1,2-Bis(pyridin-4-yl)ethene-4-hy-droxy-3-meth-oxy-benzoic acid (1/1).

In the title 1:1 co-crystal [alternatively called bi-pyridine ethyl-ene- p -vanillic acid (1/1)], C 12 H 10 N 2 ·C 8 H 8 O 4 , the dihedral angle between the pyridine rings is 59.51 (5)°. In the crystal, the mol-ecules are linked by O-H⋯N hydrogen bonds, generating [401] chains of alternating C 12 H 10 N 2 and C 8 H 8 O 4 mol-ecules.