2-Amino-4-meth-oxy-6-methyl-pyrimidin-1-ium picrate.

In the title salt, C(6)H(10)N(3)O(+)·C(6)H(2)N(3)O(7) (-), the dihedral angle between the mean planes of the benzene and pyridine rings is 3.1 (1)°. In the cation, the meth-oxy 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 inter-action 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.