Transformation of one of two CN groups of o-dicyanobenzene in the presence of cyanoguanidine. Crystal and gas-phase structure of 2-(2′-cyanophenyl)-4,6-diamino-1,3,5-triazine

The transformation of one CN group in o-dicyanobenzene in the presence of cyanoguanidine yielding the melaminium derivative in crystalline form has been performed. In the final step of the closing of 1,3,5-triazined ring both hydrogen atoms of one amine group in cyanoguanidine should be transferred to the CN group. Additionally, it has been stated that due to the steric effect of the triazine ring formed from cyanoguanidine and one of cyano group of o-dicyanobenzene, the transformation process of the second CN group in o-dicyanobenzene in the presence of excess of cyanoguanidine is impossible. The 2-(2′-cyanophenyl)-4,6-diamino-1,3,5-triazine crystallises in the centrosymmetric space group of triclinic system. In the crystal the 2-(2′-cyanophenyl)-4,6-diamino-1,3,5-triazine molecule is non-planar due to the steric effect of triazine and cyano groups. The interaction of polar CN group with the nitrogen atom of triazine ring makes the rotation of one ring in relation to other by 22.1° as shown by the ab initio full optimised molecular orbital calculation performed on isolated molecule that corresponds to the gas-phase geometry. In the crystal the rotation angle is almost two times greater due to the intermolecular interaction and hydrogen bonding system. The molecules related by the inversion center interact via two pairs of almost linear N-H⋯N hydrogen bonds forming chains. The chains via more bent N-H⋯N hydrogen bonds form two-dimensional layers parallel to the (110) plane. The hydrogen bonding system and π-π interactions between the rings are responsible for the arrangement of molecules in the crystal. The molecular orbital calculations and conformational analysis have shown four equivalent minima and two pairs of maximum on the potential energy surface. The highest rotational barrier is almost the half of the hydrogen bond energy.