward the N–NO₂bond upon complex formation,leading to the strengthened N–NO₂bond and the possibly reduced explosive sensitivity.The changes of bond dissociation energy （BDE） in the N–NO₂bond and nitro group chargeupon the formation of the molecule-cation interaction between Na+and the nitro group of14kinds of nitrotetrazoles or methyl derivatives were investigated using the B3LYP andMP2（full） methods with the6-311++G**,6-311++G（2df,2p） and aug-cc-pVTZ basis sets.The strength of the N–NO₂bond was enhanced in comparison with that in the isolatednitrotetrazole molecule upon the formation of molecule-cation interaction. The increment ofthe N–NO₂bond dissociation energy （ΔBDE） correlated well with the molecule-cationinteraction energy. Electron density shifts analysis showed that the electron density shiftedtoward the N–NO₂bond upon complex formation, leading to the strengthened N–NO₂bondand the possibly reduced explosive sensitivity.