Experimental and Theoretical Charge Density Study on Di-2-pyrazylamine (Hdpza) Molecule in Crystal

Abstract

Electron density distribution of Di-2-pyrazylamine (Hdpza) is studied both by single-crystal X-ray diffraction method at 100K and theoretical calculation. Structural determination reveals that Hdpza molecules crystalize in a syn-anti conformation with an intramolecular C-H...N hydrogen bond between two pyrazine rings and then gather together via two intermolecular N - H - N and C - H - N hydrogen interaction and π - π stacking interaction between pyrazine rings. Charge density analysis is made in terms of deformation density (Δπ), Laplacian distribution and topological analysis of total electron density based on multipole model and theoretical calculation. The agreement between experiment and theory is good. The topological properties at bond critical points of C - C and C - N bonds reveal a covalent bond character, and those of intermolecular interactions, such as hydrogen bonds and π - π stacking interactions, reveal a closed-shell interaction. The potential energy curve of Hdpza molecule shows that the syn-anti conformation is the most stable one (global minima) than the other two of syn-syn and anti-anti conformations. Di-2-pyrazylamine (Hdpza) is a molecule similar to 2,2'-bipyridyl amine, which can exists in three molecular structures - syn-syn, anti-anti and syn-anti forms. The syn-anti form is the most stable molecular structure in the global minma, and the others are in the local minima of potential energy well.