Two polymorphs of 2-bis[(2-hydroxyphenylmethylene)amino]methylphenol.

C21H18N2O3, Mr = 346.4, monoclinic, C2/c, a = 17.230 (3), b = 12.322 (2), c = 19.675 (3) A, beta = 121.265 (12) degrees, V = 3571 (2) A3, Z = 8, D chi = 1.289 g cm-3, lambda(Cu K alpha) = 1.54184 A, mu = 6.70 cm-1, F(000) = 1456, T = 296 K, R = 0.039 for 3209 observations (of 3691 unique data); triclinic, P1, a = 7.678 (2), b = 10.822 (2), c = 12.539 (2) A, alpha = 63.34 (2); beta = 74.92 (2); gamma = 84.04 (2) degrees, V = 899.1 (4) A3, Z = 2, D chi = 1.279 g cm-3, lambda(Cu K alpha) = 1.54184 A, mu = 6.65 cm-1, F(000) = 364, T = 299 K, R = 0.036 for 3095 observations (of 3399 unique data). Distances and angles are quite similar in the two structures. There are two strong intramolecular hydrogen bonds between a phenolic oxygen and an imino nitrogen in each structure. The intermolecular hydrogen bonds between two phenolic oxygens are closer in the monoclinic crystal than in the triclinic. This closer packing produces the higher melting point for the monoclinic polymorph.