(E)-N'-(4-Chlorobenzylidene)-, (E)-N'-(4-bromobenzylidene)- and (E)-N'-[4-(diethylamino)benzylidene]- derivatives of 4-hydroxybenzohydrazide.

The 4-chloro- [C(14)H(11)ClN(2)O(2), (I)], 4-bromo- [C(14)H(10)BrN(2)O(2), (II)] and 4-diethylamino- [C(18)H(21)N(3)O(2), (III)] derivatives of benzylidene-4-hydroxybenzohydrazide, all crystallize in the same space group (P2(1)/c), (I) and (II) also being isomorphous. In all three compounds, the conformation about the C=N bond is E. The molecules of (I) and (II) are relatively planar, with dihedral angles between the two benzene rings of 5.75 (12) and 9.81 (17)°, respectively. In (III), however, the same angle is 77.27 (9)°. In the crystal structures of (I) and (II), two-dimensional slab-like networks extending in the a and c directions are formed via N-H···O and O-H···O hydrogen bonds. The molecules stack head-to-tail via π-π interactions involving the aromatic rings [centroid-centroid distance = 3.7622 (14) Å in (I) and 3.8021 (19) Å in (II)]. In (III), undulating two-dimensional networks extending in the b and c directions are formed via N-H···O and O-H···O hydrogen bonds. The molecules stack head-to-head via π-π interactions involving inversion-related benzene rings [centroid-centroid distances = 3.6977 (12) and 3.8368 (11) Å].