4-Amino-2,8-dimethyl-6H-pyrimido[1,2-a][1,3,5]triazin-6-one1

In the title compound, C8H9N5O, the mean planes through the pyrimidine and triazine rings form a dihedral angle of 2.83 (16)°. The amino group adopts a trigonal-planar configuration and forms an intramolecular resonance-assisted N—H⋯O=C hydrogen bond with the carbonyl group. In the crystal, molecules are linked via intermolecular N—H⋯N hydrogen bonds into chains of C 2 2(6)[R 2 2(6)] motif. The molecules form two types of sheet parallel to (201) and (01), respectively.

In the title compound, C 8 H 9 N 5 O, the mean planes through the pyrimidine and triazine rings form a dihedral angle of 2.83 (16) . The amino group adopts a trigonal-planar configuration and forms an intramolecular resonance-assisted N-HÁ Á ÁO C hydrogen bond with the carbonyl group. In the crystal, molecules are linked via intermolecular N-HÁ Á ÁN hydrogen bonds into chains of C 2 2 (6)[R 2 2 (6)] motif. The molecules form two types of sheet parallel to (201) and (201), respectively.

Structure Reports Online
In the crystal, the amino group acts as a hydrogen donor for intermolecular N-H···N hydrogen bonding with the nitrogen atoms N1 and N4 (Fig. 2), thereby forming extended chains with the C 2 2 (6)[R 2 2 (6)] hydrogen bond pattern (Bernstein et al., 1995). The chains are organized in two types of sheets parallel to (201) and (201) planes, respectively.

Experimental
The title compound was prepared by the cyclocondensation of 4-methyl-6-oxo-1,6-dihydropyrimidin-2-yl guanidine with triethyl orthoacetate. The details of the synthesis will be published elsewhere. Single crystals suitable for crystallographic analysis were grown by recrystallization from ethyl acetate.

Refinement
All the H atoms attached to the carbon atoms were constrained in a riding motion approximation [0.95 Å for C aryl -H and 0.98 Å for methyl groups; U iso (H) =1.2U eq (C aryl ) and U iso (H) = 1.5U eq (C methyl )] while the N-bound H atoms were located in a difference map and refined freely. In the absence of significant anomalous scattering effects 706 Friedel pairs have been merged. Fig. 1. The molecular structure of the title compound showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.