Intra- and Intermolecular Interactions in the Crystals of 3,4-Diamino-1,2,4-triazole and Its 5-Methyl Derivative. Experimental and Theoretical Investigations of Charge Density Distribution

In this paper intra- and intermolecular interactions in crystals of 3,4-diamino-1,2,4-triazole (DAT) and its 5-methyl derivative (DAMT) were investigated in details by experimental (high-resolution X-ray diffraction) and theoretical (ab initio quantum chemistry (MP2/aug-cc-pvdz), AIM, and NBO) methods. Influence of n−π conjugation and n→σ* hyperconjugation on the geometry of DAT and DAMT molecules was shown. All intermolecular interactions in crystals of the DAT and DAMT including weak X–H···π and mixed X–H···N/X–H···π hydrogen bonds were considered. Comparison of BCP characteristics of these interactions from experimental and theoretical charge density distribution demonstrates systematic increase of bonding in isolated dimers compared with dimers in the crystal phase. The ability of amino groups in both crystals serve as proton acceptors in hydrogen bonding was confirmed.