Catalytic trimerization of 2- and 4-cyanopyridine isomers to the triazine derivatives in presence of magnesium phthalocyanine

The crystals of 2,4,6-tris(2-pyridyl)-1,3,5-triazine and 2,4,6-tris(4-pyridyl)-1,3,5-triazine isomers have been obtained by a catalytic trimerization of 2- and 4-cyanopyridine in presence of magnesium phthalocyanine. For the 2,4,6-tris(2-pyridyl)-1,3,5-triazine isomer there are two possible conformations that differ in the positions of the N atoms in pyridine rings in relation to the triazine ring. These conformations differ by ∼11.30 kJ mol−1 as shown by the molecular orbital calculations. The 2,4,6-tris(2-pyridyl)-1,3,5-triazine crystallises in the centrosymmetric space group of the triclinic system, while the 2,4,6-tris(4-pyridyl)-1,3,5-triazine isomer crystallises in the C2/c space group of monoclinic system. The 2,4,6-tris(2-pyridyl)-1,3,5-triazine molecule is non-planar in the crystal, due to the steric effect of lone-pair electron at the N atom in both pyridine and triazine rings is non-planar. The repulsive interaction between the lone-pair electron is the reason for the rotation of the pyridine rings along the C–C bonds. The pyridine rings in the 2,4,6-tris(4-pyridyl)-1,3,5-triazine molecule are not coplanar with the central triazine ring. The arrangement of molecules in both crystals is mainly determined by the π–π intermolecular interactions. The X-ray geometry of both molecules in the solid-state is compared with the gas-phase geometry obtained by the ab initio molecular orbital calculations.