IGMH-based research on the intramolecular weak interaction of TKX-50

To further comprehensively study the intramolecular weak interaction of the gaseous TKX-50 molecule, the two conformations of the TKX-50 molecule were analyzed via the Independent Gradient Model based on the Hirshfeld Partition (IGMH) method based on the B3LYP/6-311 g (d,p) level for geometry optimization and for single point energy. The conclusions manifest that the weak interactions between these fragments are mainly composed of hydrogen bonds and van der Waals interactions. From the strength of inter-fragment interactions formed by contributing atomic pairs and their percentage contributions, these H bonds, together with dispersion-dominated weak interactions provided by non-direct facing atomic pairs near these H bonds, dominate the inter-fragment interaction resulting in the stability of the molecular structure. Meanwhile, the weak interactions enclosed by end-atoms of two fragments not only include the contributions provided by inter-fragment atomic pairs of two fragments but also include the contributions provided by intra-fragment atomic pairs of fragment 1. For conformation II, due to the H transfer between fragments, a pair of symmetric H bonds at the corresponding regions are extremely strong to reach the level of covalent bond while the two groups −OH at the other end become looser, resulting in conformation II own lower energy. Differences in inter-fragment interactions between two conformations were essentially brought by the stronger electron-withdrawing ability of atom O than that of atom N.