N 2,N 2′-Bis(2-hydroxybenzylidene)-2,2′-bipyridyl-3,3′-dicarbohydrazide

In the title compound, C26H20N6O4, the two aroylhydrazone side groups exist as diastereomeres, both in the keto form in the crystal structure. The aroylhydrazone units support the molecular conformation through an intramolecular N—H⋯O hydrogen bond. Two molecules are connected into a centrosymmetric dimer by intermolecular N—H⋯N hydrogen bonds. These dimers are connected into chains along the a axis by intermolecular O—H⋯O hydrogen bonds. The combination of these hydrogen bonds results in layers in the bc plane. The layers are further linked by weak C—H⋯π contacts to form a three-dimensional network structure.

In the title compound, C 26 H 20 N 6 O 4 , the two aroylhydrazone side groups exist as diastereomeres, both in the keto form in the crystal structure. The aroylhydrazone units support the molecular conformation through an intramolecular N-HÁ Á ÁO hydrogen bond. Two molecules are connected into a centrosymmetric dimer by intermolecular N-HÁ Á ÁN hydrogen bonds. These dimers are connected into chains along the a axis by intermolecular O-HÁ Á ÁO hydrogen bonds. The combination of these hydrogen bonds results in layers in the bc plane. The layers are further linked by weak C-HÁ Á Á contacts to form a three-dimensional network structure.

Comment
Hydrazones and their metal complexes have gained a special attraction due to their biological activity (Rodriguez-Argüelles et al., 2004;Wiley & Clevenger, 1962). These compounds have also been proposed as chemosensors (Xiang et al., 2006), catalysts (Mino et al., 2001 and nucleophiles (Wood et al., 2004). Hydrazone ligands can coordinate with metal ions to produce stable metal complexes owing to their facile keto-enol tautomerism.
As shown in Fig. 1, two aroylhydrazone units are situated on both sides of the 2,2'-dipyridyl linking group which can decrease the steric hindrance among the pyridyl rings. The two aroylhydrazone side groups exist as diastereomeres, both in the keto form in the crystal structure. The aroylhydrazone units support the molecular conformation through an intramolecular N-H···O hydrogen bond (Table 1).
A pair of intermolecular N-H···N hydrogen bonds connect two adjacent molecules into dimers via inversion centres (Fig.   2). These dimers are connected into chains along a axis by intermolecular O4-H4···O3 hydrogen bonds. The combination of both hydrogen bonds generate layers which extend along the b+c direction (Fig. 3). The layers are linked by weak C-H···π contacts (Table 1) to form a three-dimensional network structure. Cg3 and Cg4 are the centroids of the benzene rings C1-C6 and C21-C26, respectively. There is another intramolecular hydrogen bond, O1-H1···N1, which results from the planar geometry in the H1-O1-C1-C6-C7-N1 ring system (Table 1).

Experimental
A mixture of 2,2'-bipyridyl-3,3'-diformylhydrazide (0.272 g, 1 mmol), salicylaldehyde (2.5 mmol, 0.26 ml) and a drop of glacial acetic acid in ethanol (20 ml) was stirred at reflux temperature for 3 h. The solution was filtered and the filtrate was set aside to be crystallized. Yellow crystals suitable for the X-ray diffraction study were obtained after 5 d.