Crystal and molecular structure of hexamethylmelamine [2,4,6-tris(dimethylamino)-1,3,5-triazine]

Abstract

Crystals of the title compound are hexagonal, a= 9·99 ± 0·01, c= 7·11 ± 0·01 Å, space group P6₃/m, Z= 2. The atomic positions have been determined by least-squares refinement from diffractometer data, the final R being 0·073 for 255 reflexions. The molecule is planar (apart from the hydrogen atoms). It occupies a crystallographic site of symmetry 3/m(, C_3h) but within experimental error the molecular symmetry is 2m(D_3h). Mean bond lengths corrected for molecular oscillations are: C–N(cyclic) 1·345, C–N(exocyclic) 1·366, and C(methyl)-N 1·466 Å. The C–N–C and N–C–N angles in the ring are 112·7 and 127·3°. The atomic thermal vibrations have been analysed to show that at 24 ± 2 °C the molecule is undergoing translational vibrations with root-mean-square amplitudes of 0·25–0·26 Å combined with angular oscillations of root-mean-square amplitude 4·2°. The van der Waals distances between the molecules are normal (3·7–3·8 Å) except in the region of the 6₃ screw axis where the molecules are further apart leaving a channel through the structure with a free diameter of 1·5 Å.