Theoretical investigation on the heats of formation and the interactions among the azido groups in polyazidoprismanes C₆H_6-n(N₃)_n (n = 1-6)

A series of polyazidoprismanes, C₆H_6-n(N₃)_n (n = 1-6), has been designed computationally. We have calculated the heats of formation (HOFs) of the title compounds by using density functional theory (DFT) with the 6-31G** basis set. We chose [3]prismane C₆H₆-D_3h as a reference compound in the process of designing isodesmic reactions. The relationship between the HOFs and the molecular structures is discussed. The results have shown that the HOFs of the title compounds gradually increase with increasing number of azido groups. On average, the contribution of one azido group to the heat of formation is about 348.8 and 349.3 kJ/mol at the B3LYP and B3P86 levels, respectively. The relative stabilities of the title compounds are discussed in terms of the calculated HOFs, and the energy gaps between the frontier orbitals. The interactions of the azido groups in these polyazidoprismanes are also discussed. The results have not only shown that these compounds may be used as high-energy-density materials, but also provide some useful information for further investigation.