Synthesis, structure and characterisation of two 2,4-diamino-6-R-1,3,5-triazine derivatives (R=3-cyanophenyl and 4-cyanophenyl)

Two triazine derivatives, 2,4-diamino-6-(3′-cyanophenyl)-1,3,5-triazine (1) and 2,4-diamino-6-(4′-cyanophenyl)-1,3,5-triazine (2), in the crystalline form by addition of cyanoguanidine to the 1,3- and 1,4-dicyanobenzene have been obtained. In both cases the addition of cyanoguanidine to the CN group of dicyanobenzene isomers and formation the triazine ring needs migration of both hydrogens from one amine group of cyanoguanidine to its cyano group. In the final step of the 1,3,5-triazine ring closing reaction, the CN group of dicyanobenzene contributes in the migration of hydrogen from one amine group to the cyano group of cyanoguanidine. The addition of cyanoguanidine molecule, in both cases (1,3-dicyanobenzene and 1,4-dicyanobenzene), takes place only when one of two CN groups of dicyanobenzene is incorporated into triazine ring. Both triazine derivatives crystallise in the monoclinic system in the space group of P21/c (1) and C2/c (2). In the crystal the molecules are not planar, but due to small rotations about the C-C bond the cyanophenyl and the 1,3,5-triazine rings are inclined by 3.4(1) and 17.3(1)° in 1 and 2, respectively. Meanwhile, the geometries of isolated molecules 1 and 2, both are planar, when optimised theoretically. Thus in the crystal the rotation of one ring in relation to other results from the intermolecular interactions like hydrogen bonds, π-π interactions between the aromatic rings and the crystal packing forces. The rotation barrier for the rings rotation around the inter-rings C-C bond is ∼28.4 and ∼27.7 kJ/mol for (1) and (2), respectively.