2-{(E)-[(2Z)-2-(1,2-Dihydrophthalazin-1- ylidene)hydrazinylidene]methyl}phenol

R factor = 0.041; wR factor = 0.117; data-to-parameter ratio = 12.6. The title compound, C15H12N4O, adopts an E conformation with respect to the azomethine bond and crystallizes in its hydrazinylidene tautomeric form. The dihedral angle between the ring systems is 15.98 (7). The phenol O—H group forms an intramolecular O—H N hydrogen bond. In the crystal, pairs of N—H N and C—H O hydrogen bonds link neighbouring molecules into centrosymmetric dimers. These dimers are interconnected by means of three types of – stacking interactions. One, with a centroid–centroid distance of 3.577 (1) A ̊ [interplanar separation = 3.4673 (6) Å], connects adjacent molecules into centrosymmetric dimers. The other two interactions, on the outward facing sides of the dimers, are between phenol rings of neighboring molecules [centroid–centroid separation = 3.7907 (13) A ̊ and interplanar separation = 3.5071 (8) Å], and between phthalazin units [centroid–centroid separation = 3.6001 (12) A ̊ and interplanar separation = 3.4891 (7) Å]. In combination, the – inter-actions lead to the formation of infinite layers with molecules stacked along [011]. These layers are, in turn, connected with neighbouring layers through the N—H N and C—H O hydrogen bonds, yielding a three-dimensional supramolecular architecture. Related literature For biological properties of phthalazine and its derivatives, see: Awadallah et al. (2012); Minami et al. (1985); Zhang et al. (2010); Bian et al. (2013). For applications of 1-phthalazinyl hydrazones in optoelectronics, see: Caruso et al. (2005). For the synthesis of related compounds, see: El-Sherif et al. (2012). For related structures and background references, see: Shafiq et al. (2013)