2-[4-Phenyl-5-(2-pyridyl)-4H-1,2,4-triazol-3-yl]nicotinic acid: a case of solvent-dependent polymorphism.

The title compound, C(19)H(13)N(5)O(2), crystallizes in two monoclinic forms depending on the solvent used. From methanol or acetone, a yellow form [(Ia), m.p. 533 K] in the space group P2(1) is obtained, while with ethanol as the solvent, an orange form [(Ib), m.p. 541 K] in the space group Cc results. The conformers observed in the two polymorphs differ primarily in the relative orientation of pyridine/phenyl and triazole rings. Molecules of both polymorphs form chains through carboxyl O-H...N hydrogen bonding; however, in each crystal structure, a different group acts as acceptor, viz. a triazole and a pyridyl N atom for (Ia) and (Ib), respectively. This is the first case of polymorphism observed for crystals of a 3,4,5-trisubstituted 1,2,4-triazole derivative.