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The title molecule, C21H26N2O3, adopts a V-shaped conformation and is chiral at the C atom with methyl group attached at the common cut of the edges of the V-conformation and crystallizes as a racemate. It also contains an intramolecular O—H...N hydrogen bond. In the crystal, N—H...O hydrogen bonds form chains of molecules extending along the c-axis direction, together with normal van der Waals contacts. The roles of the various intermolecular interactions were clarified by Hirshfeld surface analysis, which reveals that the most important contributions to the crystal packing are from H...H (62.6%), C...H/H...C (15.8%) and O...H/H...O (15.3%) contacts.

The conformation about the central benzene ring in the molecule of (I), C20H19N3O2, is partially determined by an intramolecular N—H...O hydrogen bond. In the crystal, chains parallel to the c axis are generated by intermolecular N—H...O hydrogen bonds with the chains assembled into a three-dimensional network structure by intermolecular C—H...O hydrogen bonds and C—H...π(ring) interactions. The molecule of (II), C22H21N3O, differs from (I) only in the substituent at the hydrazide N atom where a phenylmethylene moiety for (II) is present instead of a furanmethylene moiety for (I). Hence, molecules of (I) and (II) show similarities in their molecular and crystal structures. The conformation of the central portion of the molecule of (II) is also therefore partially determined by an intramolecular N—H...O hydrogen bond and intermolecular N—H...O hydrogen bonds form chains parallel to the c axis. Likewise, the chains are connected into a three-dimensional network by C—H...O hydrogen bonds and C—H...π(ring) interactions.

Poor corrosion resistance of mild steel (MS) is a serious concern in many industrial applications. Application of corrosion inhibitors is a possible solution to combat steel corrosion. As yet, there is very little research reported focusing on hydrazone derivatives as corrosion inhibitors, here we present a combined experimental and theoretical study of the adsorption of three newly synthesized hydrazones (HDZs), namely, (E)-N′-(4-(dimethylamino)benzylidene)-2-((2,3-dimethylphenyl)amino)benzohydrazide (HDZ-1), (E)-2-((2,3-dimethylphenyl)amino)-N′-(4-methylbenzylidene)benzohydrazide, (HDZ-2) and (E)-N′-benzylidene-2-((2,3-dimethylphenyl)amino)benzohydrazide (HDZ-3) on the MS surface in 1 M HCl. The interaction of HDZs and the metal surface was investigated using electrochemical techniques, X-ray photoelectron spectroscopy (XPS), DFT and molecular dynamic (MD) simulations. XPS shows that inhibitor molecules form a stable layer on steel surface through chemical and physical interactions. HDZs adsorption onto the steel surface was found to follow Langmuir model. Furthermore, electrochemical measurement results demonstrated that our developed inhibitors act as of mixed-type (anodic and cathodic), with HDZ-1 showing the highest polarization resistance and lowest corrosion current density. Scanning electron microscope (SEM) was used to examine the surface morphology of the steel samples. The new hydrazones showed significantly improved steel corrosion resistance, which provides opportunities to explore the inhibitive activity of structurally similar compounds. Keywords: Mild steel, Corrosion inhibition, HCl, Hydrazone derivative, Modelling studies

The title compound, C24H21N3O3, crystallizes with two unique but closely r.m.s. overlay fit = 0.215 Å) comparable molecules (1 and 2) in the asymmetric unit of the triclinic unit cell. In molecule 1, the dihedral angles between the central imidazlole ring and the benzene-ring substituents are 42.51 (9), 45.41 (9) and 56.92 (8)°, respectively. Comparable data for molecule 2 are 39.36 (10), 34.45 (11) and 60.34 (8)°, respectively. The rings at the 2-positions carry p-nitro substituents that subtend dihedral angles of 12.9 (4)° in molecule 1 and 11.7 (4)° in molecule 2 to their respective benzene ring planes. The imidazole rings also have propan-2-ol substituents on the 1-N atoms, which adopt extended conformations for the N—C—C—C chains. In the crystal, classical O—H...N hydrogen bonds combine with C—H...O, C—H...N and C—H...π(ring) hydrogen bonds and stack the molecules along the a-axis direction.

The title compound, C16H13N3OS, comprises an oxadiazolethione ring bound to the N atom of an almost planar carbazole ring system (r.m.s. deviation = 0.0088 Å) through an ethylene chain. The oxadiazole ring is inclined to the the carbazole ring system by 40.71 (6)°. In the crystal, N—H...O, N—H...S, C—H...N and C—H...S hydrogen bonds combine with C—H...π(ring) and π–π contacts to stack the molecules along the b-axis direction.

The title compound, C24H21ClN2O, crystallizes with two unique molecules in the asymmetric unit. In each molecule, the central imidazole ring is substituted at the 2-, 4- and 5-positions by benzene rings. The 2-substituted ring carries a Cl atom at the 4-position. One of the imidazole N atoms in each molecule has a propan-2-ol substituent. In the crystal, a series of O—H...N, C—H...O and C—H...Cl hydrogen bonds, augmented by several C—H...π(ring) interactions, generate a three-dimensional network of molecules stacked along the a-axis direction.

In the title molecule, C27H25N3O3S·H2O, the dihedral angle between the planes of the thienyl ring and the pendant p-tolyl group is 39.25 (6)°, while that between the pyridine ring and the pendant phenyl ring is 44.37 (6)°. In addition, there is a slight twist in the bicyclic core, with a dihedral angle of 2.39 (4)° between the thienyl and pyridine rings. The conformation of the carbamoyl moiety is partially determined by an intramolecular N—H...O hydrogen bond. In the crystal, complementary N—H...O hydrogen bonds form dimers which are then associated into chains parallel to the c axis through O—H...N hydrogen bonds involving the water molecule of crystallization. Electron density associated with an additional solvent molecule of partial occupancy and disordered about a twofold axis was removed with the SQUEEZE procedure in PLATON [Spek (2015). Acta Cryst. C71, 9–18]. The given chemical formula and other crystal data do not take into account the unknown solvent molecule(s).

In the title compound, C21H22N4O2S, the dihedral angle between the pyrazole ring and adjacent benzene ring is 6.4 (1)°. The molecular conformation is influenced by intramolecular N—H...O and C—H...O hydrogen bonds. In the crystal, N—H...O hydrogen bonds plus C—H...π and π–π stacking interactions form chains extending in the a-axis direction. The chains are linked by complementary pairs of C—H...π interactions.

In the title compound, C22H20ClN3O, the dihedral angle between the planes of the chlorophenyl and dimethylphenyl rings is 66.50 (9)°. These rings make dihedral angles 47.79 (8) and 69.24 (9)°, respectively, with the central benzene ring. In the crystal, molecules are linked into a three-dimensional supramolecular network by N—H...O, C—H...O hydrogen bonds and weak C—H...π interactions.

In the title compound, C23H22ClN3O, the dihedral angle between the planes of the chlorophenyl and dimethylphenyl rings is 62.49 (10)°. These rings make dihedral angles of 21.11 (9) and 59.85 (9)°, respectively, with the central benzene ring. In the crystal, molecules are linked into a three-dimensional supramolecular network by N—H...N, N—H...O and C—H...O hydrogen bonds, and weak C—H...π interactions.

The title molecule, C22H19N3O2, is a new polymorphic modification, viz. the β-phase; the α-phase has been previously published [Liang & Wang (2010). Acta Cryst. E66, o1968–o1969]. In the crystal of the β-phase, the molecules pack in helical chains generated by C—H...O hydrogen bonds and offset π–π-stacking interactions. Adjacent chains are associated through C—H...π interactions. In the α-phase, molecules are linked by C—H...O and N—H...O hydrogen bonds, forming layers parallel to the (10-2) plane. In addition, π–π-stacking interactions and C—H...π(ring) interactions consolidate the packing. The packing is compared to that of the α-phase. The title compound was refined as a two-component twin.

In the title compound, C27H32BrNO5, the central 1,4-dihydropyridine ring adopts a shallow sofa conformation (with the C atom bearing the bromophenol ring as the flap), whereas the pendant cyclohexene rings both have twisted-boat conformations. The molecule features an intramolecular O—H...O hydrogen bond, which closes an S(8) ring. In the crystal, molecules are linked by C—H...O interactions, forming C(12) chains along the c-axis direction. The ethyl acetate grouping is disordered over two sets of sites in a 0.719 (11):0.281 (11) ratio.

In the title compound, C22H23ClN2O2S, the chlorophenyl ring is inclined to the pyridine ring of the isoquinoline ring system by 79.78 (4)°. The cyclohexane ring adopts a flattened boat conformation. In the crystal, dimers form through complementary sets of inversion-related O—H...O and C—H...O hydrogen bonds. These are connected into zigzag chains along the c-axis direction by pairwise C—H...N interactions that also form inversion dimers.

The basic building blocks of the three-dimensional structure of the title compound, C22H19N3O, are helical chains running along the [101] direction and formed by O—H...N hydrogen bonds. C—H...O hydrogen bonds between chains generate sheets which are then joined together by C—H...N hydrogen bonds. The two- and three-dimensional structures also feature two sets of C—H...π(ring) interactions.

In the crystal of the title molecule, C16H17NO6S, there are three sets of intermolecular C—H...O hydrogen bonds, as well as two sets of intermolecular C—H...π(ring) interactions. In addition, the thiazolidene rings participate in offset π–π stacking interactions [centroid–centroid distance = 3.685 (1) Å]. These generate small channels running parallel to the a axis with approximate cross-sections of 3.7 × 8.1 Å.

In the title compound, C14H17N3S, the cyclohexane ring adopts a chair conformation. The dihedral angle between the triazole and phenyl ring is 77.2 (3)°. In the crystal structure, C—H...S hydrogen link molecules into C(7) chains along the b-axis direction. The crystal studied was refined as as an inversion twin.

In the crystal of the title compound, C16H15N5S·C2H6OS, both the 1,2,4-triazole derivative molecules and the disordered [refined occupancy ratio = 0.604 (1):0.396 (1)] dimethyl sulfoxide solvent molecules form centrosymmetric dimers, by way of pairwise N—H...S and C—H...O hydrogen bonds, respectively. In the crystal, the two types of dimer are connected by N—H...O hydrogen bonds, forming infinite chains parallel to [101]. The packing is assisted by π–π stacking and C—H...π(ring) and N—H...π(ring) interactions.

In the title compound, C13H12N6O, the pyrazolo[3,4-b]pyrazine ring system is planar (r.m.s. deviation for the nine fitted atoms = 0.024 Å) and makes a dihedral angle of 5.72 (6)° with the pendent phenyl ring. The molecular conformation is stabilized by intramolecular N—H...O and C—H...N hydrogen bonds, each generating an S(6) loop. In the crystal, pairs of molecules are connected into inversion dimers by strong N—H...O hydrogen bonds, forming R22(8) ring motifs. These are linked into sheets parallel to (100) via N—H...N hydrogen bonds; π–π interactions between symmetry-related pyrazole and phenyl rings [centroid–centroid distances = 3.4453 (9) Å] within the sheets are also noted.

The title compound, C15H13NO2, crystallizes with two molecules (A and B) in the asymmetric unit. The carbazole ring systems of both molecules are close to planar (r.m.s deviations = 0.035 and 0.053 Å). In the crystal, A+A and B+B inversion dimers linked by pairs of O—H...O hydrogen bonds generate R22(8) loops and weak C—H...π interactions link the dimers into a three-dimensional network.

In the title compound, C22H18N2O3S, the two independent molecules in the asymmetric unit form a dimer via N—H...O hydrogen bonds. In the crystal, the molecular layers can be found in the (110) plane, connected by C—H...π interactions. Atoms of the furan ring of one independent molecule are disordered over two sets of sites with an occupancy ratio 0.735 (3):0.265 (3).

In the title compound, C22H18N4S·C2H6OS, the central triazolethione ring is inclined to the carbazole ring system by 13.97 (18)° and to the phenyl ring by 66.4 (1)°. The lattice solvent, dimethyl sulfoxide, is strongly hydrogen bonded to the triazolethione ring. In the crystal, the main molecules form columns parallel to the a axis, with the solvent molecules located between the columns. C—H...S hydrogen bonds and C—H...π(ring) interactions link adjacent columns. The crystal studied was refined as a two-component twin, with a fractional contribution to the minor domain of 0.0742 (14).

In the title compound, C23H17N3O, there is a short intramolecular C—H...O contact present, and the conformation about the C=N bond is E. The phenyl and benzylidene rings make dihedral angles of 28.21 (15) and 37.65 (14)° with the mean plane of the quinoline moiety. In the crystal, molecules are linked by N—H...O and C—H...O hydrogen bonds, forming chains propagating along [001], with the O atom accepting three hydrogen bonds.

The conformation of the title molecule, C19H19N3O4S·C2H6OS, which crystallized as a DMSO solvate, is partially determined by an intramolecular N—H...O hydrogen bond, forming an S(6) loop. The thienopyridine bicyclic system is almost planar, with an r.m.s. deviation of 0.002 Å. The benzene ring makes a dihedral angle of 65.44 (8)° with the mean plane of the thienopyridine bicyclic system. In the crystal, molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers with an R22(8) ring motif. Within the dimers, which stack along the a-axis direction, there is a weak π–π interaction [centroid-to-centroid distance = 3.5428 (11) Å] involving inversion-related thiophene rings. In addition, N—H...O and C—H...O hydrogen bonds help to consolidate the packing, via the solvent molecules.

In the title molecular salt, C8H20N+·C44H53O6S4−, the conformation of the anionic tetrathiacalix[4]arene, which is cone-shaped, is primarily determined by intramolecular O—H...O hydrogen bonds. There are also short intramolecular C— H...O contacts present. The guest species do not sit within the bowl of the calixarene. One of the t-butyl groups in the anion is disordered over two sets of sites with refined occupancies of 0.706 (6) and 0.294 (6). Atoms of both cations are equally disordered over centers of symmetry. In the crystal, extensive O—H...O and C—H...O hydrogen bonds and weak O—H...S interactions link the thiacalixarene anions and tetraethylammonium cations, forming a three-dimensional network.

In the title compound, C10H6ClNO2S, the dihedral angle between the planes of the 4-chlorophenyl and thiazolidine rings is 8.62 (9)°. In the crystal, molecules form undulating ribbons running approximately parallel to (101) through N—H...O hydrogen bonds.

The title compound, C20H24N6O2S2·2C2H6OS, has crystallographically imposed centrosymmetry. The packing is assisted by N—H...O, C—H...O and N—H...S interactions with the lattice solvent molecules, forming a two-dimensional network parallel to (1-10). The lattice dimethyl sulfoxide molecules (except for the S atoms) were modelled over two sites with refined occupancies of 0.831 (3):0.169 (3).

In the title compound, C15H17N3O2, the dihedral angle between the planes of the pyrazolidine and phenyl rings is 29.91 (6)°. The piperidine ring adopts a chair conformation. In the crystal, molecules are linked into chains running parallel to the a-axis direction by a combination of N—H...O and C—H...O hydrogen bonds. Furthermore, there exist C—H...π interactions and π–π stacking interactions [centroid-to-centroid distance = 3.5274 (10) Å] between the pyrazolidine rings of adjacent molecules.

The title compound, C15H12N4O2, contains two independent molecules in the asymmetric unit. These differ in terms of dihedral angles that the phenyl and 2-pyridyl rings subtend with the central five-membered ring; 15.2 (2) and 2.9 (2)°, respectively, in one molecule, 8.9 (2) and 5.1 (2)°for the second. In the crystal, the independent molecules each self-associate to form layers through N—H...O and C—H...O hydrogen bonding. The layers associate through π–π interactions between the phenyl rings and isolated carbon–carbon double bonds [shortest midpoint–centroid distance = 3.347 (4) Å]. The crystal studied was refined as a two-component twin.

In the title salt, C6H16N22+·2CNS−, the cyclohexane ring adopts a chair conformation. In the crystal, N—H...N hydrogen bonds enclose R42(8) rings involving two N atoms from the cyclohexane-1,4-diammonium cations as donors with the N atoms of two thiocyanate anions as acceptors. The crystal structure is further stabilized by intermolecular N—H...S hydrogen bonds that combine with these contacts to form a three-dimensional network.

The title compound, C24H20ClN5O2S·0.5H2O, has three independent molecules in the asymmetric unit and two water molecules of crystallization, one of which is equally disordered over two sites. The three unique organic molecules differ in the conformations of the substituents on the pyrazole ring. In the crystal, extensive O—H...O, O—H...N, N—H...O and C—H...O hydrogen bonding generates a three-dimensional network and C—H...π interactions are also observed.

In the crystal of the title salt, C5H12N+·C16H12ClN2O2S−, the cation adopts a chair conformation, and N—H...N and N—H...S hydrogen bonds form chains of alternating cations and anions running parallel to the c axis. The crystal structure contains a solvent-accessible void of 50 Å3, but no solvent molecule is located there.

In the title compound, C16H13ClN2O2S, the dihedral angle between the 4-chlorophenyl ring and the pyridine ring is 63.53 (6)°. There is an intramolecular C—H...O contact present. In the crystal, molecules are linked by pairs of N—H...S hydrogen bonds, forming inversion dimers. The dimers are linked by C—H...O and C—H...N hydrogen bonds, forming slabs parallel to the ab plane.

The structure of the title compound, C21H20N2O3, was originally determined at ambient temperature [Wu et al. (2007). Inorg. Chim. Acta, 360, 3069–3074]. In this determination, with data collected at 150 K, the asymmetric unit comprises two independent molecules (1 and 2) that differ considerably in their conformations. In particular, the methyl group at the mid-point of molecule 2 is disordered over two sites. This was modelled with restraints so that the geometries of the two components are comparable and the disorder components refined to an occupancy ratio of 0.750 (6):0.250 (6). Intramolecular O—H...N and intermolecular N—H...O hydrogen bonds stabilize the structure with significant additional input from C—H...π interactions.

In the title compound, C16H12N4OS, the bicyclic triazolothiadiazole core is approximately planar, with an r.m.s. deviation of 0.018 Å. The phenyl rings are inclined to its mean plane by 7.66 (7) and 71.79 (7)°. In the crystal, molecules are linked via a C—H...π interaction and a π–π interaction [intercentroid distance = 3.2942 (9) Å] involving inversion-related triazole rings. These interactions result in the formation of chains propagating along [10-1].

In the title compound, C24H20N4O2S, the benzimidiazole moiety is essentially planar within 0.020 (1) Å (r.m.s. deviation = 0.012 Å). Its mean plane makes a dihedral angle of 85.80 (3)° with the plane of the central pyridine ring while the methoxyphenyl ring makes a dihedral angle of 57.28 (4)° with this plane. In the crystal, N—H...N hydrogen bonds form sheets parallel to (010).

The title molecule, C23H18ClN5O4S, is in an `extended' conformation. The central triazole ring makes dihedral angles of 58.14 (6), 86.29 (6) and 41.99 (6)°, respectively, with the adjacent phenyl, chlorophenyl and nitrophenyl rings. In the crystal, molecules are linked via a pair of N—H...N hydrogen bonds with an R22(16) ring motif, forming an inversion dimer. The dimers are connected by C—H...O hydrogen bonds into a tape structure along [011]. C—H...π interactions between the tapes are also observed.

The packing in the crystal of the title molecule, C28H25N3O3S, is aided by intermolecular N—H...O and C—H...O hydrogen bonds. In the crystal, the ethyl group of the ester is disordered over two sets of sites with refined occupancies of 0.760 (8) and 0.240 (8).

The title molecule, C23H19ClN4O2S, is in an `extended' conformation. In the crystal, pairwise N—H...N and C—H...O hydrogen bonds lead to the formation of `stair-step' chains. C—H...π interactions further contribute to the consolidation of the molecular packing. The 4-chlorophenyl group is disordered over two sets of sites in a 0.948 (2):0.052 (2) ratio. The dihedral angle between the two components of the disordered chloro-substituted benzene ring is 15.76 (9) °.

In the title molecule, C22H22N2O4S, the bicyclic core is slightly folded [1.9 (1)°], while pairwise intermolecular N—H...O hydrogen bonding forms dimers across centers of symmetry. The dihedral angle between the phenyl ring an the six-membered ring of the bicyclic core is 75.50 (4)°. The molecular conformation is stabilized by an intramolecular N—H...O hydrogen bond with graph-set motif S(6) and by a weak C—H...O contact, forming an S(7) motif. In the crystal, π–π interactions [centroid-to-centroid distance = 3.7484 (10) Å] between phenyl rings and two weak C—H...π interactions are also observed.

The title compound, C10H7NO3S, crystallizes with four independent molecules in the asymmetric unit with slightly different conformations; the dihedral angles between the six- and five-membered rings are 2.6 (1), 1.09 (9), 8.6 (1) and 6.2 (1)°. In the crystal, molecules are linked by O—H...O and N—H...O hydrogen bonds, forming sheets lying parallel to (101).

The asymmetric unit of the title compound, C18H17N3O2, comprises three independent molecules (1, 2 and 3). In molecule 1, the dihedral angles between the pyrazolone ring and the pendant phenyl and hydroxybenzene rings are 54.43 (6) and 28.72 (6)°, respectively. The corresponding data for molecule 2 are 86.84 (6) and 25.69 (5)°, respectively, and for molecule 3 are 47.41 (7) and 17.09 (7)°, respectively. The three molecules feature an intramolecular C—H...O interaction, which closes an S(6) ring in each case. In the crystal, molecules are linked by O—H...O hydrogen bonds, which generate [100] chains incorporating all three asymmetric molecules. Two weak C—H...O interactions connect three independent molecules to each other along the c-axis direction.

The conformation of the title compound, C14H19N3S, is partially determined by an intramolecular N—H...N hydrogen-bond interaction, although the N—H...N angle of 108° is quite small. The cyclohexylidene ring has a chair conformation and its mean plane is inclined to the benzene ring by 46.30 (8)°. In the crystal, molecules are linked by pairs of N—H...S hydrogen bonds, forming inversion dimers, with an R22(8) ring motif. The dimers are reinforced by pairs of C—H...S hydrogen bonds, and are linked by further weak C—H...S hydrogen bonds, forming chains propagating along [100].

In the title compound, C16H12N2O3, the 2H-chromene moiety is essentially planar, with an r.m.s. deviation of the nine constituent atoms from the mean plane of 0.0093 Å, and makes a dihedral angle of 76.84 (3)° with the pendant phenyl ring. An intramolecular N—H...O hydrogen bond helps to determine the conformation of the side chain. In the crystal, N—H...O and N—H...N hydrogen bonds link the molecules, forming [100] chains.

The title compound, C21H21NO5, crystallizes with two molecules in the asymmetric unit. In each molecule, the central 1,4-dihydropyridine ring adopts a shallow sofa conformations (with the C atom bearing the phenol ring as the flap), whereas the pendant cyclohexene rings both have twisted-boat conformations. Each molecule features an intramolecular O—H...O hydrogen bond, which closes an S(8) ring. In the crystal, the molecules are linked by O—H...O, C—H...O and C—H...π interactions, forming a three-dimensional network.

In the title compound, C10H6BrNO3S, the dihedral angle between the thiazolidine ring (r.m.s. deviation = 0.014 Å) and the benzene ring is 5.78 (14)°. The S atom of the heterocyclic ring is syn to the OH group attached to the benzene ring. In the crystal, inversion dimers linked by pairs of N—H...O hydrogen bonds generate R22(8) loops. The dimers are linked into [001] ribbons by pairwise O—H...O hydrogen bonds with R22(18) motifs. There are no short contacts involving the Br atom.

In the title compound, C21H16N2O2, the naphthalene fragment is twisted slightly, as indicated by the dihedral angle of 3.2 (2)° between the two six-membered rings. The pendant 4-methoxyphenyl ring makes a dihedral angle of 86.08 (6)° with the central six-membered ring of the 4H-benzo[g]chromene ring system. In the crystal, molecules are linked by pairs of N—H...N hydrogen bonds, forming inversion dimers which are linked into chains propagating in the b-axis direction by N—H...O hydrogen bonds.

In the title compound, C14H17N3S, the dihedral angle between the planes of the benzene ring and the thiosemicarbazone group (r.m.s. deviation = 0.031 Å) is 8.45 (4)°. A short intramolcular N—H...N contact is seen. In the crystal, weak N—H...S hydrogen bonds connect the molecules into C(4) chains propagating in the [010] direction, with adjacent molecules in the chain related by 21 screw-axis symmetry.

The asymmetric unit of the title compound, C22H21N3O2, consists of two independent molecules (A and B) having differing conformations. The differences mainly concern the dihedral angles which the hydroxyphenyl and dimethylphenyl rings subtend to the central phenylene ring, these being 30.16 (6) and 58.60 (6)° in molecule A and 13.42 (7) and 60.31 (7)° in B. With the exception of the dimethyphenyl substituent, the conformations of the rest of each molecule are largely determined by intramolecular O—H...N and N—H...O hydrogen bonds. In the crystal, N—H...O hydrogen bonds link the molecules into chains extending parallel to the a axis in which the types of molecules alternate in an …A…B…A…B… fashion.

In the title compound, C23H24BrNO5, the central 1,4-dihydropyridine ring of the 1,2,3,4,5,6,7,8,9,10-decahydroacridine ring system adopts a half-chair conformation. The two cyclohexene rings fused to the central ring both have a twisted-boat conformation. The mean planes of the bromohydroxyphenyl ring and the major and minor components of the disordered ethyl aminoacetate moiety make dihedral angles of 78.99 (12), 85.9 (2) and 88.3 (9)°, respectively, with the 1,4-dihydropyridine ring. The terminal ethyl group of the ethyl aminoacetate moiety is disordered over two sets of sites with refined occupancies of 0.768 (17) and 0.232 (17). The molecular conformation is stabilized by an intramolecular O—H...O hydrogen bond, forming an S(8) ring motif. In the crystal, C—H...O hydrogen bonds connect the molecules into layers parallel to (001), enclosing R12(7) ring motifs.

In the title compound, C22H18ClN3O, the carbazole ring system is essentially planar (r.m.s deviation = 0.003 Å), and makes a dihedral angle of 9.01 (8)° with the plane of the chlorophenyl ring. In the crystal, neighbouring molecules are linked into centrosymmetric R22(8) dimers by pairs of N—H...O interactions and into a three-dimensional network by C—H...π interactions. The dimers are arranged into layers parallel to (010).