Ab initio study on the intermolecular interactions between 1,1-diamino-2,2-dinitroethylene and acetylene: Pull effect on complex formation

The (1:1) complexes of 1,1-diamino-2,2-dinitroethylene (FOX-7) with acetylene were studied computationally. The structure of the complexes, energies and the vibrational frequencies were computed at the HF and B3LYP levels of theory using 6-31G**, 6-311G**, 6-31++G** and 6-311++G** basis sets. The 1A type structure is most stable structure corresponding to N–H⋯π complex of FOX-7-acetylene. The ZPE + BSSE corrected binding energy for 1A is predicted to be −2.01 kcal/mol at the B3LYP/6-311++G** level. To understand the pull effect on complex formation, the most stable 1A type structure were searched in 1,1-diamino-2-nitroethylene (DANE)-acetylene and 1,1-diaminoethylene (DAE)-acetylene complexes using HF and B3LYP levels using a 6-311++G** basis set. The 1E structure of DANE-acetylene complex is quite similar to the most stable structure of FOX-7-acetylene (1A). The absence of electron-withdrawing nitro groups in DAE results in the transformation of the structure, which makes the absence of N–H⋯π hydrogen bond in DAE(1)-acetylene. AIM analysis was also performed to understand the nature of the interactions in these complexes.