Density Functional Theory Studies on the Intermolecular Interactions of Five Aza-calix[6]arene Host with HMX

Five fully optimized structures of complexes between aza-calix[6]arene host monomers (M-a similar to M-e) and complexes (a similar to e) have been obtained at the B3LYP/6-31G(d) level. Natural bond orbital (NBO) analysis was performed to reveal the origin of the interaction. The intermolecular interaction energy was evaluated with basis set superposition error correction (BSSE) and zero point energy correction (ZPEC). The B3LYP/6-31G(d) calculations on the five complexes have shown that the greatest interaction (-13.98 kJ/mol) is found in the complex between HMX and hexa-aza-calix[3]-p-tri-arene[3]-2-amido-1,3,5-tri-azine. The results have indicated that intermolecular interaction energies of aza-calix[6]arenes with substituted group are stronger than those without substituted group, and those with amido are greater than with nitryl. Thus, hexa-azacalix[3]-p-tri-arene[3]-2-amido-1,3,5-tri-azine is rather equal to eliminate HMX from explosive waste water.