Different packing in three polymorphs of 2,4,6-trimethoxy-1,3,5-triazine.

2,4,6-Trimethoxy-1,3,5-triazine was found to exhibit three different polymorphs. The α-polymorph undergoes reversible phase transformation to the β-polymorph at 340K with an enthalpy of 3.9 kJ mol -1 . The heat of fusion of the β-polymorph at 404K is 18.1 kJ mol -1 . The low-tempreature phase (α-polymorph) crystallizes in the orthorhombic space group Pnma. The high-tempreature phase (β-polymorph) can be obtained from the melt and cystallizes in the monoclinic space group P2 1 . The γ-polymorph is obtained by crystallization from a 1:1 mixture of methanol and methylenechloride from hydrolyzed 2,4-dimethoxy-6-oxybenzophenone-1,3,5-triazine. The γ-polymorph melts at 409K with an enthalpy of 11.4 kJ mol -1 . The γ-polymorph crystallizes in the trigonal space group R3c. The molecules occupy a crystallographic threefold axis. Molecules of 2,4,6-trimethoxy-1,3,5-triazine are planar in all three polymorphs. The major difference between the three polymorphs is the mode of packing of the molecules in the crystal.