8-{(E)-[(4-Chloro-phen-yl)imino]-meth-yl}-1,1,7,7-tetra-methyl-1,2,3,5,6,7-hexa-hydro-pyrido[3,2,1-ij]quinolin-9-ol.

The title Schiff base, C23H27ClN2O adopts the phenol-imine tautomeric form, with an intra-molecular O-H⋯N hydrogen bond, which generates an S(6) ring motif. Three C atoms of the heterocyclic moiety of the hexa-hydro-pyrido-quinoline unit, as well as the two methyl groups bonded to one of these C atoms, are disordered over two set of sites, with anoccupancy ratio of 0.740 (4):0.260 (4).

4-Meth-oxy-2-{(E)-[(thio-phen-2-yl)methyl-imino]-meth-yl}phenol.

The title Schiff base, C(13)H(13)NO(2)S, adopts the phenol-imine tautomeric form and reveals an intra-molecular O-H⋯N hydrogen bond involving the hy-droxy group and the imino N atom, forming an S(6) ring. The mol-ecule is highly twisted with respect to the central imine group, which is reflected in the dihedral angle of 67.83 (10)° formed by the thienyl and phenol rings. The crystal packing is characterized by weak C-H⋯O and C-H⋯π inter-actions.

5-Diethyl-amino-2-[(E)-(2,4-dimeth-oxy-phen-yl)imino-meth-yl]phenol.

The title Schiff base, C(19)H(24)N(2)O(3), exists in the crystal structure in the phenol-imine tautomeric form with an intra-molecular O-H⋯N hydrogen bond. The planes of the aromatic rings form a dihedral angle of 36.8 (8)°. The crystal packing is characterized by C-H⋯O hydrogen bonds and π-π stacking inter-actions [centroid-centroid distance = 3.478 (4)Å].

Ethyl 2-[2-(4-hy-droxy-3-meth-oxy-benzyl-idene)hydrazin-1-yl-idene]-3,4-dimethyl-2,3-dihydro-1,3-thia-zole-5-carboxyl-ate.

The title compound, C(16)H(19)N(3)O(4)S, is almost planar, with a dihedral angle of 2.88 (9)° between the mean planes of the benzene and thia-zole rings. The mol-ecule adopts an E conformation about the two C=N bonds, with a C-N-N-C torsion angle of -177.01 (11)°. An intra-molecular C-H⋯O hydrogen bond exists between a thia-zole methyl group and the formic acid ethyl ester carbonyl O atom. In the crystal, mol-ecules are linked by O--H⋯O hydrogen bonds, forming chains propagating along [2-10]. The chains are linked via C-H⋯O hydrogen bonds with R(2) (2)(12) ring motifs, forming sheets lying parallel to (12-2). The sheets are further linked through out-of-plane C-H⋯N hydrogen bonds with R(2) (2)(12) ring motifs and C-H⋯π inter-actions, forming an inter-esting three-dimensional supra-molecular architecture.