A second metastable form of the title compound, C12H13N3 (systematic name: 4,6-dimethyl-N-phenyl-pyrimidin-2-amine), was isolated from an attempted co-crystallization experiment with meso-erythriol in dimethyl sulfoxide (DMSO). The crystals of form 2 at 120 K are monoclinic, space group P21/n with Z' = 4 compared to the previously reported triclinic form with Z' = 2 [Sun et al. (2011 ▸). Acta Chim. Sin.69, 1909-1914]. The four independent mol-ecules in the asymmetric unit form two discrete dimeric units through a concerted pair of N-H⋯N hydrogen bonds with a graph-set notation of R22(8). The origin of the polymorphic behaviour is revealed in that the conformation of each dimer present in the asymmetric unit of the structure is unique and determined by the rotation of the second mol-ecule in the dimer with respect to the first.
Keywords: crystal structure; hydrogen bonding; polymorphism; pyrimethanil.