Hydrogen-bonding patterns in pyrimethaminium dinitrate.

The title compound, 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimidine-1,3-diium dinitrate, C12H15ClN42+.2NO3-, contains two crystallographically independent pyrimethamine (PMN) molecules, which differ in the relative orientations of the pyrimidine and benzene rings and of the ethyl substitutents. In both pyrimethamine molecules, all the pyrimidine N atoms are protonated, unlike most related compounds, in which only one pyrimidine N atom is protonated. The two pyrimethamine moieties are bridged by a variety of N-HO(nitrate) interactions, including some three-centre hydrogen bonds.