Theoretical insight into the acidity and cooperativity effect of the LLM-105∙(HNO3)2 system.

Abstract

In order to reveal the nature of the acidity in explosive product, the acidities and cooperativity effects from the intermolecular H-bonding interactions in the LLM-105∙∙∙(HNO3)2 ternary systems were investigated at the B3LYP/6-311 + + G** and M062X/6-311 + + G** levels, with the integral equation formalism polarized continuum model (IEFPCM) based on the self-consistent-reaction-field. The results show that for the ternary systems, the intermolecular H-bonding interactions are stronger than those in the binary complexes, resulting in the lower [H+] concentrations and larger pKa1 values upon the ternary-complex formations. However, there is no obvious correlation between the acidities and cooperativity effects or APT charges of the H atoms involving the H-bonds. Surface electrostatic potential (ESP) and reduced density gradient are used to reveal the nature of the H-bond and acidity. Interestingly, the acidity is closely related to the ESPs of the H atom (VS,H) involving the intermolecular H-bond, but not to the statistical quantities. This is mainly because both acidity and VS,H are the local properties of system, whereas the cooperativity and statistical quantity of ESP are the global property.