Hydrogen-bonding patterns in pyrimethamine tetrafluoroborate.

The title compound [systematic name: 2,4-diamino-5-(4-chlorophenyl)-6-ethylpyrimdinium tetrafluoroborate], C12H14ClN4+·BF4−, is isomorphous with pyrimethamine perchlorate. The pyrimethamine (PMN) molecule is protonated at one of the pyrimidine N atoms. The protonated N atom and 2-amino group of the PMN cation interact with the tetrafluoroborate anion through a pair of N—H...F hydrogen bonds [graph set R22(8)]. The inversion-related PMN cations are linked through a pair of N—H...N hydrogen bonds. In addition to the base pairing, the F atoms bridge the 2-amino and 4-amino groups on either side of the paired bases, resulting in a complementary DADA array. [ABSTRACT FROM AUTHOR]