3,6-Dimethyl-N 1,N 4-bis(1-phenylethyl)-1,4-dihydro-1,2,4,5-tetrazine-1,4-dicarboxamide

In the title molecule, C22H26N6O2, the central tetrazine ring exhibits a boat conformation, and the two phenyl rings form a dihedral angle of 88.39 (6)°. In the crystal, weak N—H⋯O and C—H⋯O hydrogen bonds link molecules into layers parallel to the ab plane.

In the title molecule, C 22 H 26 N 6 O 2 , the central tetrazine ring exhibits a boat conformation, and the two phenyl rings form a dihedral angle of 88.39 (6) . In the crystal, weak N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link molecules into layers parallel to the ab plane.

Comment
In a continuation of our studies of structure-activity relationships in 1,2,4,5-tetrazine derivatives (Hu et al., 2002(Hu et al., , 2004Rao & Hu, 2005, 2006, we have obtained the title compound (I) as colourless crystalline solid. However, IR, NMR, and MS studies failed to prove whether the substituted groups of the nitrogen are located at the 1,4 or 1,2 positions. The structure was confirmed by single-crystal X-ray diffraction.
In the crystal structure, weak intermolecular N-H···O and C-H···O hydrogen bonds (Table 1) link molecules into layers parallel to ab plane (Fig. 2).

Experimental
The title compound was prepared according to the known procedure (Hu et al., 2004;Sun et al., 2003;Skorianetz et al., 1970Skorianetz et al., , 1971. A solution of the compound in ethanol was concentrated gradually at room temperature to afford colourless blocks (m.p. 414-416 K).

Refinement
H atoms were included in calculated positions and refined using a riding model. H atoms were given isotropic displacement parameters equal to 1.2 (or 1.5 for methyl H atoms) times the equivalent isotropic displacement parameters of their parent atoms, and C-H distances were set to 0.96Å for methyl H atoms, 0.93 Å for phenyl H atoms, and 0.98Å for the remainder H atoms, while N-H distances were set to 0.86 Å. In the absence of any significant anomalous scatterers in the molecule, attempts to confirm the absolute structure by refinement of the Flack parameter in the presence of 1803 sets of Friedel equivalents led to an inconclusive value of 0.2 (9). Therefore, the Friedel pairs were merged before the final refinement. Fig. 1. The molecular structure of (I) shown with 30% probability displacement ellipsoids. 3,6-Dimethyl-N 1 ,N 4 -bis(1-phenylethyl)-1,4-dihydro-1,2,4,5-tetrazine-1,4-dicarboxamide