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The present study elaborates on the synthesis, crystal structure, and computational studies of two new ionic liquids. In the crystal structure, [C5H12N][C21H14ClN2O2S] (4a), the anions form chains along the a-axis direction through C—H···π(ring) interactions. These are connected into layers that run approximately parallel to the ac plane by a variety of hydrogen bonds. In the compound structure, [C5H12N][C18H15N2O2S] (4b), the two ions are primarily associated by an N—H···N hydrogen bond. In the crystal structure, layers parallel to the bc plane are formed by pairs of C—H···O and N—H···S hydrogen bonds and by C—H···π(ring) interactions. A theoretical study reveals that 4a has lower energy than 4b and is more stable. The NBO and DOS studies further confine the liquids’ structural reactivity and electronic properties. The quantum theory of atoms in a molecule (QTAIM) analysis reveals the important non-covalent interactions among the fragments and charge transfer. The global reactivity descriptors indicate their molecular reactivity relationship with the presence of functional groups. The remarkable polarizability (αo) and hyperpolarizability (βo) values indicate their optical and nonlinear optical (NLO) properties. Furthermore, the analysis performed by CrystalExplorer shows the intermolecular interactions and reactive sites between cations and anions in ionic liquids. The 2D fingerprint plots and Hirshfeld surfaces indicate the major interactions of crystals with neighboring elements in crystal packing. For both compounds, the H···H interactions are significantly higher than the other element interactions.

In the present work, we describe the synthesis of new tetrahydroisoquinoline derivatives and the crystal structures of two of them. Density functional theory (DFT) investigations at the B3LYP/6-31+G(d,p) level provided their structural reactivity and nonlinear optical properties. The low HOMO-LUMO gaps (EH-L) suggest a soft nature and higher reactivity, while calculated global reactivity descriptors provide assessments of their reactivity and electronic stability. The calculated natural bonding molecular orbital (NBO) charges show excellent charge separation (charge transfer) and identify the donor and acceptor parts of the molecules. Density of states (DOS) analyses show the newly generated energy states and reduced band gaps, which impart higher conductive properties. For surface reactivity, 3D MESP surfaces are plotted and show electron-rich sites near the nitrogen atoms of the tetrahydroisoquinoline rings. Nonlinear optical (NLO) properties of the crystals are predicted from calculated polarizability (αo) and hyperpolarizability (βo) values. For IVb, the αo and βo values are 415.53 and 1003.44 au. The remarkable value (1003.44 au) of the hyperpolarizability (βo) shows IVb has excellent NLO properties. Structural activity relationship analysis suggests that nitric oxide synthases are better targets for both compounds, and they were further subjected to molecular docking simulations to understand the binding efficiency. In addition, ADMET analyses were carried out to understand the potential activity of the molecules as drug candidates.

The multicomponent reaction of 4-nitrobenzaldehyde with acetophenone and urea in the presence of HCl was investigated, and, as a result, 4,5-bis(4-nitrophenyl)-8a-phenyl-decahydro-[1,3]diazino[4,5-d]pyrimidine-2,7-dione was synthesized. The structure of the synthesized compound was confirmed by the X-ray method. We performed Hirshfeld surfaces (HS) analysis and two-dimensional (2D) fingerprint plots for the studied compound to obtain surface reactivity and intermolecular interactions. The H∙∙∙H interactions were found to be higher, up to 32.2%, while the percentage C∙∙∙O contact was found to be the lowest among the reported interactions for single crystal packing. The energy framework analysis shows the strength of interaction energy within fragments of a single crystal at 3.08 A distances. The DFT study shows structural reactivity and a reduced HOMO-LUMO gap up to 4.0 eV. The NPA study reveals the reactivity and excellent charge transfer within the structure. The TD-DFT study reveals the absorbance in the UV region and excited state parameters during crucial transitions (transitions with maximum oscillator strength). The investigated compound shows excellent optical and nonlinear optical (NLO) properties, as indicated by its polarizability (αo) and hyperpolarizability (βo) values.

In the title molecule, C13H16N4O3, the mean planes of the phenyl and triazole rings are nearly perpendicular to one another as a result of the intramolecular C—H...O and C—H...π(ring) interactions. In the crystal, layers parallel to (101) are generated by O—H...N, N—H...O and N—H...N hydrogen bonds. The layers are connected by inversion-related pairs of C—H...O hydrogen bonds. The experimental molecular structure is close to the gas-phase geometry-optimized structure calculated by DFT methods. Hirshfeld surface analysis indicates that the most important interaction involving hydrogen in the title compound is the H...H contact. The contribution of the H...O, H...N, and H...H contacts are 13.6, 16.1, and 54.6%, respectively.

In the title molecule, C17H23NO2, the dihydroindole portion is planar (r.m.s. deviation = 0.0157 Å) and the nonyl substituent is in an `extended' conformation. In the crystal, the nonyl chains intercalate and the dihydroindoledione units are associated through C—H...O hydrogen bonds to form micellar blocks. Based on the Hirshfeld surface analysis, the most important intermolecular interaction is the H...H interaction.

In the title molecule, C21H25N3O, the 1-decyl substituents are in an extended conformation and intercalate in the crystal packing to form hydrophobic bands. The packing is further organized by π–π-stacking interactions between pyrrole and phenyl rings [centroid–centroid distance = 3.6178 (11) Å] and a C=O...π(pyrrole) interaction [3.447 (2) Å]. Hirshfeld surface analysis indicates that the H...N/N...H interactions make the highest contribution (17.4%) to the crystal packing.

The asymmetric unit of the title compound, C14H11N3O3, consists of two independent molecules having very similar conformations in which the indazole moieties are planar. The independent molecules are distinguished by small differences in the rotational orientations of the nitro groups. In the crystal, N—H...O and C—H...O hydrogen bonds form zigzag chains along the b-axis direction. Additional C—H...O hydrogen bonds link the chains into layers parallel to (10\overline{1}). These are connected by slipped π-stacking and C—H...π(ring) interactions.

The organic molecule in the title hydrate, C12H13NO3S·H2O, is folded across the S...N vector. Chains two molecules thick extending along the a-axis direction are formed by N—H...O and O—H...O hydrogen bonds. These interactions are reinforced by C—H...S hydrogen bonds and offset π-stacking interactions between centrosymmetrically related benzene rings. The chains are associated through C—H...O hydrogen bonds.

In the title compound, C22H32N2O3, the tetrahydroquinoxaline unit is planar. The ester substituent is nearly coplanar with this ring system as a result of an intramolecular N—H...O hydrogen bond. In the crystal, C—H...O hydrogen bonds and π-stacking interactions form oblique stacks which are connected into pairs by additional C—H...O hydrogen bonds. These pairs are further linked into thick sheets, with the n-decyl chains extending out from both surfaces as a result of a third set of C—H...O hydrogen bonds. Intercalation of the n-decyl chains completes the crystal packing.

The asymmetric unit of the title compound, C17H14N2O2, consists of two independent molecules differing mainly in the orientations of the phenyl and oxirane substituents. In the first molecule, the dihedral angle between the dihydroquinoxaline ring system and phenyl ring is 28.4 (2)° and the N—C—C—O torsion angle is 87.8 (5)°; corresponding data for the second molecule are 23.1 (2) and −85.6 (5)°, respectively. In the crystal, offset π-stacking interactions between the dihydroquinoxaline moieties form oblique stacks, which are connected into layers parallel to the bc plane by C—H...O hydrogen bonds and C—H...π(ring) interactions. Additional C—H...π(ring) interactions tie the layers together. The model was refined as a two-component twin.

In the title compound, C12H14N2O3, the conformation of the ester substituent is partially determined by an intramolecular N—H...O hydrogen bond. The crystal packing consists of layers parallel to (\overline{1}12) held together by N—H...O and C—H...O hydrogen bonds. The CH/NH portion of the heterocyclic ring is disordered over two sites in a 0.930 (5):0.070 (5) ratio with the disorder also extending to the O atom involved in the intramolecular N—H...O hydrogen bond.

In the title compound, C16H20N2O2, the seven-membered ring adopts a bowl-shaped conformation while the orientation of the 2-oxopropylidene substituent is determined by an intramolecular N—H...O hydrogen bond, which generates an S(6) ring. In the crystal, inversion dimers linked by pairs of very weak C—H...O interactions occur, which generate R22(8) loops.

In the title compound, C18H16N2O3, the dihydroquinoxaline moiety is planar (r.m.s. deviation = 0.0115 Å) and the majority of the ester substituent is nearly perpendicular to its mean plane. In the crystal, the molecules form oblique stacks along the b-axis direction through slipped π–π stacking interactions between adjacent dihydroquinoxaline units. C—H...O hydrogen bonds between the ester substituents on adjacent stacks form thick layers with the stacks on their outside surfaces. These layers extend along the c-axis direction and are coupled through C—H...π(ring) interactions. The structure was refined as a two-component twin.

The asymmetric unit of the title compound, C16H14N2O, contains three independent molecules differing primarily in the orientations of the benzyl groups. Each independent molecule forms inversion related dimers via offset π-stacking interactions. For two of these dimers, stacks are formed approximately along the a-axis direction by a combinations of C—H...N and C—H...π(ring) contacts, in addition to the offset π-stacking interactions. The third set of dimers are also stacked in the same direction but only by pairwise C—H...N hydrogen bonds.

In the title molecule, C19H18N2O2, the orientation of the oxopropylidene substituent is largely determined by an intramolecular N—H...O hydrogen bond. In the crystal, C—H...O hydrogen bonds form zigzag chains, which are elaborated into sheets lying parallel to (101) by complementary C—H...π interactions. Comparisons to the structure of the triclinic modification are made.

The asymmetric unit of the title compound, C10H8BrN3O2, contains two independent molecules differing primarily in the orientations of the allyl substituents [N—C—C=C torsion angles = −125.4 (16) and 116.0 (16)°]. The crystal packing involves slipped π–π stacking of indazole units, together with weak C—H...O and C—H...Br hydrogen bonds. The crystal studied was refined as a two-component twin.

In the title compound, C14H11N3O2, the indazole portion is planar to within 0.022 (2) Å and subtends a dihedral angle of 65.87 (7)° with the pendant benzene ring. In the crystal, oblique stacks of molecules extending along the a-axis direction are generated by π–π stacking interactions between the five- and six-membered rings [centroid–centroid separation = 3.6743 (19) Å] and the stacks are cross-linked by C—H...O hydrogen bonds.

The asymmetric unit of the title compound, C9H6ClN3O3, contains one full molecule in a general position and a half molcule sitting on a crystallographic mirror plane. In the crystal, molecules form stacks extending along the b-axis direction through a combination of offset π–π stacking between indazole units and C—Cl...π(ring) interactions with the six-membered rings of the same units. Elaboration of the C—Cl...π(ring) interactions along the a-axis direction forms slabs of molecules parallel to [001]. The stacks are joined by a combination of C—H...O and C—H...N hydrogen bonds.

In the title molecule, C9H7N3O3, the indazole moiety is essentially planar and the mean plane of the acetyl substituent is twisted by 5.3 (1)° from its plane. In the crystal, weak C—H...O and C—H...N hydrogen bonds form layers parallel to (102), which are associated through π-stacking interactions to form a three-dimensional network. The structure was refined as a two-component twin.

In the title compound, C9H8ClN3O2, the orientation of the ethyl substituent is partly determined by an intramolecular C—H...Cl hydrogen bond. The indazole moiety is slightly folded with an angle of 0.70 (8)° between the five- and six-membered rings. In the crystal, molecules pack in layers parallel to [100] through C—H...π(ring) and N...;O...π(ring) interactions.

In the title compound, C14H14N2O2, the dihydroquinoxaline moiety deviates slightly from planarity. In the crystal, zigzag chains are formed by inversion-related C—H...O hydrogen bonds. Adjacent chains are associated through pairwise C—H...π(ring) and π-stacking interactions.

In the title compound, C10H10ClN3O3, the side chain is oriented nearly perpendicular to the mean plane of the indazole ring system. In the crystal, complementary sets of O—H...N and C—H...O hydrogen bonds form chains of molecules stacked along the a-axis direction

In the title compound, C15H11NO, the anthracene unit is slightly bowed. Inversion-related pairs of O—H...N hydrogen bonds form dimers that are stacked along the b-axis direction by offset π–π stacking interactions between the anthracene units.

The asymmetric unit of the title compound, C9H6BrN3O3, consists of two independent molecules differing in the rotational orientations of the nitro and acetyl substituents. In the crystal, head-to-head π-stacking between pairs of adjacent molecules forms dimers which are associated into stacks by C—Br...π(ring) interactions. C—H...O hydrogen bonds tie the stacks together.

In the title compound, C17H17N3O, the indolone ring system is almost planar, with an angle of 0.76 (14)° between the five- and six-membered rings. The dicyanomethylidene substituent lies close to the indolene plane. In the crystal, offset π-stacking interactions between five- and six-membered rings of indolene stack the molecules along the c-axis direction.

In the title compound, C18H20N2O2, the diazepin-2-one ring adopts a tub conformation. The conformation of the acetyl group is partially determined by an intramolecular N—H...O hydrogen bond. In the crystal, pairwise C—H...O hydrogen bonds form inversion dimers.

In the title compound, C24H38N2O2, the heterocyclic ring (r.m.s. = 0.015 Å) deviates from planarity to a greater extent than the benzene ring (r.m.s. deviation = 0.007 Å). In the crystal, the molecules pack to form polar and non-polar regions. The major intermolecular interaction appears to be complementary π-stacking between oppositely oriented tetrahydroquinoxaline units.

The asymmetric unit of the title compound, C11H11N3O4, comprises two independent molecules, both of which display positional disorder of their ethyl chains in 0.868 (4):0.132 (4) and 0.839 (4):0.161 (4) ratios. The packing is directed by a combination of C—H...O hydrogen bonds and N—O...π interactions between nitro groups and the aromatic rings.

In the title compound, C16H12N2O3S, the indoline and thiophene rings are inclined to one another by 2.01 (2)°. The isoxazole ring adopts an envelope conformation, with the methine C atom as the flap, and its mean plane is inclined to the thiophene and indoline ring mean planes by 19.78 (14) and 20.83 (12)°, respectively. In the crystal, molecules are linked by C—H...O hydrogen bonds involving the same acceptor atom, forming chains propagating along [010]. The chains are linked by further C—H...O hydrogen bonds, forming slabs parallel to the (-303) plane. The slabs are linked by offset π–π interactions [intercentroid distance = 3.792 (1) Å], forming a three-dimensional supramolecular structure.

The asymmetric unit of the title complex, [ZnCl2(C12H12N4)], contains two independent molecules having similar conformations. The coordination about the ZnII atom is distorted tetrahedral, with the geometrical constraints of the chelating ligand responsible for the observed distortion. Each of the independent molecules forms chains in the crystal through pairs of N—H...Cl hydrogen bonds, using the pyrazole and benzimidazole N—H groups as donors. The first molecule forms chains running parallel to the b axis, while the other molecule affords the same kind of one-dimensional supramolecular structure parallel to the a axis. The structure was refined as a two-component twin with BASF = 0.0437 (4).

In the title compound, C16H11N3O, the molecular conformation is partially determined by an intramolecular C—H...π(ring) interaction. In the crystal, pairwise N—H...N hydrogen bonds form dimers, which associate into stacks through a combination of C—H...O, C—H...π(ring) and offset π–π stacking interactions.

In the title compound, C8H11N5O, the triazepine ring displays a boat conformation. Its mean plane is inclined to the triazole ring by 22.10 (9)°. In the crystal, molecules are linked by C—H...O hydrogen bonds to form chains parallel to the b-axis direction. Inversion-related chains are linked via offset π–π interactions between the triazole rings, forming ribbons propagating in the b-axis direction. The terminal CH3 group is disordered over two sets of sites, with a refined occupancy ratio of 0.48 (6):0.52 (6).

In the crystal of the title compound, C16H16N2O3, weak C—H...O hydrogen bonds involving the nitro group as acceptor form chains extending in the b-axis direction. The chains are arranged into layers by π–π stacking interactions along the c-axis direction between the substituted pyridine rings, separated by 3.624 (1) Å.

In the crystal of the title molecular salt, C16H34N5+·Cl−, (100) bilayers arise in which the tetradecylamino `tails' (which adopt extended conformations) interdigitate and the triazolium `heads' associate with the chloride anions through N—H...Cl hydrogen bonds.

In the title compound, C24H36N2O2, the orientation of the 2-oxopropylidene substituent is determined by the formation of an intramolecular N—H...O hydrogen bond. The benzodiazepine seven-membered ring adopts a slightly twisted boat conformation. The molecules pack in a bilayer fashion with the dodecyl chains intercalated to form the inner portion, and the benzodiazepine moieties on the outer surfaces.

In the title compound, C15H14N2O2, the seven-membered benzodiazepine ring adopts a twist-boat conformation and the two aromatic rings are inclined to one another by 81.06 (15)°. In the crystal, molecules are linked by N—H...O hydrogen bonds, forming chains propagating along the [10-1] direction. The chains are linked by C—H...O hydrogen bonds, forming sheets parallel to the ac plane. Within the sheets, there are N—H...π interactions present, and C—H...π interactions link the sheets to form a three-dimensional structure.

The title compound, C22H20N2O2, forms chains in the [001] direction in the monoclinic crystal, through N—H...O hydrogen bonding. The chains are associated via O—H...π(ring) and C—H...π(ring) interactions involving one phenyl ring and the benzene ring of the benzodiazepine as acceptors. For these intermolecular contacts, the H...π separations are close to 2.7 Å.

In the title omeprazole derivative, C20H21N3O3S, the benzimidazole ring is inclined to the pyridine ring by 21.21 (8)°. In the crystal, neighbouring molecules are linked by C—H...O hydrogen bonds, forming chains along the a-axis direction. Within the chains, there are offset π–π interactions [intercentroid distance = 3.880 (2) Å] involving neighbouring benzimidazole rings. There are no other significant intermolecular interactions present.

The title compound, C30H55N5O, forms a micellar structure in the crystal with the dodecyl chains intercalating and the bicyclic cores forming dimers across centres of symmetry, via weak C—H...N hydrogen bonds, and slipped π-stacking interactions between the five-membered rings.

In the molecule of the title compound, C6H7N5S, the triazole ring is planar, while the triazepine ring displays a boat conformation. The dihedral angle between the mean plane through the triazole and triazepine rings is 18.48 (8)°. In the crystal, molecules are linked into centrosymmetric dimers by N—H...N hydrogen bonds via eight-membered {...HNCN}2 synthons. Supramolecular layers in the ab plane are sustained by C—H...N and π–π interactions [inter-centroid separation between triazole rings = 3.2880 (16) Å]. Connections along the c axis occur between S atoms [S...S = 3.5972 (16) Å].

In the title molecule, C12H11N5O, the seven-membered ring derived from triazepine adopts a boat conformation. Intermolecular C—H...N hydrogen bonds and C—H...π-ring interactions form columns of molecules parallel to the a axis, which are further associated into the three-dimensional crystal structure by additional C—H...O hydrogen bonds.

In the title compound, C24H26N2O2, the dihedral angle between the benzene rings is 45.69 (7)°. In the crystal, the molecules form helical supramolecular chains running parallel to the b axis via weak C—H...O hydrogen bonds.

In the title molecule, C18H16N2O2, the seven-membered diazepinone ring adopts a boat conformation. An intramolecular N—H...O hydrogen bond encloses an S(6) ring. The two propynyl substituents each point away from the same face of the benzodiazepinone ring system. In the crystal, C—H...O hydrogen bonds form double chains of molecules along the c-axis direction.