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The title molecule, C25H23BrN2O2, adopts a cup shaped conformation with the distinctly ruffled imidazolidine ring as the base. In the crystal, weak C—H...O hydrogen bonds and C—H...π(ring) interactions form helical chains of molecules extending along the b-axis direction that are linked by additional weak C—H...π(ring) interactions across inversion centres. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (51.0%), C...H/H...C (21.3%), Br...H/H...Br (12.8%) and O...H/H...O (12.4%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 251.24 Å3 and 11.71%, respectively, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated by the dispersion energy.

In the title molecule, C20H18ClN3O2, the 2-chlorophenyl group is disordered to a small extent [occupancies 0.875 (2)/0.125 (2)]. The phenylacetamide moiety is nearly planar due to a weak, intramolecular C—H...O hydrogen bond. In the crystal, N—H...O hydrogen bonds and π-stacking interactions between pyridazine and phenyl rings form helical chains of molecules in the b-axis direction, which are linked by C—H...O hydrogen bonds and C—H...π(ring) interactions. A Hirshfeld surface analysis was performed, which showed that H...H, C...H/H...C and O...H/H...O interactions to dominate the intermolecular contacts in the crystal.

The dihydroimidazole ring in the title molecule, C20H20N2O3S, is slightly distorted and the lone pair on the tri-coordinate nitrogen atom is involved in intra-ring π bonding. The methylsulfanyl substituent lies nearly in the plane of the five-membered ring while the ester substituent is rotated well out of that plane. In the crystal, C—H...O hydrogen bonds form inversion dimers, which are connected along the a- and c-axis directions by additional C—H...O hydrogen bonds, forming layers parallel to the ac plane. The major contributors to the Hirshfeld surface are C...H/H...C, O...H/H...O and S...H/H...S contacts at 20.5%, 14.7% and 4.9%, respectively.

In the title molecule, C25H29N5O, the dihydroquinoxaline unit is not quite planar (r.m.s. deviation = 0.030 Å) as there is a dihedral angle of 2.69 (3)° between the mean planes of the constituent rings and the molecule adopts a hairpin conformation. In the crystal, the polar portions of the molecules are associated through C—H...O and C—H...N hydrogen bonds and C—H...π(ring) and C=O...π(ring) interactions, forming thick layers parallel to the bc plane and with the n-octyl groups on the outside surfaces.

In the title molecule, C11H11BrO3, the dihydroindene moiety is essentially planar but with a slight twist in the saturated portion of the five-membered ring. The methoxy groups lie close to the above plane. In the crystal, π-stacking interactions between six-membered rings form stacks of molecules extending along the a-axis direction, which are linked by weak C—H...O and C—H...Br hydrogen bonds. A Hirshfeld surface analysis was performed showing H...H, O...H/H...O and Br...H/H...Br contacts make the largest contributions to intermolecular interactions in the crystal.

The pyrazolopyrimidine moiety in the title molecule, C13H12N4S, is planar with the methylsulfanyl substituent lying essentially in the same plane. The benzyl group is rotated well out of this plane by 73.64 (6)°, giving the molecule an approximate L shape. In the crystal, C—H...π(ring) interactions and C—H...S hydrogen bonds form tubes extending along the a axis. Furthermore, there are π–π interactions between parallel phenyl rings with centroid-to-centroid distances of 3.8418 (12) Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H...H (47.0%), H...N/N...H (17.6%) and H...C/C...H (17.0%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 76.45 Å3 and 6.39%, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the cohesion of the crystal structure is dominated by the dispersion energy contributions.

Ethyl 2-[(2-oxo-2H-chromen-6-yl)oxy]acetate, C13H12O5, a member of the pharmacologically important class of coumarins, crystallizes in the monoclinic C2/c space group in the form of sheets, within which molecules are related by inversion centers and 21 axes. Multiple C—H...O weak hydrogen-bonding interactions reinforce this pattern. The planes of these sheets are oriented in the approximate direction of the ac face diagonal. Intersheet interactions are a combination of coumarin system π–π stacking and additional C—H...O weak hydrogen bonds between ethyl acetoxy groups.

In the title compound, C31H24N4O2, the dihydroquinoxaline units are both essentially planar with the dihedral angle between their mean planes being 64.82 (4)°. The attached phenyl rings differ significantly in their rotational orientations with respect to the dihydroquinoxaline planes. In the crystal, one set of C—H...O hydrogen bonds form chains along the b-axis direction, which are connected in pairs by a second set of C—H...O hydrogen bonds. Two sets of π-stacking interactions and C—H...π(ring) interactions join the double chains into the final three-dimensional structure.

In the title molecule, C21H17N3O2, the five-membered ring is slightly ruffled and dihedral angles between the pendant six-membered rings and the central, five-membered ring vary between 50.78 (4) and 86.78 (10)°. The exocyclic nitrogen lone pair is involved in conjugated π bonding to the five-membered ring. In the crystal, a layered structure is generated by O—H...N and N—H...O hydrogen bonds plus C—H...π(ring) and weak π-stacking interactions.

In the title molecule, C21H23N3O3, the imidazolidine ring slightly deviates from planarity and the morpholine ring exhibits the chair conformation. In the crystal, N—H...O and C—H...O hydrogen bonds form helical chains of molecules extending parallel to the c axis that are connected by C—H...π(ring) interactions. A Hirshfeld surface analysis reveals that the most important contributions for the crystal packing are from H...H (55.2%), H...C/C...H (22.6%) and H...O/O...H (20.5%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 236.78 Å3 and 12.71%, respectively. Evaluation of the electrostatic, dispersion and total energy frameworks indicates that the stabilization is dominated by the nearly equal electrostatic and dispersion energy contributions. The DFT-optimized molecular structure at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined molecular structure in the solid state. Moreover, the HOMO–LUMO behaviour was elucidated to determine the energy gap.

In the title compound, C17H12N2O, the quinoxaline moiety shows deviations of 0.0288 (7) to −0.0370 (7) Å from the mean plane (r.m.s. deviation of fitted atoms = 0.0223 Å). In the crystal, corrugated layers two molecules thick are formed by C—H...N hydrogen bonds and π-stacking interactions.

The quinoxaline moiety in the title molecule, C13H13ClN2O3, is almost planar (r.m.s. deviation of the fitted atoms = 0.033 Å). In the crystal, C—H...O hydrogen bonds plus slipped π-stacking and C—H...π(ring) interactions generate chains of molecules extending along the b-axis direction. The chains are connected by additional C—H...O hydrogen bonds. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...H (37.6%), H...O/O...H (22.7%) and H...Cl/Cl...H (13.1%) interactions.

The title molecule, [Fe2(C5H5)2(C23H17ClN2)]·C3H7NO, is twisted end to end and the central N/C/N unit is disordered. In the crystal, several C—H...π(ring) interactions lead to the formation of layers, which are connected by further C—H...π(ring) interactions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (60.2%) and H...C/C...H (27.0%) interactions. Hydrogen bonding, C—H...π(ring) interactions and van der Waals interactions dominate the crystal packing.

In the title compound, C31H24N4O2, the quinoxaline units are distinctly non-planar and twisted end-to-end. In the crystal, C—H...O and C—H...N hydrogen bonds link the molecules into chains extending along the a-axis direction. The chains are linked through π-stacking interactions between inversion-related quinoxaline moieties.

The indoline portion of the title molecule, C16H13NO2, is planar. In the crystal, a layer structure is generated by C—H...O hydrogen bonds and C—H...π(ring), π-stacking and C=O...π(ring) interactions. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (43.0%), H...C/C...H (25.0%) and H...O/O...H (22.8%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. The volume of the crystal voids and the percentage of free space were calculated to be 120.52 Å3 and 9.64%, respectively, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated by the dispersion energy contributions in the title compound. Moreover, the DFT-optimized structure at the B3LYP/6-311G(d,p) level is compared with the experimentally determined molecular structure in the solid state.

The title compound, C16H17N3O3, is racemic as it crystallizes in a centrosymmetric space group (P\overline{1}), although the trans disposition of substituents about the central C—C bond is established. The five- and six-membered rings are oriented at a dihedral angle of 75.88 (8)°. In the crystal, N—H...N hydrogen bonds form chains of molecules extending along the c-axis direction that are connected by inversion-related pairs of O—H...N into ribbons. The ribbons are linked by C—H...π(ring) interactions, forming layers parallel to the ab plane. A Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H...H (45.9%), H...N/N...H (23.3%), H...C/C...H (16.2%) and H...O/O...H (12.3%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. The volume of the crystal voids and the percentage of free space were calculated to be 100.94 Å3 and 13.20%, showing that there is no large cavity in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicates that the stabilization is dominated by the electrostatic energy contributions in the title compound. Moreover, the DFT-optimized structure at the B3LYP/6–311 G(d,p) level is compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

The title molecule, C29H44N8O, adopts a conformation resembling a two-bladed fan with the octyl chains largely in fully extended conformations. In the crystal, C—H...O hydrogen bonds form chains of molecules extending along the b-axis direction, which are linked by weak C—H...N hydrogen bonds and C—H...π interactions to generate a three-dimensional network. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (68.3%), H...N/N...H (15.7%) and H...C/C...H (10.4%) interactions.

In the title molecule, C7H7N3O, the pyrimidine ring is essentially planar, with the propynyl group rotated out of this plane by 15.31 (4)°. In the crystal, a tri-periodic network is formed by N—H...O, N—H...N and C—H...O hydrogen-bonding and slipped π–π stacking interactions, leading to narrow channels extending parallel to the c axis. Hirshfeld surface analysis of the crystal structure reveals that the most important contributions for the crystal packing are from H...H (36.2%), H...C/C...H (20.9%), H...O/O...H (17.8%) and H...N/N...H (12.2%) interactions, showing that hydrogen-bonding and van der Waals interactions are the dominant interactions in the crystal packing. Evaluation of the electrostatic, dispersion and total energy frameworks indicates that the stabilization is dominated by the electrostatic energy contributions. The molecular structure optimized by density functional theory (DFT) calculations at the B3LYP/6–311 G(d,p) level is compared with the experimentally determined structure in the solid state. The HOMO–LUMO behaviour was also elucidated to determine the energy gap.

In the title molecule, C8H7NO3S, the nitrogen atom has a planar environment, and the thiazine ring exhibits a screw-boat conformation. In the crystal, corrugated layers of molecules parallel to the ab plane are formed by N—H...O and C—H...O hydrogen bonds together with C—H...π(ring) and S=O...π(ring) interactions. The layers are connected by additional C—H...O hydrogen bonds and π-stacking interactions. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H...O/O...H (49.4%), H...H (23.0%) and H...C/C...H (14.1%) interactions. The volume of the crystal voids and the percentage of free space were calculated as 75.4 Å3 and 9.3%. Density functional theory (DFT) computations revealed N—H...O and C—H...O hydrogen-bonding energies of 43.3, 34.7 and 34.4 kJ mol−1, respectively. Evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via the electrostatic energy contribution. Moreover, the DFT-optimized structure at the B3LYP/ 6–311 G(d,p) level is compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

In the title compound, C20H28BrNO2, the indoline portion is almost planar and the 12-bromododecyl chain adopts an all-trans conformation apart from the gauche terminal C—C—C—Br fragment. A micellar-like structure is generated in the crystal by C—H...O hydrogen bonds and π-stacking interactions between indolinedione head groups and intercalation of the 12-bromododecyl tails. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (58.9%), H...O/O...H (17.9%) and H...Br/Br...H (9.5%) contacts. A density functional theory (DFT) optimized structure at the B3LYP/ 6–311 G(d,p) level shows good agreement with the experimentally determined molecular structure in the solid state.

The asymmetric unit of the title compound, C12H13N3O4, consists of two molecules differing to a small degree in their conformations. In the crystal, layers of molecules are connected by weak C—H...O hydrogen bonds and slipped π-stacking interactions. These layers lie parallel to (10\overline{1}) and are stacked along the normal to that plane. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing arise from H...H (43.5%) and H...O/O...H (30.8%) contacts. The density functional theory (DFT) optimized structure of the title compound at the B3LYP/ 6–311 G(d,p) level agrees well with the experimentally determined molecular structure in the solid state.

The asymmetric unit of the title molecule, C8H7NO3, consists of two molecules differing slightly in conformation and in their intermolecular interactions in the solid. The dihedral angle between the benzene and dioxolane rings is 0.20 (7)° in one molecule and 0.31 (7)° in the other. In the crystal, the two molecules are linked into dimers through pairwise O—H...N hydrogen bonds, with these units being formed into stacks by two different sets of aromatic π-stacking interactions. The stacks are connected by C—H...O hydrogen bonds. A Hirshfeld surface analysis indicates that the most significant contacts in the crystal packing are H...O/O...H (36.7%), H...H (32.2%) and C...H/H...C (12.7%).

The title compound, [Ni(C22H26S2)2], 1, is a square-planar D2h-symmetric compound that occurs on a general position in non-centrosymmetric tetragonal P41212 (No. 92) with ¼ eq of n-pentane (C5H12) as co-crystallite. Intraligand bond lengths show the dithiolene ligands to be in their half-oxidized radical monoanionic form. Intermolecular tBu-C—H...arenecentroid and tBu-C—H...NiS2C2 centroid close contacts guide the packing arrangement for 1.

In the title molecule, C7H6N4O3, the bicyclic ring system is planar with the carboxymethyl group inclined by 81.05 (5)° to this plane. In the crystal, corrugated layers parallel to (010) are generated by N—H...O, O—H...N and C—H...O hydrogen-bonding interactions. The layers are associated through C—H...π(ring) interactions. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...O/O...H (34.8%), H...N/N...H (19.3%) and H...H (18.1%) interactions. The volume of the crystal voids and the percentage of free space were calculated to be 176.30 Å3 and 10.94%, showing that there is no large cavity in the crystal packing. Computational methods revealed O—H...N, N—H...O and C—H...O hydrogen-bonding energies of 76.3, 55.2, 32.8 and 19.1 kJ mol−1, respectively. Evaluations of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via dispersion energy contributions. Moreover, the optimized molecular structure, using density functional theory (DFT) at the B3LYP/6–311G(d,p) level, was compared with the experimentally determined one. The HOMO–LUMO energy gap was determined and the molecular electrostatic potential (MEP) surface was calculated at the B3LYP/6–31G level to predict sites for electrophilic and nucleophilic attacks.

The cup-shaped conformation of the title molecule, C21H22N2O4, is largely determined by an intramolecular N—H...O hydrogen bond. In the crystal, double layers of molecules are formed by O—H...O and C—H...O hydrogen bonds. A Hirshfeld surface analysis was performed, which confirms the regions that are active for intermolecular interactions.

In the title compound, C24H23FN4O4S·0.25H2O, the dihydropyrimidine ring is distinctly non-planar, with the flap C atom deviating by 0.297 (2) Å from the least-squares plane. In the crystal, zigzag chains are formed by N—H...N hydrogen bonds parallel to [010] and are connected into layers parallel to (100) by O—H...O, O—H...F, C—H...O, C—H...F and C—H...N hydrogen bonds. Additional C—H...O hydrogen bonds connect the layers into a three-dimensional network. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from H...H (42.6%), O...H/H...O (16.8%) and C...H/H...C (15.5%) contacts.

The majority of the title molecule, C28H34ClN3O9S, is disordered over two closely spaced sets of sites; the site occupancy of the major component = 0.542 (3). The conformation of each component is approximately U-shaped with the chlorobenzene ring forming the base and the indolinyl and sulfamoyl groups the sides; an intramolecular C—H...Cl hydrogen bond possibly contributes to the stabilization of the conformation. In the crystal, a corrugated layer structure parallel to the ab plane is formed by C—H...O and C—H...Cl hydrogen bonds together with C—H...π(ring) interactions.

This study investigated the crystallographic and electronic properties of 1,5-benzodiazepine compounds, namely: cis-(3S,4S)-3-hydroxy-7,8-dimethyl-4-phenyl-1,3,4,5-tetrahydro-1,5-benzodiazepin-2-one 3b, trans-(3R,4R)-1-ethyl-3-hydroxy-7,8-dimethyl-4-phenyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepin-2-one 4, and trans-(3S,4S) 1-ethyl-3-ethoxy-7,8-dimethyl-4-phenyl-1,3,4,5-tetrahydro-1,5-benzodiazepin-2-one 5. Hirshfeld surface analysis was also applied to discern the intermolecular interactions, highlighting the significance of hydrogen bonding, van der Waals forces, and the influence of specific substituents. Furthermore, the MESP maps created using the density functional theory revealed the electrostatic nature of these molecules. The absence of dark blue regions on the MESP maps and variations due to different functional groups and substitutions were noteworthy findings. Collectively, this research offers crucial insights into the behaviour, interactions, and potential applications of new compounds. Finally, the anticancer effects of compounds 3b, 4, and 5 were evaluated against three cancer cell lines and one normal cell line, and the results showed that 3b and 4 had potent antiproliferative effects against all three cancer cell lines.

The asymmetric unit of the title compound, C8H7FN4O, consists of two independent molecules differing in the orientation of the azido group. Each molecule forms N—H...O hydrogen-bonded chains along along the c-axis direction with its symmetry-related counterparts and the chains are connected by C—F...π(ring), C=O...π(ring) and slipped π-stacking interactions. A Hirshfeld surface analysis of these interactions was performed.

The asymmetric unit of the title compound, C14H13NO4, contains three independent molecules, which differ slightly in conformation. Each contains an intramolecular N—H...O hydrogen bond. In the crystal, O—H...O hydrogen bonds form chains of molecules, which are linked into corrugated sheets parallel to (\overline{1}03) plane by C—H...O hydrogen bonds together with π interactions between the carbonyl groups and the 2-hydroxyphenyl rings. The layers are linked by further C—H...O hydrogen bonds. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (49.0%), H...O/O...H (28.3%) and H...C/C...H (10.9%) interactions. van der Waals interactions are the dominant interactions in the crystal packing. Moreover, density functional theory (DFT) optimized structures at the B3LYP/ 6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state. The HOMO–LUMO behavior was elucidated to determine the energy gap of 4.53 eV.

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.

In the title molecule, C23H20Cl2N4O3S, the thiazole ring is planar while the pyrimidine unit fused to it adopts a screw-boat conformation. In the crystal, thick sheets parallel to the bc plane are formed by N—H...N, C—H...N and C—H...O hydrogen bonds together with π–π interactions between the formamido carbonyl groups and the thiazole rings. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...H (30.9%), Cl...H/H...Cl (20.7%), C...H/H...C (16.8%) and O...H/H...O (11.4%) interactions.

In the title molecule, C9H10ClNO2, the methoxy group lies very close to the plane of the phenyl ring while the acetamido group is twisted out of this plane by 28.87 (5)°. In the crystal, a three-dimensional structure is generated by N—H...O, C—H...O and C—H...Cl hydrogen bonds plus C—H...π(ring) interactions. A Hirshfeld surface analysis of the intermolecular interactions was performed and indicated that C...H/H...C interactions make the largest contribution to the surface area (33.4%).

The triazole ring in the title molecule, C9H10N4O, is not quite coplanar with the six-membered ring to which it is fused, the dihedral angle between the two least-squares planes being 2.52 (6)°. In the crystal, a layered structure is formed by N—H...N and C—H...O hydrogen bonds plus slipped π-stacking interactions, with the fused cyclohexene rings projecting to either side.

The quinoxaline moiety in the title molecule, C18H17N3O2, is not quite planar and the p-tolyl group is rotationally disordered over two nearly equally populated sets of sites. In the crystal, N—H...O and C—H...O hydrogen bonds form chains extending along the b-axis direction. Due to the disorder of the p-tolyl rings, short C...C distances are observed between adjacent chains.

The quinoxaline unit in the title molecule, C18H16N4O5, is slightly puckered [dihedral angle between the rings = 2.07 (12)°] while the whole molecule adopts an L-shaped conformation. Intramolecular hydrogen bonding determines the orientation of the substituted phenyl ring and the amide nitrogen atom is almost planar. The packing in the crystal is governed by C—H...O hydrogen bonds and slipped π-stacking interactions.

In the title molecule, C17H16N2OS, the dihydroimidazolone ring is slightly puckered and the methylsulfanyl group is nearly coplanar with it. In the crystal, two sets of C—H...O hydrogen bonds form corrugated layers of molecules parallel to the ac plane. The layers pack with normal van der Waals contacts between them.

In the title compound, C12H10ClNO3, the dihydroquinoline moiety is not planar with a dihedral angle between the two ring planes of 1.61 (6)°. An intramolecular C—H...O hydrogen bond helps to establish the rotational orientation of the carboxyl group. In the crystal, sheets of molecules parallel to (10\overline{1}) are generated by C—H...O and C—H...Cl hydrogen bonds, and are stacked through slipped π-stacking interactions between inversion-related dihydroquinoline units. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (34.2%), H...O/O...H (19.9%), H...Cl/Cl...H (12.8%), H...C/C...H (10.3%) and C...C (9.7%) interactions. Computational chemistry indicates that in the crystal, the C—H...Cl hydrogen-bond energy is −37.4 kJ mol−1, while the C—H...O hydrogen-bond energies are −45.4 and −29.2 kJ mol−1. An evaluation of the electrostatic, dispersion and total energy frameworks revealed that the stabilization is dominated via the dispersion energy contribution. Density functional theory (DFT) optimized structures at the B3LYP/6–311 G(d,p) level are compared with the experimentally determined molecular structure in the solid state, and the HOMO—LUMO behaviour was elucidated to determine the energy gap.

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 title molecule, C25H28N2O5S, (alternative name ethyl 2-{[7-acetyl-4-cyano-6-hydroxy-8-(4-methoxyphenyl)-1,6-dimethyl-5,6,7,8-tetrahydroisoquinolin-3-yl]sulfanyl}acetate) the 4-methoxyphenyl group is disposed on one side of the bicyclic core and the oxygen atoms of the hydroxyl and acetyl groups are disposed on the other side. In the crystal, a layered structure parallel to the ac plane is generated by O—H...O and C—H...O hydrogen bonds plus C—H...π(ring) interactions.

The asymmetric unit of the title compound, C25H21N3O2S, comprises four molecules. Their conformations differ primarily in the orientations of the styryl and the N-phenylcarboxamido groups. In the crystal, intermolecular N—H...N, C—H...O and C—H...S hydrogen-bonding contacts as well a C—H...π(ring) interactions lead to the formation of a layer structure parallel to (010). Hirshfeld surface analysis revealed that H...H interactions represent the main contributions to the crystal packing.

The imidazolidine ring in the title molecule, C17H15BrN2O2, is slightly ruffled [r.m.s. deviation = 0.0192 Å], while the attached phenyl rings at the C atom at the position between the amine and carbonyl centres are rotated well out of its mean plane [dihedral angles with the imidazolidine ring = 63.60 (8) and 76.4 (1)°]. In the crystal, a three-dimensional network features N—H...O and C—H...O hydrogen bonds together with C—H...π(ring) interactions.

The substituted cyclopentadienyl ring in the title molecule, [Fe(C5H5)(C18H13ClN)], is nearly coplanar with the phenyl-1-(4-chlorophenyl)methanimine substituent, with dihedral angles between the planes of the phenylene ring and the Cp and 4-(chlorophenyl)methanimine units of 7.87 (19) and 9.23 (10)°, respectively. The unsubstituted cyclopentadienyl ring is rotationally disordered, the occupancy ratio for the two orientations refined to a 0.666 (7)/0.334 (7) ratio. In the crystal, the molecules pack in `bilayers' parallel to the ab plane with the ferrocenyl groups on the outer faces and the substituents directed towards the regions between them. The ferrocenyl groups are linked by C—H...π(ring) interactions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (46.1%), H...C/C... H (35.4%) and H...Cl/Cl...H (13.8%) interactions. Thus C—H...π(ring) and van der Waals interactions are the dominant interactions in the crystal packing.

A retro-Claisen reaction of 1-(4-oxo-4H-pyrido [1,2-a]pyrimidin-3-yl)butane-1,3-dione, 3, in the presence of potassium hydroxide and 4-dimethylamino-pyridine has been carried out, leading to 4-(dimethylamino)pyridin-1-ium 2-methyl-4-oxo-pyrido [1,2-a]pyrimidine-3-carboxylate 5. A plausible mechanism explaining the formation of the title compound has been proposed. A single-crystal X-ray diffraction analysis confirms the crystal structure of the isolated organic salt (5). In the crystal, the title compound adopts a layered structure where there are stacks of cations and anions formed by slipped π-stacking interactions. These stacks are linked by regions consisting of water molecules that are hydrogen-bonded together. DFT and Hirshfeld surface analysis supported the experimental results of the molecular geometry and the intercontacts between different units in the crystal. The druglikeness, ADMET properties, and predicted targets were investigated, and the observed results suggest that 5 may act as a carbonic anhydrase I inhibitor. The assumption is confirmed by docking 5 into the active binding site of carbonic anhydrase, which shows it to have good binding affinities and to form stable complexes with the active residues of carbonic anhydrase I.

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 title compound {systematic name: (S,E)-3-[4-(furan-2-yl)-2,3,4,5-tetrahydro-1H-benzo[b][1,4]diazepin-2-ylidene]-6-methyl-2H-pyran-2,4(3H)-dione}, C19H16N2O4, is constructed from a benzodiazepine ring system linked to furan and pendant dihydropyran rings, where the benzene and furan rings are oriented at a dihedral angle of 48.7 (2)°. The pyran ring is modestly non-planar [largest deviation of 0.029 (4) Å from the least-squares plane] while the tetrahydrodiazepine ring adopts a boat conformation. The rotational orientation of the pendant dihydropyran ring is partially determined by an intramolecular N—HDiazp...ODhydp (Diazp = diazepine and Dhydp = dihydropyran) hydrogen bond. In the crystal, layers of molecules parallel to the bc plane are formed by N—HDiazp...ODhydp hydrogen bonds and slipped π–π stacking interactions. The layers are connected by additional slipped π–π stacking interactions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H (46.8%), H...O/O...H (23.5%) and H...C/C...H (15.8%) interactions, indicating that van der Waals interactions are the dominant forces in the crystal packing. Computational chemistry indicates that in the crystal the N—H...O hydrogen-bond energy is 57.5 kJ mol−1.

The title molecule, C20H15NO3, adopts a Z-shaped conformation with the carboxyl group nearly coplanar with the dihydroquinoline unit. In the crystal, corrugated layers are formed by C—H...O hydrogen bonds and are stacked by C—H...π(ring) interactions. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...H (43.3%), H...C/C...H (26.6%) and H...O/O...H (16.3%) interactions. The optimized structure calculated using density functional theory at the B3LYP/ 6–311 G(d,p) level is compared with the experimentally determined structure in the solid state. The calculated HOMO–LUMO energy gap is 4.0319 eV.

In the title molecule, C21H20N2O3S, the styryl and ester substituents are displaced to opposite sides of the plane of the pyridine ring. In the crystal, C—H...O hydrogen bonds form chains extending parallel to the a-axis direction, which pack with partial intercalation of the styryl and ester substituents. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from H...H (43.6%), C...H/H...C (15.6%), O...H/H...O (14.9%) and N...H/H...N (11.2%) contacts.

The title molecule, C13H16N4O, adopts an angular conformation. In the crystal a layer structure is generated by N—H...O and N—H...N hydrogen bonds together with C—H...π(ring) interactions. Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H...H (53.8%), H...C/C...H (21.7%), H...N/N...H (13.6%), and H...O/O...H (10.8%) interactions. The optimized structure calculated using density functional theory (DFT) at the B3LYP/ 6–311 G(d,p) level is compared with the experimentally determined structure in the solid state. The calculated HOMO–LUMO energy gap is 5.0452 eV.

In the title molecule, C18H16N2O3, the dihydroquinoxaline moiety, with the exception of the N atom is essentially planar with the inner part of the methylpropanoate group (CH2—CH2—O) nearly perpendicular to it. In the crystal, inversion dimers formed by C—H...O hydrogen bonds are connected into oblique stacks by π-stacking and C—H...π(ring) interactions.