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A Schiff base 1-((3-nitrophenylimino)methyl)naphthalen-2-olate (HL) and its two novel complexes with Zn(II) and Co(II) metals were successfully synthesized and characterized by FTIR, 1H NMR, 13C NMR, elemental analysis, magnetic susceptibility, TGA and EIS-MS. Crystal of Schiff base was also characterized by X-ray analysis and experimental parameters were found in line with the theoretical parameters. Quantum mechanical approach was also used to compare structural and calculated parameters and to ensure the geometry of metal complexes. The photometric behaviors of all the synthesized compounds were investigated in a wide pH range using BR buffers. Appearance of isosbestic point suggested the existence of Schiff base molecules in different tautomeric forms. Binding of synthesized complexes with calf thymus DNA was explored by photometric and voltammetric titrations and binding constants were calculated. The results indicated that ligand and its metal complexes bind to DNA by intercalation mode. Docking studies indicate their binding possibilities with topoisomerase II. Moreover, all these prepared compounds were screened for enzyme inhibition, antibacterial, cytotoxic and in vivo antidiabetic activities and found active against one or other activity. This effort just provides preliminary data for some biological properties and which can act as foundation stone for their application in drug development. Keywords: Schiff base-metal complexes, Spectroscopy, X-ray analysis, DNA binding, Molecular docking

In the title compound, C10H9NS, the C—S—C bond angle is 99.41 (9)° and the dihedral angle between the trans-alkene fragment and the benzene ring is 16.49 (19)°. In the crystal, inversion dimers linked by pairs of extremely weak C—H...N interactions occur, as does a short S...N contact [3.2258 (19) Å].

The title Schiff base, C14H11NO3, crystallizes as a zwitterion (i.e. proton transfer from the carboxylic acid group to the imine N atom). The dihedral angle between the aromatic rings is 19.59 (6)° and an intramolecular N—H...O hydrogen bond closes an S(6) ring. In the crystal, inversion dimers linked by pairs of O—H...O hydrogen bonds generate R24(24) loops. The dimers are linked by C—H...O interactions, generating (211) sheets.

In the title compound, C13H14N4O2, which has approximate mirror symmetry, the dihedral angles between the triazole ring and the cyclopropane and pyridine rings are 87.1 (2) and 7.60 (9)°, respectively. In the crystal, inversion dimers linked by pairs of both C—H...N and C—H...O interactions generate R22(6) and R22(18) loops, respectively. Further C—H...N interactions form R22(10) loops and link the dimers into [110] chains.

In the title compound, C17H21N3O3, the non-planar (r.m.s. deviation = 0.212 Å) ethyl (oxo)acetate group is oriented towards the phenyl substituent. The triazole and benzene rings are twisted with respect to each other, making a dihedral angle of 41.69 (6)°. In the crystal, molecules are arranged into centrosymmetric R22(10) dimers via pairs of C—H...O interactions involving the ethyl (oxo)acetate groups. In addition, the triazole rings show π–π stacking interactions, with their centroids at a distance of 3.745 (2) Å.

In the title compound, C12H9BrN4O, the dihedral angle between the aromatic rings is 12.16 (12)°. An intramolecular N—H...N hydrogen bond closes an S(5) ring. In the crystal, C—H...O hydrogen bonds link the molecules into C(6) chains propagating in [010]. Very weak aromatic π–π stacking [centroid–centroid separations = 3.9189 (15) and 3.9357 (15) Å] is also observed.

In the title compound, [Fe(C5H5)(C25H17Cl3N3O)], the isolated cyclopentadienyl (Cp) ring is disordered over two set of sites in a 0.577 (8):0.423 (8) ratio. The dihedral angle between the other Cp ring and its attached benzene ring is 13.6 (3)°, and that between the benzene ring and the guanidine group is 64.8 (2)°. One of the N—H groups forms both an intra- and an intermolecular N—H...O hydrogen bond; the other N—H group does not form any hydrogen bonds. In the crystal, pairs of the intermolecular N—H...O hydrogen bonds link the molecules into inversion dimers.

The title compound, C13H12N4O2, crystallized with two independent molecules (A and B) in the asymmetric unit. Molecule B is planar to within 0.044 (3) Å for all non-H atoms, while molecule A is slightly twisted, with a dihedral angle of 6.29 (4)° between the mean planes of the pyrazine-2-carbohydrazide and 1-(2-hydroxyphenyl)ethanone moieties (r.m.s. deviations = 0.0348 and 0.0428 Å, respectively). S(5) and S(6) ring motifs are formed in both molecules due to the presence of intramolecular O—H...N and N—H...N hydrogen bonds. In the crystal, molecules A and B are linked by a C—H...O hydrogen bond. They stack along the a-axis direction, forming columns with π–π interactions involving inversion-related pyrazine and benzene rings [centroid–centroid distances = 3.5489 (13)–3.8513 (16) Å].

In the title compound, C12H9BrN4O, the N′-methylidenepyrazine-2-carbohydrazide and 4-bromobenzene groups are oriented at a dihedral angle of 10.57 (7)°. The hydrazide N—H group is involved in intramolecular N—H...N interaction, which generates an S(5) motif. A short C—H...O interaction is formed between the methylidene H atom and the carbonyl O atom. It connects molecules into chains extending along [100]. In addition, molecules are arranged into stacks extending along [010] via π–π interactions between pyrazine and benzene rings, with centroid–centroid distances of 3.837 (2) and 3.860 (2) Å.

In the title compound, [Sn(C6H5)3(C2H3OS2)], the SnIV atom adopts a distorted SnC3S tetrahedral coordination geometry. A short Sn...O contact [2.988 (4) Å] is also present. The phenyl rings are each disordered over two sets of sites with an occupancy ratio of 0.550 (8):0.450 (8). The crystal studied was found to be a racemic twin with a twin component ratio of 0.57 (18):0.43 (18).

In the title compound, C15H15NO2, the dihedral angle between the aromatic rings is 5.86 (6)°, and an intramolecular N—H...O hydrogen bond generates an S(6) motif, which helps to stabilize the enamine–keto tautomer. An intramolecular O—H...O hydrogen bond also occurs. In the crystal, inversion dimers linked by pairs of O—H...O hydrogen bonds generate R22(10) loops. A C—H...O interaction links the dimers into [010] chains and aromatic π–π stacking [centroid–centroid separation = 3.6131 (9) Å] also occurs.

The title compound, C32H48O4, which was extracted from the bark of Rhododendron arboreum, consists of five fused rings to which an acetate and seven methyl groups are attached. The A, D and E rings adopt chair conformations, the B ring is in a distorted chair and the C ring is in a half-chair conformation. The five-membered ring formed by the lactone group, which bridges from the A/B to the B/C ring junctions, is an approximate envelope with the C atom of the methyne group as the flap [displacement from the other four atoms = 0.753 (2) Å]. There are no identified directional interactions in the crystal structure.

In the title compound, C16H13Cl2N3O2S, the dihedral angle between the aromatic rings is 6.62 (2)° and the C=N—N=C torsion angle is 176.2 (4)°. The thiazine ring shows an envelope conformation, with the S atom displaced by 0.633 (6) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.037 Å). The Cl atom is an an axial conformation and is displaced by 2.015 (6) Å from the thiazine ring plane. In the crystal, molecules are linked by C—H...O interactions, generating a three-dimensional network. Very weak aromatic π–π stacking interactions [centroid–centroid separations = 3.928 (2) Å] are also observed.

In the title compound, C12H15NO5, the dihedral angle between the benzene ring and the C atoms of the terminal isopropyl group is 83.48 (16)°. Intramolecular N—H...O and O—H...O hydrogen bonds generate S(5) and S(6) rings, respectively. In the crystal, molecules are linked by O—H...O hydrogen bonds, generating C(7) chains propagating in [001]. Weak aromatic π–π stacking [centroid–centroid separation = 3.604 (3) Å] is also observed.

In the title compound, C17H16BrN3O2S, the dihedral angle between the aromatic rings is 1.24 (15)° and the C=N—N=C torsion angle is 167.7 (3)°. The conformation of the thiazine ring is an envelope, with the S atom displaced by 0.805 (3) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.027 Å). In the crystal, C—H...O interactions link the molecules into C(10) [010] chains. A weak C—H...π interaction is also observed.

In the title compound, C18H16ClN3O2S, the dihedral angle between the aromatic rings is 4.81 (2)° and the alkyl chain takes on an extended conformation [N—C—C—C = 179.2 (4)°]. The conformation of the thiazine ring is an envelope, with the S atom displaced by −0.805 (3) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.046 Å). The Cl atom is an axial conformation and is displaced by 1.761 (4) Å from the thiazine ring plane. In the crystal, inversion dimers linked by pairs of C—H...O interactions generate R22(20) loops and further C—H...O hydrogen bonds link the dimers into (001) sheets. Weak aromatic π–π stacking interactions [centroid–centroid separations = 3.870 (3) and 3.883 (3) Å] are also observed.

In the title compound, C15H12N2O7, the dihedral angle between the aromatic rings is 4.58 (13)° and the nitro group is rotated from its attached ring by 18.07 (17)°. Intramolecular N—H...O and O—H...O hydrogen bonds generate S(5) and S(6) rings, respectively. In the crystal, molecules are linked by O—H...O hydrogen bonds, generating [001] C(7) chains. The chains are linked by C—H...O interactions, forming a three-dimensional network, which incorporates R22(7) and R22(10) loops.

In the title compound, C19H21N3O2S, the dihedral angle between the aromatic rings is 6.7 (2)° and the C=N—N=C torsion angle is 178.0 (2)°. The conformation of the thiazine ring is an envelope, with the S atom displaced by 0.802 (2) Å from the mean plane of the other five atoms (r.m.s. deviation = 0.022 Å). In the crystal, molecules are linked by C—H...O interactions, generating C(5) chains propagating in [010]. A weak C—H...π interaction is also observed.

In the title compound, C16H13ClN4OS, the isatin ring system is oriented at dihedral angles of 10.60 (7) and 72.60 (3)° with respect to the thiosemicarbazide and 2-chlorobenzyl groups, respectively. The near planarity of the isatin and thiosemicarbazide groups [r.m.s. deviations of 0.0420 and 0.0163 Å, respectively] is reinforced by intramolecular N—H...O and N—H...N hydrogen bonds, which generate S(6) and S(5) rings, respectively. In the crystal, inversion dimers linked by pairs of N—H...O hydrogen bonds generate R22(8) loops. Aromatic π–π stacking interactions between the centroids of heterocyclic five-membered and benzene rings [distance = 3.6866 (11) Å] are also observed.

In the title compound, C15H14BrNO, the dihedral angle between the aromatic rings is 4.10 (11)° and the molecule is close to planar (r.m.s. deviation for the non-H atoms = 0.053 Å). An intramolecular O—H...N hydrogen bond closes an S(6) ring. In the crystal, very weak C—H...π interactions are observed.

The title compound, C19H18N4O4S, exists as a zwitterion in the solid state, with nominal proton transfer from a phenol group to the imine N atom. The 2,3-dihydroxybenzaldehyde fragment is oriented at a dihedral angle of 35.51 (11)° to the adajacent aniline group and makes a dihedral angle of 76.99 (6)° with the 4,6-dimethylpyrimidin-2-amine group. Intramolecular O—H...O and N—H...O hydrogen bonds close S(5) and S(6) rings, respectively; the same O atom accepts both bonds. In the crystal, polymeric chains along [001] are formed from molecules joined end-to-end by N—H...O and O—H...N hydrogen bonds; these feature R23(6) loops. The polymeric chains are linked by C—H...O interactions and there are π–π interactions between the pyrimidine rings with a centroid–centroid distance of 3.446 (2) Å.

In the title molecule, C9H6Cl2N2S, the mean planes of the benzene and thiazole rings make a dihedral angle of 54.18 (8)°. In the crystal, molecules are joined into dimers with an R22(8) ring motif by pairs of N—H...N hydrogen bonds. These dimers are linked by C—H...Cl interactions into layers parallel to (011). The thiazole rings form columns along the c-axis direction, with a centroid–centroid separation of 3.8581 (9) Å, indicating π–π interactions. An intramolecular C—H...S contact also occurs.

The title compound, C13H10N2O4, crystallized as the zwitterionic tautomer. As a result, the phenolate C—O− bond [1.296 (2) Å] is shorter than a normal Csp2—O(H) bond, and the azomethine C=N bond [1.314 (2) Å] is longer than a normal C=N double bond. The molecule is nearly planar, the mean plane of the nitro-substituted benzene ring forming dihedral angles of 9.83 (7) and 8.45 (9)° with the other benzene ring and with the nitro group, respectively. The molecular conformation is stabilized by an intramolecular N—H...O hydrogen bond. In the crystal, strong O—H...O hydrogen bonds link the molecules into double-stranded chains along the b-axis direction. Within the chains there are π–π interactions involving the benzene rings of adjacent molecules [centroid–centroid distance = 3.669 (1) Å]. The chains are linked via C—H...O hydrogen bonds, forming R21(6), R21(7) and R22(10) ring motifs.

In the title compound, C17H25NO2, the morpholine ring adopts a chair conformation. The benzene ring makes a dihedral angle of 39.81 (13)° with the basal plane of the morpholine group.

In the title compound, C18H21NO3, the naphthalene group and the basal plane of the morpholine ring (r.m.s. deviations = 0.0177 and 0.0069 Å, respectively) are oriented at a dihedral angle of 44.0 (2)°. In the crystal, molecules are linked by C—H...π interactions.

In the title compound, C12H9BrFNO, the dihedral angle between the aromatic rings is 51.39 (5)°; the C atom of the methoxy group is close to being coplanar with its attached ring (r.m.s. deviation = 0.0172 Å] and is oriented away from the pyridine ring. In the crystal, molecules interact by van der Waals forces.

In the title compound, C15H11NO3, the dihedral angle between the methoxybenzene and isoindole ring systems is 70.21 (3)°. The methoxy C atom is close to being coplanar with its attached ring [deviation = 0.133 (2) Å] and is oriented away from the isoindole moiety. In the crystal, inversion dimers linked by pairs of C—H...O hydrogen bonds generate R22(10) loops. Further C—H...O interactions lead to (010) infinite sheets and weak aromatic π–π stacking [centroid–centroid separations = 3.6990 (10) and 3.7217 (10) Å] is also observed.

In the title compound, C12H14N2S, the dihedral angle between the 1,3,5-trimethylbenzene and 1,3-thiazol-2-amine groups is 73.15 (4)°. In the crystal, inversion dimers linked by pairs of N—H...N hydrogen bonds generate R22(8) loops.

The asymmetric unit of the title compound, C14H12N2O4, contains two molecules that differ principally in the orientation of the acetamide substituent to the adjacent benzene ring with dihedral angles of 44.77 (7) and 19.06 (7)°. The dihedral angles between the benzene rings are 64.46 (4) and 80.84 (4)°. In the crystal, classical N—H...O hydrogen bonds form C(4) chains along [100]. These chains are interlinked by C—H...O contacts forming R22(10) rings. In the crystal, π–π interactions are observed with a distance of 3.5976 (18) Å between the centroids of the nitro-substituted benzene rings of one type of molecule.

In the title compound, C19H25NO2, the 3-ethoxy-2-hydroxybenzaldehyde group is almost planar (r.m.s. deviation = 0.029 Å). An intramolecular O—H...N hydrogen bond generates an S(6) ring. There are no intermolecular hydrogen bonds.

In the title compound, C20H17N3O4, the dihedral angles between the heterocyclic ring and the toluene and nitrobenzene rings are 4.21 (15) and 11.43 (14)°, respectively. The whole molecule is close to planar (r.m.s. deviation for the 27 non-H atoms = 0.171 Å). Two S(6) rings are formed due to intramolecular C—H...O and O—H...O hydrogen bonds. In the crystal, inversion dimers linked by pairs of C—H...O bonds generate R22(10) loops and further C—H...O bonds link the dimers along the b-axis direction. There exist π–π interactions between the heterocyclic rings at a centroid–centroid distance of 3.7126 (10) Å and between the centroids of the benzene rings at a distance of 3.8710 (16) Å.

In the title compound, C8H9BrN2O, the 1-bromo-4-methylbenzene group and the formic hydrazide moiety [r.m.s. deviations of 0.0129 and 0.0038 Å] are oriented at a dihedral angle of 80.66 (11)°. In the crystal, molecules are linked via strong N—H...O hydrogen bonds, leading to the formation of chains in the [010] direction. These chains are linked via weaker N—H...N and N—H...O hydrogen bonds, with R22(7) and R32(7) ring motifs, forming a two-dimensional network parallel to (001).

In the title compound, C11H7F2N, the fluorobenzene and the 2-fluoropyridine rings are oriented at a dihedral angle of 37.93 (5)°. In the crystal, only van der Waals interactions occur.

In the title compound, C17H18N2O3S, the dihedral angles between the thiophene ring and the ethyl ester group and the pyridine-4-carboxamide unit are 7.1 (2) and 9.47 (11)°, respectively. An intramolecular N—H...O hydrogen bond generates an S(6) ring. In the crystal, inversion dimers linked by pairs of C—H...O hydrogen bonds between the tetrahydro-1-benzothiophene and the pyridine-4-carboxamide residues generate R22(16) loops. There exists positional disorder in three methelene groups of the cyclohexane ring and the terminal C atom of the ethyl ester side chain in a 0.691 (14):0.309 (14) occupancy ratio.

In the title compound, C11H8FNO, the aromatic rings are oriented at a dihedral angle of 31.93 (6)°. In the crystal, molecules are linked by O—H...N hydrogen bonds, forming C(9) chains propagating along the c-axis direction. There are aromatic π–π stacking interactions between the pyridine rings [centroid–centroid separation = 3.7238 (16) Å].

In the title compound, C13H17NO3S, the dihedral angles between the thiophene ring and the ethyl ester and acetamide groups are 5.21 (13) and 10.06 (16)°, respectively. The cyclohezene ring adopts a half-chair conformation. An S(6) ring is formed due to an intramolecular N—H...O hydrogen bond. In the crystal, molecules are linked by C—H...O interactions between the tetrahydro-1-benzothiophene unit and the ethyl ester group, forming C(7) chains propagating along the b-axis direction.

In the title compound, C11H9NO3, the dihedral angle between the methoxybenzene and 1H-pyrrole-2,5-dione rings is 75.60 (10)°. The C atom of the methoxy group is close to coplanar with its attached ring [deviation = 0.208 (2) Å]. In the crystal, weak aromatic π–π stacking [centroid–centroid separation = 3.8563 (13) Å] occurs between inversion-related pairs of benzene rings.

The asymmetric unit of the title compound, C16H17NO2, contains two molecules in which the dihedral angles between the 3-ethoxy-2-hydroxybenzaldehyde and toluidine moieties are 16.87 (8) and 19.93 (6)°. S(6) rings are present in both molecules due to intramolecular O—H...N hydrogen bonds. In the crystal, one of the molecules is dimerized with an inversion-generated partner, due to two C—H...O interactions. This generates an R22(8) loop.

In the title compound, C18H18N2O5S2, the tolyl rings are oriented at a dihedral angle of 16.15 (11)° with respect to one another. The 5-methyl-1H-pyrazol-3-ol ring is roughly planar (r.m.s. deviation = 0.0231 Å) and subtends angles of 73.82 (8) and 89.85 (8)° with the tolyl rings. In the crystal, very weak π–π interactions between tolyl groups, with centroid–centroid distances of 4.1364 (19) and 4.0630 (16) Å, together with a C—H...π contact generate a three-dimensional network.

The asymmetric unit of the title compound, C16H16N4O2S, contains two molecules (A and B) with similar conformations: the benzene rings are oriented at dihedral angles of 80.94 (10)° and 84.54 (10)° with their adjacent 1H-benzimidazole groups. In the crystal, the molecules are connected by N—H...N hydrogen bonds, forming separate C(4) chains of both the A and B molecules along [010]. The A and B chains are cross-linked by several C—H...O interactions involving the benzene rings and the sulfonyl groups, which lead to R21(5) loops in the linkage of the chains.

In the title compound, C17H15N3O5S, the 2,3-dihydroxybenzaldehyde unit is oriented at a dihedral angles of 16.83 (10) and 78.87 (6)° with the anilinic and 5-methyl-1,2-oxazol-3-amine groups, respectively. An S(6) loop exists due to intramolecular O—H...N hydrogen bonding. In the crystal, inversion dimers with R22(8) rings are formed due to N—H...N hydrogen bonding between the 5-methyl-1,2-oxazol-3-amine groups. These dimers are interlinked by O—H...O hydrogen bonds, forming chains along [101] and resulting in R22(26) rings. π–π interactions occur between the central benzene rings with a centroid–centroid distance of 3.7928 (16) Å.

Two independent molecules are present in the asymmetric unit of the title compound, C12H10N2O, in which the 3-hydroxybenzaldehyde and the pyridin-3-amine units are almost planar [r.m.s. deviations of 0.0236 and 0.0116Å, respectively, in one molecule and 0.0245 and 0.0162Å, respectively, in the other] and are oriented at dihedral angles of 7.21 (7) and 14.77 (7)°. In the crystal, molecules of the same type form inversion dimers via pairs of O—H...N hydrogen bonds, forming R22(20) ring motifs. There exist π–π interactions between the benzene and pyridine rings of molecules of the same type with centroid–centroid distances of 3.7127 (10) and 3.8439 (10) Å.

In the title compound, C9H11N3O3, two molecules are present in the asymmetric unit in which the 4-hydroxy-3-methoxybenzaldehyde and hydrazinecarboxamide units are almost planar [with r.m.s. deviations 0.0212 and 0.0066 Å, respectively, in one molecule and 0.0346 and 0.0095 Å, respectively, in the other] and are oriented at dihedral angles of 9.7 (3) and 16.6 (3)°. In both molecules, two S(5) ring motifs are present due to N—H...N and O—H...O hydrogen bonds. In the crystal, the molecules are dimerized with each other due to pairs of N—H...O hydrogen bonds, forming an R22(8) ring motif. O—H...O hydrogen bonds lead to the formation of a three-dimensional network.

In the title compound, C11H7ClFN, the chlorobenzene and 2-fluoropyridine rings are oriented at a dihedral angle of 38.83 (5)°. In the crystal, there are no hydrogen-bonding interactions.

In the title compound, C11H6Cl2FN, the dichlorobenzene and the 2-fluoropyridine rings are oriented at a dihedral angle of 47.73 (3)°. In the crystal, pairs of C—H...N interactions link the molecules into dimers with R22(12) motifs. Molecules are arranged in stacks extending along [100] via π–π interactions with a centroid–centroid distance of 3.8889 (3) Å.

In the title compound, C24H18ClN3O2S, the dihedral angle between the benzene ring and the anthracene ring system is 41.10 (8)°. The thiazine ring has a half-chair conformation and the Cl atom is in an axial orientation. In the crystal, molecules are linked by C—H...O interactions, generating C(8) chains along [100]. A C—H...N short contact occurs in the molecule, generating an S(6) ring.

In the title compound, C15H16N2O2S, the dihedral angle between the 4-methoxyaniline and 2-aminobenzenethiole fragments is 35.60 (9)°. A short intramolecular N—H...S contact leads to an S(5) ring. In the crystal, molecules are consolidated in the form of polymeric chains along [010] as a result of N—H...O hydrogen bonds, which generate R32(18) and R43(22) loops. The polymeric chains are interlinked through C—H...O interaction and complete R22(8) ring motifs.

In the title compound, C17H13NO2S2, the dihedral angles between the 2-sulfanylidene-1,3-thiazolidin-4-one group and the pendant toluene and 2-hydroxybenzene rings are 74.62 (6) and 8.73 (12)°, respectively. An intramolecular C—H...S interaction occurs. In the crystal, inversion dimers linked by pairs of O—H...O hydrogen bonds generate R22(16) loops. This link is reinforced by a pair of C—H...O hydrogen bonds. The dimers are connected by weak C—H...S interactions.

The title compound, C6H4Br2ClN, is almost planar (r.m.s. deviation = 0.024 Å) and two intramolecular N—H...Br hydrogen bonds generate S(5) rings. In the crystal, N—H...Br hydrogen bonds link the molecules into chains propagating in [010].

In the title compound, C19H16N2O3S·C2H6O, the 4-hydroxybenzylidene group is oriented at dihedral angles of 73.17 (7) and 77.06 (7)° with respect to the aniline groups. The sulfonyl group make dihedral angles of 44.89 (13) and 59.16 (12)° with the adjacent aniline groups. In the crystal, a two-dimensional polymeric network parallel to (010) is formed by N—H...O, O—H...N and O—H...O hydrogen bonds. There also exist π–π interactions with a distance of 3.5976 (18) Å between the centroids of hydroxyphenyl rings.