A redetermination from the original data of the crystal structure of 2-amino-4,6-di-meth-oxy-pyrimidin-1-ium 4-amino-benzoate.

The title structure, C6H9.5N3O2 (0.5+)·C7H6.5NO2 (0.5-), which might be named schematically as 2-amino-4,6-di-meth-oxy-pyrimidine-(μ2-hydrogen)-4-amino-benzoate to indicate a bridging H atom, has been redetermined from the data published by Thanigaimani, Mu-thiah & Lynch [Acta Cryst. (2006), E62, o2976-o2978]. The improvement of the present redetermination consists in a released geometry of the primary amine groups, which were originally assumed to be planar, as well as in a redetermination of the position of the hy-droxy H atom. This H atom, whose parameters were originally constrained, turns out to be situated about the centre of the O⋯N hydrogen bond in two disordered positions with occupancies of 0.5 each.