2-Amino-4-methoxy-6-methylpyrimidin-1-ium picrate

In the title salt, C6H10N3O+·C6H2N3O7 −, the dihedral angle between the mean planes of the benzene and pyridine rings is 3.1 (1)°. In the cation, the methoxy group is almost coplanar with the pyridine ring [C—O—C—N = −0.6 (2)°]. The p-nitro [C—C—N—O = −1.17 (19)°] and one o-nitro [C—C—N—O = 1.83 (19)°] group in the anion are essentially coplanar with the benzene ring. The other disordered o-nitro group containing the major occupancy [0.868 (6)] O atom is twisted −29.0 (2)° from the mean plane of the benzene ring. A bifurcated N—H⋯(O.O) hydrogen bond and weak C—H⋯O intermolecular interaction between the cation and anion produce a network of infinite O—H⋯O—H⋯O—H chains along the c axis in the [101] plane which helps to establish crystal packing. Comparison to a DFT computational calculation indicates that significant conformational changes occur in the free state.

In the title salt, C 6 H 10 N 3 O + ÁC 6 H 2 N 3 O 7 À , the dihedral angle between the mean planes of the benzene and pyridine rings is 3.1 (1) . In the cation, the methoxy group is almost coplanar with the pyridine ring [C-O-C-N = À0.6 (2) ]. The p-nitro  [101] plane which helps to establish crystal packing. Comparison to a DFT computational calculation indicates that significant conformational changes occur in the free state.

Comment
The synthesis of imidazo[1,2-a]pyrimidines has been widely investigated and is one of the most common strategies in the use of 2-aminopyrimidine as the starting material (Katritzky et al., 2003). Recently, the hydrogen-bonding patterns in 2-amino-4,6-dimethylpyrimidinium picrate has been reported (Subashini et al., 2006). In continuation of our work on picrates of biologically important molecules, we have prepared a new picrate of 2-amino-4-methoxy-6-methylpyrimidine, [C 6 H 10 N 3 O] + , [C 6 H 2 N 3 O 7 ]and its crystal structure is reported. A density functional theory (DFT) geometry optimization molecular orbital calculation (Schmidt & Polik, 2007) was performed on the independent cation-anion pair (C 6 H 10 N 3 O + , C 6 H 2 N 3 O 7 -) within the asymmetric unit with the B3LYP 6-31-G(d) basis set (Hehre et al., 1986). Starting geometries were taken from X-ray refinement data. The dihedral angle between the mean planes of the benzene and pyridine rings increases to 28.10°. In the anion, the mean planes of the two o-nitro groups become twisted by 23.14° and 24.20°, respectively, from the mean plane of the benzene ring. The mean plane of the p-nitro group remains planar to the benzene ring. The mean plane of the methoxy group in the cation also remains planar to the pyridine ring. These observations suggest that the bifurcated N-H···(O,O) donor and acceptor hydrogen bonds and weak C-H···O intermolecular interactions play a significant role in crystal stability. Figures Fig. 1

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (