A new polymorph of the title compound, C10H13NO, was obtained by recrystallization of the commercial product from a water/ethanol mixture (1:1 v/v). Crystals of the previously reported racemic and homochiral forms of 2-phenyl­butyramide were grown from water–aceto­nitrile solution in 1:1 volume ratio [Khrustalev et al. (2014). Cryst. Growth Des. 14, 3360–3369]. While the previously reported racemic and enanti­opure forms of the title compound adopt very similar supra­molecular structures (hydrogen-bonded ribbons), the new racemic polymorph is stabilized by a single N—H⋯O hydrogen bond that links mol­ecules into chains along the c-axis direction with an anti­parallel (centrosymmetric) packing in the crystal. Hirshfeld mol­ecular surface analysis was employed to compare the inter­molecular inter­actions in the polymorphs of the title compound.

The title compound, C9H11NO2, was obtained as unexpected product from the reaction of (4-{2-benz­yloxy-5-[(E)-(3-chloro-4-methyl­phen­yl)diazen­yl]benzyl­idene}-2-phenyl­oxazol-5(4H)-one) with 2-meth­oxy­aniline in the presence of acetic acid as solvent. The amide group is not coplanar with the benzene ring, as shown by the C—N—C—O and C—N—C—C torsion angles of −2.5 (3) and 176.54 (19)°, respectively. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (53.9%), C⋯H/H⋯C (21.4%), O⋯H/H⋯O (21.4%) and N⋯H/H⋯N (1.7%) inter­actions.

The title compound, [Ni(C10H8N2)3](C9H5N4O)2·2H2O, crystallizes as a racemic mixture in the monoclinic space group C2/c. In the crystal, the 1,1,3,3-tetracyano-2-ethoxypropenide anions and the water molecules are linked by O—H⋯N hydrogen bonds, forming chains running along the [010] direction. The bpy ligands of the cation are linked to the chain via C—H⋯π(cation) inter­actions involving the CH3 group. The inter­molecular inter­actions were investigated by Hirshfeld surface analysis and two-dimensional fingerprint plots.

The solvated centrosymmmtric title compound, [Li2(C24H34O4P)2(C10H8N2)2]·2C7H8, was formed in the reaction between {Li[(2,6-iPr2C6H3-O)2POO](MeOH)3}(MeOH) and 2,2'-bi­pyridine (bipy) in toluene. The structure has monoclinic (P21/n) symmetry at 120 K and the asymmetric unit consists of half a complex mol­ecule and one mol­ecule of toluene solvent. The diaryl phosphate ligand demonstrates a μ-κO:κO'-bridging coordination mode and the 2,2'-bi­pyridine ligand is chelating to the Li+ cation, generating a distorted tetra­hedral LiN2O2 coordination polyhedron. The complex exhibits a unique dimeric Li2O4P2 core. One isopropyl group is disordered over two orientations in a 0.621 (4):0.379 (4) ratio. In the crystal, weak C—H⋯O and C—H⋯π inter­actions help to consolidate the packing. Catalytic systems based on the title complex and on the closely related complex {Li[(2,6-iPr2C6H3-O)2POO](MeOH)3}(MeOH) display activity in the ring-opening polymerization of ∊-caprolactone and l-dilactide.

The structure of zymonic acid (systematic name: 4-hy­droxy-2-methyl-5-oxo-2,5-di­hydro­furan-2-carb­oxy­lic acid), C6H6O5, which had previously eluded crystallographic determination, is presented here for the first time. It forms by intra­molecular condensation of parapyruvic acid, which is the product of aldol condensation of pyruvic acid. A redetermination of the crystal structure of pyruvic acid (systematic name: 2-oxo­propanoic acid), C3H4O3, at low temperature (90 K) and with increased precision, is also presented [for the previous structure, see: Harata et al. (1977). Acta Cryst. B33, 210–212]. In zymonic acid, the hy­droxy­lactone ring is close to planar (r.m.s. deviation = 0.0108 Å) and the dihedral angle between the ring and the plane formed by the bonds of the methyl and carb­oxy­lic acid carbon atoms to the ring is 88.68 (7)°. The torsion angle of the carb­oxy­lic acid group relative to the ring is 12.04 (16)°. The pyruvic acid mol­ecule is almost planar, having a dihedral angle between the carb­oxy­lic acid and methyl-ketone groups of 3.95 (6)°. Inter­molecular inter­actions in both crystal structures are dominated by hydrogen bonding. The common R22(8) hydrogen-bonding motif links carb­oxy­lic acid groups on adjacent mol­ecules in both structures. In zymonic acid, this results in dimers about a crystallographic twofold of space group C2/c, which forces the carb­oxy­lic acid group to be disordered exactly 50:50, which scrambles the carbonyl and hydroxyl groups and gives an apparent equalization of the C—O bond lengths [1.2568 (16) and 1.2602 (16) Å]. The other hydrogen bonds in zymonic acid (O—H⋯O and weak C—H⋯O), link mol­ecules across a 21-screw axis, and generate an R22(9) motif. These hydrogen-bonding inter­actions propagate to form extended pleated sheets in the ab plane. Stacking of these zigzag sheets along c involves only van der Waals contacts. In pyruvic acid, inversion-related mol­ecules are linked into R22(8) dimers, with van der Waals inter­actions between dimers as the only other inter­molecular contacts.

The title compound (systematic name: bis­{2-[4-(acet­yloxy)-1H-indol-3-yl]ethan-1-aminium} but-2-enedioate), 2C14H19N2O2+·C4H2O42−, has a single protonated psilacetin cation and one half of a fumarate dianion in the asymmetric unit. There are N—H⋯O hydrogen bonds between the ammonium H atoms and the fumarate O atoms, as well as N—H⋯O hydrogen bonds between the indole H atoms and the fumarate O atoms. The hydrogen bonds hold the ions together in infinite one-dimensional chains along [111].

The title pyridazinone derivative, C21H19ClN2O3, is not planar. The unsubstituted phenyl ring and the pyridazine ring are inclined to each other, making a dihedral angle of 17.41 (13)° whereas the Cl-substituted phenyl ring is nearly orthogonal to the pyridazine ring [88.19 (13)°]. In the crystal, C—H⋯O hydrogen bonds generate dimers with R22(10) and R22(24) ring motifs which are linked by C—H⋯O inter­actions, forming chains extending parallel to the c-axis direction. The inter­molecular inter­actions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the most significant contributions to the crystal packing are from H⋯H (44.5%), C⋯H/H⋯C (18.5%), H⋯O/H⋯O (15.6%), Cl⋯H/H⋯Cl (10.6%) and C⋯C (2.8%) contacts.

In the title quinoline derivative, C14H14ClNO3, there is an intra­molecular C—H⋯O hydrogen bond forming an S(6) graph-set motif. The mol­ecule is essentially planar with the mean plane of the ethyl acetate group making a dihedral angle of 5.02 (3)° with the ethyl 6-chloro-2-eth­oxy­quinoline mean plane. In the crystal, offset π–π inter­actions with a centroid-to-centroid distance of 3.4731 (14) Å link inversion-related mol­ecules into columns along the c-axis direction. Hirshfeld surface analysis indicates that H⋯H contacts make the largest contribution (50.8%) to the Hirshfeld surface.

A new quinoline-based hydrazone, C16H12ClN3, was synthesized by a condensation reaction of 2-chloro-3-formyl­quinoline with phenyl­hydrazine. The quinoline ring system is essentially planar (r.m.s. deviation = 0.012 Å), and forms a dihedral angle of 8.46 (10)° with the phenyl ring. The mol­ecule adopts an E configuration with respect to the central C=N bond. In the crystal, mol­ecules are linked by a C—H⋯π-phenyl inter­action, forming zigzag chains propagating along the [10overline{3}] direction. The N—H hydrogen atom does not participate in hydrogen bonding but is directed towards the phenyl ring of an adjacent mol­ecule, so linking the chains via weak N—H⋯π inter­actions to form of a three-dimensional structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (35.5%), C⋯H/H⋯C (33.7%), Cl⋯H/H⋯Cl (12.3%), N⋯H/H⋯N (9.5%) contacts.

In the title compound, the asymmetric unit comprises an N,N,N-trimethyl-1-(4-vinyl­phen­yl)methanaminium cation and a 4-vinyl­benzene­sulfonate anion, C12H18N+·C8H7O3S−. The salt has a polymerizable vinyl group attached to both the cation and the anion. The methanaminium and vinyl substituents on the benzene ring of the cation subtend angles of 86.6 (3) and 10.5 (9)° to the ring plane, while the anion is planar excluding the sulfonate O atoms. The vinyl substituent on the benzene ring of the cation is disordered over two sites with a refined occupancy ratio of 0.542 (11):0.458 (11). In the crystal, C—H⋯O hydrogen bonds dominate the packing and combine with a C—H⋯π(ring) contact to stack the cations and anions along the a-axis direction. Hirshfeld surface analysis of the salt and of the individual cation and anion components is also reported.

The mol­ecular structure of the title compound, C17H14ClFO3, consists of a 4-chloro-3-fluoro­phenyl ring and a 3,4-di­meth­oxy­phenyl ring linked via a prop-2-en-1-one spacer. The mol­ecule has an E configuration about the C=C bond and the carbonyl group is syn with respect to the C=C bond. The F and H atoms at the meta positions of the 4-chloro-3-fluoro­phenyl ring are disordered over two orientations, with an occupancy ratio of 0.785 (3):0.215 (3). In the crystal, mol­ecules are linked via pairs of C—H⋯O inter­actions with an R22(14) ring motif, forming inversion dimers. The dimers are linked into a tape structure running along [10overline{1}] by a C—H⋯π inter­action. The inter­molecular contacts in the crystal were further analysed using Hirshfield surface analysis, which indicates that the most significant contacts are H⋯H (25.0%), followed by C⋯H/H⋯C (20.6%), O⋯H/H⋯O (15.6%), Cl⋯H/H⋯Cl (10.7%), F⋯H/H⋯F (10.4%), F⋯C/C⋯F (7.2%) and C⋯C (3.0%).

The title compound, C21H16N2O2, consists of an imidazolidine unit linked to two phenyl rings and two prop-2-yn-1-yl moieties. The imidazolidine ring is oriented at dihedral angles of 79.10 (5) and 82.61 (5)° with respect to the phenyl rings, while the dihedral angle between the two phenyl rings is 62.06 (5)°. In the crystal, inter­molecular C—HProp⋯OImdzln (Prop = prop-2-yn-1-yl and Imdzln = imidazolidine) hydrogen bonds link the mol­ecules into infinite chains along the b-axis direction. Two weak C—HPhen⋯π inter­actions are also observed. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (43.3%), H⋯C/C⋯H (37.8%) and H⋯O/O⋯H (18.0%) inter­actions. Hydrogen bonding and van der Waals inter­actions are the dominant inter­actions in the crystal packing. Computational chemistry indicates that the C—HProp⋯OImdzln hydrogen-bond energy in the crystal is −40.7 kJ mol−1. Density functional theory (DFT) optimized structures at the B3LYP/6–311G(d,p) level are compared with the experimentally determined mol­ecular structure in the solid state. The HOMO–LUMO behaviour was elucidated to determine the energy gap.

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2'-bi­pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis­(4,4'-dimeth­oxy-2,2'-bi­pyri­dine)-1κ2N,N';2κ2N,N'-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ2O1,O2:2κ2O3,O4]dicopper(II) octa­hydrate, [Cu2(C12H12N2O2)2(C4H2O6)(H2O)]·8H2O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P21 with one chiral dinuclear complex and eight mol­ecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand's absolute configuration was confirmed via determination of the absolute structure. The complex mol­ecules exhibit an ansa-like structure with two planar, nearly parallel bi­pyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato `handle'. The complex and water mol­ecules give rise to a layered supra­molecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.

The coordination of the ligands with respect to the central atom in the complex bromido­tricarbon­yl[diphen­yl(pyridin-2-yl)phosphane-κ2N,P]rhenium(I) chloro­form disolvate, [ReBr(C17H14NP)(CO)3]·2CHCl3 or [κ2-P,N-{(C6H5)2(C5H5N)P}Re(CO)3Br]·2CHCl3, (I·2CHCl3), is best described as a distorted octa­hedron with three carbonyls in a facial conformation, a bromide atom, and a biting P,N-di­phenyl­pyridyl­phosphine ligand. Hirshfeld surface analysis shows that C—Cl⋯H inter­actions contribute 26%, the distance of these inter­actions are between 2.895 and 3.213 Å. The reaction between I and piperidine (C5H11N) at 313 K in di­chloro­methane leads to the partial decoord­ination of the pyridyl­phosphine ligand, whose pyridyl group is replaced by a piperidine mol­ecule, and the complex bromido­tricarbon­yl[diphen­yl(pyridin-2-yl)phosphane-κP](piperidine-κN)rhenium(I), [ReBr(C5H11N)(C17H14NP)(CO)3] or [P-{(C6H5)2(C5H5N)P}(C5H11N)Re(CO)3Br] (II). The mol­ecule has an intra­molecular N—H⋯N hydrogen bond between the non-coordinated pyridyl nitro­gen atom and the amine hydrogen atom from piperidine with D⋯A = 2.992 (9) Å. Thermogravimetry shows that I·2CHCl3 losses 28% of its mass in a narrow range between 318 and 333 K, which is completely consistent with two solvating chloro­form mol­ecules very weakly bonded to I. The remaining I is stable at least to 573 K. In contrast, II seems to lose solvent and piperidine (12% of mass) between 427 and 463 K, while the additional 33% loss from this last temperature to 573 K corresponds to the release of 2-pyridyl­phosphine. The contribution to the scattering from highly disordered solvent mol­ecules in II was removed with the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18] in PLATON. The stated crystal data for Mr, μ etc. do not take this solvent into account.

The title compounds, C14H10ClFN2OS (1) and C14H10BrFN2OS (2), were synthesized by two-step reactions. The dihedral angles between the aromatic rings are 31.99 (3) and 9.17 (5)° for 1 and 2, respectively. Compound 1 features an intra­molecular bifurcated N—H⋯(O,Cl) link due to the presence of the ortho-Cl atom on the benzene ring, whereas 2 features an intra­molecular N—H⋯O hydrogen bond. In the crystal of 1, inversion dimers linked by pairs of N—H⋯S hydrogen bonds generate R22(8) loops. The extended structure of 2 features the same motif but an additional weak C—H⋯S inter­action links the inversion dimers into [100] double columns. Hirshfeld surface analyses indicate that the most important contributors towards the crystal packing are H⋯H (26.6%), S⋯H/H.·S (13.8%) and Cl⋯H/H⋯Cl (9.5%) contacts for 1 and H⋯H (19.7%), C⋯H/H⋯C (14.8%) and Br⋯H/H⋯Br (12.4%) contacts for 2.

The title tetra­nuclear copper complex, [Cu4Cl6O(C6H9N3O3)4] or [Cu4Cl6O­(MET)4] [MET is 1-(2-hy­droxy­eth­yl)-2-methyl-5-nitro-1H-imidazole or metronidazole], contains a tetra­hedral arrangement of copper(II) ions. Each copper atom is also linked to the other three copper atoms in the tetra­hedron via bridging chloride ions. A fifth coordination position on each metal atom is occupied by a nitro­gen atom of the monodentate MET ligand. The result is a distorted CuCl3NO trigonal–bipyramidal coordination polyhedron with the axial positions occupied by oxygen and nitro­gen atoms. The extended structure displays O—H⋯O hydrogen bonding, as well as unusual short O⋯N inter­actions [2.775 (4) Å] between the nitro groups of adjacent clusters that are oriented perpendicular to each other. The scattering contribution of disordered water and methanol solvent mol­ecules was removed using the SQUEEZE procedure [Spek (2015). Acta Cryst. C71, 9–16] in PLATON [Spek (2009). Acta Cryst. D65, 148–155].

Reductive cyclization of 1,3,5-triphenyl- and 3-(2-meth­oxy­phen­yl)-1,5-di­phenyl­pentane-1,5-diones by zinc in acetic acid medium leads to the formation of 1,2,4-tri­phenyl­cyclo­pentane-1,2-diol [1,2,4-Ph3C5H5-1,2-(OH)2, C23H22O2, (I)] and 4-(2-meth­oxy­phen­yl)-1,2-di­phenyl­cyclo­pentane-1,2-diol [4-(2-MeOC6H4)-1,2-Ph2C5H5-1,2-(OH)2, C24H24O3, (II)]. Their single crystals have been obtained by crystallization from a THF/hexane solvent mixture. Diols (I) and (II) crystallize in ortho­rhom­bic (Pbca) and triclinic (Poverline{1}) space groups, respectively, at 150 K. Their asymmetric units comprise one [in the case of (I)] and three [in the case of (II)] crystallographically independent mol­ecules of the achiral (1R,2S,4r)-diol isomer. Each hydroxyl group is involved in one intra­molecular and one inter­molecular O—H⋯O hydrogen bond, forming one-dimensional chains. Compounds (I) and (II) have been used successfully as precatalyst activators for the ring-opening polymerization of ∊-caprolactone.

The reaction of 2,5-bis­(pyridin-4-yl)-1,3,4-oxa­diazole (4-pox) and thio­cyanate ions, used as co-ligand with nickel salt NiCl2·6H2O, produced the title complex, [Ni(NCS)2(C12H8N4O)2(H2O)2]. The NiII atom is located on an inversion centre and is octa­hedrally coordinated by four N atoms from two ligands and two pseudohalide ions, forming the equatorial plane. The axial positions are occupied by two O atoms of coordinated water mol­ecules. In the crystal, the mol­ecules are linked into a three-dimensional network through strong O—H⋯N hydrogen bonds. Hirshfeld surface analysis was used to investigate the inter­molecular inter­actions in the crystal packing.

The synthesis, spectroscopic data, crystal and mol­ecular structures of two N'-(1-phenyl­benzyl­idene)-2-(thio­phen-3-yl)acetohydrazides, namely N'-[1-(4-hy­droxy­phen­yl)benzyl­idene]-2-(thio­phen-3-yl)acetohydrazide, C13H10N2O2S, (3a), and N'-[1-(4-meth­oxy­phen­yl)benzyl­idene]-2-(thio­phen-3-yl)acetohydrazide, C14H14N2O2S, (3b), are described. Both compounds differ in the substituent at the para position of the phenyl ring: –OH for (3a) and –OCH3 for (3b). In (3a), the thio­phene ring is disordered over two orientations with occupancies of 0.762 (3) and 0.238 (3). The configuration about the C=N bond is E. The thio­phene and phenyl rings are inclined by 84.0 (3) and 87.0 (9)° for the major- and minor-occupancy disorder components in (3a), and by 85.89 (12)° in (3b). Although these dihedral angles are similar, the conformation of the linker between the two rings is different [the C—C—C—N torsion angle is −ac for (3a) and −sc for (3b), while the C6—C7—N9—N10 torsion angle is +ap for (3a) and −sp for (3b)]. A common feature in the crystal packing of (3a) and (3b) is the presence of N—H⋯O hydrogen bonds, resulting in the formation of chains of mol­ecules running along the b-axis direction in the case of (3a), or inversion dimers for (3b). The most prominent contributions to the surface contacts are those in which H atoms are involved, as confirmed by an analysis of the Hirshfeld surface.

In each of the two independent mol­ecules in the asymmetric unit of the title compound, [CdI2(C18H14N4O)], the N,O,N'-tridentate N'-[(E)-(phen­yl)(pyridin-2-yl-κN)methyl­idene]pyridine-2-carbohydrazide ligand and two iodide anions form an I2N2O penta­coordination sphere, with a distorted square-pyramidal geometry, with an I atom in the apical position. Both mol­ecules feature an intra­molecular N—H⋯N hydrogen bond. In the crystal, weak aromatic π–π stacking inter­actions [centroid–centroid separation = 3.830 (2) Å] link the mol­ecules into dimers.

This study is an investigation into the crystal structure of the biologically active drug mol­ecule riluzole [RZ, 6-(tri­fluoro­meth­oxy)-1,3-benzo­thia­zol-2-amine], C8H5F3N2OS, and its derivative, the riluzolium chloride salt [RZHCl, 2-amino-6-(tri­fluoro­meth­oxy)-1,3-benzo­thia­zol-3-ium chloride], C8H6F3N2OS+·Cl−. In spite of repeated efforts to crystallize the drug, its crystal structure has not been reported to date, hence the current study provides a method for obtaining crystals of both riluzole and its corresponding salt, riluzolium hydro­chloride. The salt was obtained by grinding HCl with the drug and crystallizing the obtained solid from di­chloro­methane. The crystals of riluzole were obtained in the presence of l-glutamic acid and d-glutamic acid in separate experiments. In the crystal structure of RZHCl, the –OCF3 moiety is perpendicular to the mol­ecular plane containing the riluzolium ion, as can be seen by the torsion angle of 107.4 (3)°. In the case of riluzole, the torsion angles of the four different mol­ecules in the asymmetric unit show that in three cases the tri­fluoro­meth­oxy group is perpendicular to the riluzole mol­ecular plane and only in one mol­ecule does the –OCF3 group lie in the same mol­ecular plane. The crystal structure of riluzole primarily consists of strong N—H⋯N hydrogen bonds along with weak C—H⋯F, C—H⋯S, F⋯F, C⋯C and C⋯S inter­actions, while that of its salt is stabilized by strong [N—H]+⋯Cl− and weak C—H⋯Cl−, N—H⋯S, C—H⋯F, C⋯C, S⋯N and S⋯Cl− inter­actions.

Five new crystal structures of perfluoro­pyridine substituted in the 4-position with phen­oxy, 4-bromo­phen­oxy, naphthalen-2-yl­oxy, 6-bromo­naphthalen-2-yl­oxy, and 4,4'-biphen­oxy are reported, viz. 2,3,5,6-tetra­fluoro-4-phen­oxy­pyridine, C11H5F4NO (I), 4-(4-bromo­phen­oxy)-2,3,5,6-tetra­fluoro­pyridine, C11H4BrF4NO (II), 2,3,5,6-tetra­fluoro-4-[(naphthalen-2-yl)­oxy]pyridine, C15H7F4NO (III), 4-[(6-bromo­naphthalen-2-yl)­oxy]-2,3,5,6-tetra­fluoropyridine, C15H6BrF4NO (IV), and 2,2'-bis­[(perfluoro­pyridin-4-yl)­oxy]-1,1'-biphenyl, C22H8F8N2O2 (V). The dihedral angles between the aromatic ring systems in I–IV are 78.74 (8), 56.35 (8), 74.30 (7), and 64.34 (19)°, respectively. The complete mol­ecule of V is generated by a crystallographic twofold axis: the dihedral angle between the pyridine ring and adjacent phenyl ring is 80.89 (5)° and the equivalent angle between the biphenyl rings is 27.30 (5)°. In each crystal, the packing is driven by C—H⋯F inter­actions, along with a variety of C—F⋯π, C—H⋯π, C—Br⋯N, C—H⋯N, and C—Br⋯π contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing.

The title compound, C11H8O5·(CH3)2SO, is a new coumarin derivative. The asymmetric unit contains two coumarin mol­ecules (A and B) and two di­methyl­sulfoxide solvent mol­ecules (A and B). The dihedral angle between the pyran and benzene rings in the chromene moiety is 3.56 (2)° for mol­ecule A and 1.83 (2)° for mol­ecule B. In mol­ecule A, the dimethyl sulfoxide sulfur atom is disordered over two positions with a refined occupancy ratio of 0.782 (5):0.218 (5). In the crystal, mol­ecules are linked by O—H⋯O hydrogen bonds, forming chains running along the c-axis direction. The chains are linked by C—H⋯O hydrogen bonds, forming layers parallel to the ac plane. In addition, there are also C—H⋯π and π–π inter­actions present within the layers. The inter­molecular contacts in the crystal have been analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots, which indicate that the most important contributions to the packing are from H⋯H (33.9%) and O⋯H/H⋯O (41.2%) contacts.

The asymmetric unit of the title 1:1 solvate, C14H14N4O2·C6H6 [systematic name of the oxalamide mol­ecule: N,N'-bis­(pyridin-4-ylmeth­yl)ethanedi­amide], comprises a half mol­ecule of each constituent as each is disposed about a centre of inversion. In the oxalamide mol­ecule, the central C2N2O2 atoms are planar (r.m.s. deviation = 0.0006 Å). An intra­molecular amide-N—H⋯O(amide) hydrogen bond is evident, which gives rise to an S(5) loop. Overall, the mol­ecule adopts an anti­periplanar disposition of the pyridyl rings, and an orthogonal relationship is evident between the central plane and each terminal pyridyl ring [dihedral angle = 86.89 (3)°]. In the crystal, supra­molecular layers parallel to (10overline{2}) are generated owing the formation of amide-N—H⋯N(pyrid­yl) hydrogen bonds. The layers stack encompassing benzene mol­ecules which provide the links between layers via methyl­ene-C—H⋯π(benzene) and benzene-C—H⋯π(pyrid­yl) inter­actions. The specified contacts are indicated in an analysis of the calculated Hirshfeld surfaces. The energy of stabilization provided by the conventional hydrogen bonding (approximately 40 kJ mol−1; electrostatic forces) is just over double that by the C—H⋯π contacts (dispersion forces).

In the title compound, C16H11Cl2N3O, the 4-meth­oxy-substituted benzene ring makes a dihedral angle of 41.86 (9)° with the benzene ring of the benzo­nitrile group. In the crystal, mol­ecules are linked into layers parallel to (020) by C—H⋯O contacts and face-to-face π–π stacking inter­actions [centroid–centroid distances = 3.9116 (14) and 3.9118 (14) Å] between symmetry-related aromatic rings along the a-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from Cl⋯H/H⋯Cl (22.8%), H⋯H (21.4%), N⋯H/H⋯N (16.1%), C⋯H/H⋯C (14.7%) and C⋯C (9.1%) inter­actions.

The asymmetric unit of the centrosymmetric title salt solvate, 2C17H17F6N2O+· C4H4O42−·CH3CH2OH, (systematic name: 2-{[2,8-bis­(tri­fluoro­meth­yl)quinolin-4-yl](hy­droxy)meth­yl}piperidin-1-ium butane­dioate ethanol monosolvate) comprises two independent cations, with almost superimposable conformations and each approximating the shape of the letter L, a butane­dioate dianion with an all-trans conformation and an ethanol solvent mol­ecule. In the crystal, supra­molecular chains along the a-axis direction are sustained by charge-assisted hy­droxy-O—H⋯O(carboxyl­ate) and ammonium-N—H⋯O(carboxyl­ate) hydrogen bonds. These are connected into a layer via C—F⋯π(pyrid­yl) contacts and π–π stacking inter­actions between quinolinyl-C6 and –NC5 rings of the independent cations of the asymmetric unit [inter-centroid separations = 3.6784 (17) and 3.6866 (17) Å]. Layers stack along the c-axis direction with no directional inter­actions between them. The analysis of the calculated Hirshfeld surface reveals the significance of the fluorine atoms in surface contacts. Thus, by far the greatest contribution to the surface contacts, i.e. 41.2%, are of the type F⋯H/H⋯F and many of these occur in the inter-layer region. However, these contacts occur at separations beyond the sum of the van der Waals radii for these atoms. It is noted that H⋯H contacts contribute 29.8% to the overall surface, with smaller contributions from O⋯H/H⋯O (14.0%) and F⋯F (5.7%) contacts.

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.

The syntheses and crystal structures of the title compounds, C14H8F4N2O2 and C14H8F4N2O3, are reported. In each crystal, the packing is driven by C—H⋯F inter­tactions, along with a variety of C—H⋯O, C—O⋯π, and C—F⋯π contacts. Hirshfeld surface analysis was conducted to aid in the visualization of these various influences on the packing: they showed that the largest contributions to the surface contacts arise from H⋯F/F⋯H inter­actions, followed by H⋯H and O⋯H/H⋯O.

The title coordination polymer, {[Cu3(C4H4N3O9)3(SeO4)(OH)]·2H2O}n or ([Cu3(μ3-OH)(trgly)3(SeO4)]·2H2O), crystallizes in the monoclinic space group P21/c. The three independent Cu2+ cations adopt distorted square-pyramidal geometries with {O2N2+O} polyhedra. The three copper centres are bridged by a μ3-OH anion, leading to a triangular [Cu3(μ3-OH)] core. 2-(1,2,4-Triazol-4-yl)acetic acid (trgly-H) acts in a deprotonated form as a μ3-κ3N1:N2:O ligand. The three triazolyl groups bridge three copper centres of the hydroxo-cluster in an N1:N2 mode, thus supporting the triangular geometry. The [Cu3(μ3-OH)(tr)3] clusters serve as secondary building units (SBUs). Each SBU can be regarded as a six-connected node, which is linked to six neighbouring triangles through carboxyl­ate groups, generating a two-dimensional uninodal (3,6) coordination network. The selenate anion is bound in a μ3-κ3O1:O2:O3 fashion to the trinuclear copper platform. The [Cu3(OH)(trgly)3(SeO4)] coordination layers and guest water mol­ecules are linked together by numerous O—H⋯O and C—H⋯O hydrogen bonds, leading to a three-dimensional structure.

In the title compound, C27H30N4O6·H2O, the two dioxolo rings are in envelope conformations, while the pyran ring is in a twisted-boat conformation. The pyradizine ring is oriented at dihedral angles of 9.23 (6) and 12.98 (9)° with respect to the pyridine rings, while the dihedral angle between the two pyridine rings is 13.45 (10)°. In the crystal, O—Hwater⋯Opyran, O—Hwater⋯Ometh­oxy­meth­yl and O—Hwater⋯Npyridazine hydrogen bonds link the mol­ecules into chains along [010]. In addition, weak C—Hdioxolo⋯Odioxolo hydrogen bonds and a weak C—Hmeth­oxy­meth­yl⋯π inter­action complete the three-dimensional structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (55.7%), H⋯C/C⋯H (14.6%), H⋯O/O⋯H (14.5%) and H⋯N/N⋯H (9.6%) inter­actions. Hydrogen-bonding and van der Waals inter­actions are the dominant inter­actions in the crystal packing. Electrochemical measurements are also reported.

The title salt, C16H15ClN3S+·Br−, is isotypic with (E)-3-[(4-fluoro­benzyl­idene)amino]-5-phenyl­thia­zolidin-2-iminium bromide [Khalilov et al. (2019). Acta Cryst. E75, 662–666]. In the cation of the title salt, the atoms of the phenyl ring attached to the central thia­zolidine ring and the atom joining the thia­zolidine ring to the benzene ring are disordered over two sets of sites with occupancies of 0.570 (3) and 0.430 (3). The major and minor components of the disordered thia­zolidine ring adopt slightly distorted envelope conformations, with the C atom bearing the phenyl ring as the flap atom. In the crystal, centrosymmetrically related cations and anions are linked into dimeric units via N—H⋯Br hydrogen bonds, which are further connected by weak C—H⋯Br contacts into chains parallel to the a axis. Furthermore, not existing in the earlier report of (E)-3-[(4-fluoro­benzyl­idene)amino]-5-phenyl­thia­zolidin-2-iminium bromide, C—H⋯π inter­actions and π–π stacking inter­actions [centroid-to-centroid distance = 3.897 (2) Å] between the major components of the disordered phenyl ring contribute to the stabilization of the mol­ecular packing. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions for the crystal packing are from H⋯H (30.5%), Br⋯H/H⋯Br (21.2%), C⋯H/H⋯C (19.2%), Cl⋯H/H⋯Cl (13.0%) and S⋯H/H⋯S (5.0%) inter­actions.

In the two isotypic title compounds, C14H8BrCl2N3O2, (I), and C14H8Cl3N3O2, (II), the substitution of one of the phenyl rings is different [Br for (I) and Cl for (II)]. Aromatic rings form dihedral angles of 60.9 (2) and 64.1 (2)°, respectively. Mol­ecules are linked through weak X⋯Cl contacts [X = Br for (I) and Cl for (II)], C—H⋯Cl and C—Cl⋯π inter­actions into sheets parallel to the ab plane. Additional van der Waals inter­actions consolidate the three-dimensional packing. Hirshfeld surface analysis of the crystal structures indicates that the most important contributions for the crystal packing for (I) are from C⋯H/H⋯C (16.1%), O⋯H/H⋯O (13.1%), Cl⋯H/H⋯Cl (12.7%), H⋯H (11.4%), Br⋯H/H⋯Br (8.9%), N⋯H/H⋯N (6.9%) and Cl⋯C/C⋯Cl (6.6%) inter­actions, and for (II), from Cl⋯H / H⋯Cl (21.9%), C⋯H/H⋯C (15.3%), O⋯H/H⋯O (13.4%), H⋯H (11.5%), Cl⋯C/C⋯Cl (8.3%), N⋯H/H⋯N (7.0%) and Cl⋯Cl (5.9%) inter­actions. The crystal of (I) studied was refined as an inversion twin, the ratio of components being 0.9917 (12):0.0083 (12).

Three new isotypic heteropolynuclear complexes, namely penta­aqua­carbonato­penta­kis­(glycinehydroxamato)nitrato­penta­copper(II)lanthanide(III) x-hydrate, [LnCu5(GlyHA)5(CO3)(NO3)(H2O)5]·xH2O (GlyHA2− is glycine­hydrox­amate, N-hy­droxy­glycinamidate or amino­aceto­hydroxamate, C2H4N2O22−), with lanthanide(III) (LnIII) = gadolinium (Gd, 1, x = 3.5), dysprosium (Dy, 2, x = 3.28) and holmium (Ho, 3, x = 3.445), within a 15-metallacrown-5 class were obtained on reaction of lanthanide(III) nitrate, copper(II) acetate and sodium glycinehydroxamate. Complexes 1–3 contain five copper(II) ions and five bridging GlyHA2− anions, forming a [CuGlyHA]5 metallamacrocyclic core. The LnIII ions are coordinated to the metallamacrocycle through five O-donor hydroxamates. The electroneutrality of complexes 1–3 is achieved by a bidentate carbonate anion coordinated to the LnIII ion and a monodentate nitrate anion coordinated apically to one of the copper(II) ions of the metallamacrocycle. The lattice parameters of complexes 1–3 are similar to those previously reported for an EuIII–CuII 15-metallacrown-5 complex with glycine­hydroxamate of proposed composition [EuCu5(GlyHA)5(OH)(NO3)2(H2O)4]·3.5H2O [Stemmler et al. (1999). Inorg. Chem. 38, 2807–2817]. High-quality X-ray data obtained for 1–3 have allowed a re-evaluation of the X-ray data solution proposed earlier for the EuCu5 complex and suggest that the formula is actually [EuCu5(GlyHA)5(CO3)(NO3)(H2O)5]·3.5H2O.

The title compound, C8H4Br2O4·C2H6O2, crystallizes with one-half of a 2,5-di­bromo­terephthalic acid (H2Br2tp) mol­ecule and one-half of an ethyl­ene glycol (EG) mol­ecule in the the asymmetric unit. The whole mol­ecules are generated by application of inversion symmetry. The H2Br2tp mol­ecule is not planar, with the di­bromo­benzene ring system inclined by a dihedral angle of 18.62 (3)° to the carb­oxy­lic group. In the crystal, the H2Br2tp and EG mol­ecules are linked into sheets propagating parallel to (overline{1}01) through O—H⋯O hydrogen bonds, thereby forming R44 (12) and R44 (28) graph-set motifs. Br⋯O and weak π–π stacking inter­actions are also observed. Hirshfeld surface analysis was used to confirm the existence of these inter­actions.

The di-substituted acetyl­ene residue in the title compound, C11H11NO3, is capped at either end by di-methyl­hydroxy and 4-nitro­benzene groups; the nitro substituent is close to co-planar with the ring to which it is attached [dihedral angle = 9.4 (3)°]. The most prominent feature of the mol­ecular packing is the formation, via hy­droxy-O—H⋯O(hy­droxy) hydrogen bonds, of hexa­meric clusters about a site of symmetry overline{3}. The aggregates are sustained by 12-membered {⋯OH}6 synthons and have the shape of a flattened chair. The clusters are connected into a three-dimensional architecture by benzene-C—H⋯O(nitro) inter­actions, involving both nitro-O atoms. The aforementioned inter­actions are readily identified in the calculated Hirshfeld surface. Computational chemistry indicates there is a significant energy, primarily electrostatic in nature, associated with the hy­droxy-O—H⋯O(hy­droxy) hydrogen bonds. Dispersion forces are more important in the other identified but, weaker inter­molecular contacts.

The reaction of 2-methyl­thio-5-amino-1,3,4-thia­diazole (Me-SNTD; C3H5N3S2) with copper(II) acetate monohydrate [Cu(OAc)2·H2O; C4H8CuO5] resulted in the formation of the title binuclear compound, [Cu2(C2H3O2)4(C3H5N3S2)2] or [Cu2(OAc)4(Me-SNTD)2]. The structure has triclinic (P overline{1}) symmetry with a crystallographic inversion centre located at the midpoint of the line connecting the Cu atoms in the dimer. These two Cu atoms of the dimer [Cu⋯Cu = 2.6727 (6) Å] are held together by four carboxyl­ate groups. Each Cu atom is further coordinated to the N atom of an Me-SNTD mol­ecule and exhibits a Jahn–Teller-distorted octa­hedral geometry. The dimers are connected into infinite chains by hydrogen bonds between the NH (Me-SNTD) and the carboxyl­ate groups of neighbouring mol­ecules, generating an R22(12) ring motif. The mol­ecules are further linked by C—H⋯π inter­actions between the thia­diazole rings and the methyl groups of the acetate units.

The isostructural title compounds, poly[piperazin-1-ium [di-μ-bromido-caesium]], {(C4H11N2)[CsBr2]}n, and poly[piperazin-1-ium [di-μ-bromido-rubidium]], {(C4H11N2)[RbBr2]}n, contain singly-protonated piperazin-1-ium cations and unusual ABr6 (A = Cs or Rb) trigonal prisms. The prisms are linked into a distinctive `curtain wall' arrangement propagating in the (010) plane by face and edge sharing. In each case, a network of N—H⋯N, N—H⋯Br and N—H⋯(Br,Br) hydrogen bonds consolidates the structure.

In the title di­thio­glycoluril derivative, C19H20N4O3S2, there is a difference in the torsion angles between the thio­imidazole moiety and the meth­oxy­phenyl groups on either side of the mol­ecule [C—N—Car—Car = 116.9 (2) and −86.1 (3)°, respectively]. The N—C—N bond angle on one side of the di­thio­glycoluril moiety is slightly smaller compared to that on the opposite side, [110.9 (2)° cf. 112.0 (2)°], probably as a result of the steric effect of the methyl group. In the crystal, N—H⋯S hydrogen bonds link adjacent mol­ecules to form chains propagating along the c-axis direction. The chains are linked by C—H⋯S hydrogen bonds, forming layers parallel to the bc plane. The layers are then linked by C—H⋯π inter­actions, leading to the formation of a three-dimensional supra­molecular network. Hirshfeld surface analysis and two-dimensional fingerprint plots were used to investigate the mol­ecular inter­actions in the crystal.

A new mononuclear NiII complex with bis­(pyridin-2-yl)amine (dpyam) and benzoate (benz), [Ni(C7H5O2)2(C10H9N3)], crystallizes in the monoclinic space group P21/c. The NiII ion adopts a cis-distorted octa­hedral geometry with an [NiN2O4] chromophore. In the crystal, the complex mol­ecules are linked together into a one-dimensional chain by symmetry-related π–π stacking inter­actions [centroid-to-centroid distance = 3.7257 (17) Å], along with N—H⋯O and C—H⋯O hydrogen bonds. The crystal packing is further stabilized by C—H⋯π inter­actions, which were investigated by Hirshfeld surface analysis.

Two compounds, 1,3-diethyl-5-{(2E,4E)-6-[(E)-1,3,3-tri­methyl­indolin-2-yl­idene]hexa-2,4-dien-1-yl­idene}pyrimidine-2,4,6(1H,3H,5H)-trione or TMI, C25H29N3O3, and 1,3-diethyl-2-sulfanyl­idene-5-[2-(1,3,3-tri­methyl­indolin-2-yl­idene)ethyl­idene]di­hydro­pyrimidine-4,6(1H,5H)-dione or DTB, C21H25N3O2S, have been crystallized and studied. These compounds contain the same indole derivative donor group and differ in their acceptor groups (in TMI it contains oxygen in the para position, and in DTB sulfur) and the length of the π-bridge. In both materials, mol­ecules are packed in a herringbone manner with differences in the twist and fold angles. In both structures, the mol­ecules are connected by weak C—H⋯O and/or C—H⋯S bonds.

The title compound, C18H16N4O, consists of a 3,6-bis­(pyridin-2-yl)pyridazine moiety linked to a 4-[(prop-2-en-1-yl­oxy)meth­yl] group. The pyridine-2-yl rings are oriented at a dihedral angle of 17.34 (4)° and are rotated slightly out of the plane of the pyridazine ring. In the crystal, C—HPyrd⋯NPyrdz (Pyrd = pyridine and Pyrdz = pyridazine) hydrogen bonds and C—HPrp­oxy⋯π (Prp­oxy = prop-2-en-1-yl­oxy) inter­actions link the mol­ecules, forming deeply corrugated layers approximately parallel to the bc plane and stacked along the a-axis direction. Hirshfeld surface analysis indicates that the most important contributions for the crystal packing are from H⋯H (48.5%), H⋯C/C⋯H (26.0%) and H⋯N/N⋯H (17.1%) contacts, hydrogen bonding and van der Waals inter­actions being the dominant inter­actions in the crystal packing. Computational chemistry indicates that in the crystal, the C—HPyrd⋯NPyrdz hydrogen-bond energy is 64.3 kJ mol−1. 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 behaviour was elucidated to determine the energy gap.

Lapachol acetate [systematic name: 3-(3-methyl­but-2-en­yl)-1,4-dioxonaph­thalen-2-yl acetate], C17H16O4, was prepared using a modified high-yield procedure and its crystal structure is reported for the first time 80 years after its first synthesis. The full spectroscopic characterization of the mol­ecule is reported. The mol­ecular conformation shows little difference with other lapachol derivatives and lapachol itself. The packing is directed by inter­molecular π–π and C—H⋯O inter­actions, as described by Hirshfeld surface analysis. The former inter­actions make the largest contributions to the total packing energy in a ratio of 2:1 with respect to the latter.

The structure of the title compound, C32H51NO6, was determined from 62-year-old crystals at room temperature and refined with 100 K data in a monoclinic (C2) space group. This compound with a triterpenoid structure, now confirmed by this study, played an important role in the determination of the structure of lanosterol. The mol­ecules pack in linear O—H⋯O hydrogen-bonded chains along the short axis (b), while parallel chains display weak van der Waals inter­actions that explain the needle-shaped crystal morphology. The structure exhibits disorder of the flexible methyl­heptane chain at one end of the main mol­ecule with a small void around it. Crystals of the compounds were resistant to data collection for decades with the available cameras and Mo Kα radiation single-crystal diffractometer in our laboratory until a new instrument with Cu Kα radiation operating at 100 K allowed the structure to be solved and refined.

The synthesis, crystal structure and structural motif of two thio­phene-based cyano­acrylate derivatives, namely, ethyl (E)-2-cyano-3-(3-methyl­thio­phen-2-yl)acrylate (1), C11H11NO2S, and ethyl (E)-2-cyano-3-(thio­phen-2-yl)acrylate (2), C10H9NO2S, are reported. Derivative 1 crystallized with two independent molecules in the asymmetric unit, and derivative 2 represents a new monoclinic (C2/m) polymorph. The mol­ecular conformations of 1 and the two polymorphs of 2 are very similar, as all non-H atoms are planar except for the methyl of the ethyl groups. The inter­molecular inter­actions and crystal packing of 1 and 2 are described and compared with that of the reported monoclinic (C2/m) polymorph of derivative 2 [Castro Agudelo et al. (2017). Acta Cryst. E73, 1287–1289].

The title compound, C11H9F3N4S, was synthesized from 2-(tri­fluoro­meth­yl)aniline by a multi-step reaction. It crystallizes in the non-centrosymmetric space group Pna21, with one mol­ecule in the asymmetric unit, and is constructed from a pair of aromatic rings [2-(tri­fluoro­meth­yl)phenyl and tetra­zole], which are twisted by 76.8 (1)° relative to each other because of significant steric hindrance of the tri­fluoro­methyl group at the ortho position of the benzene ring. In the crystal, very weak C—H⋯N and C—H⋯F hydrogen bonds and aromatic π–π stacking inter­actions link the mol­ecules into a three-dimensional network. To further analyse the inter­molecular inter­actions, a Hirshfeld surface analysis, as well as inter­action energy calculations, were performed.

Reaction of 2-(anthracen-9-yl)phenol (HOPhAn, 1) with divalent Yb[N(SiMe3)2]2·2THF in THF–toluene mixtures affords the mixed-valence YbII–YbIII dimer {[2-(anthracen-9-yl)phenolato-κO]bis­(tetra­hydro­furan)­ytterbium(III)}-tris­[μ-2-(anthracen-9-yl)phenolato]-κ4O:O;κO:1,2-η,κO-{[2-(anthracen-9-yl)phenolato-κO]ytterbium(II)} toluene tris­olvate, [Yb2(C20H13O)5(C4H8O)2]·3C7H7 or [YbIII(THF)2(OPhAn)](μ-OPhAn)3[YbII(OPhAn)]·3C7H7 (2), as the major product. It crystallized as a toluene tris­olvate. The Yb—O bond lengths in the crystal structure of this dimer clearly identify the YbII and YbIII centres. Inter­estingly, the formally four-coordinate YbII centre shows a close contact with one anthracene C—C bond of a bridging OPhAn ligand, bringing the formal coordination number to five.

In this paper, we describe the synthesis of a new di­hydro-2H-pyridazin-3-one derivative. The mol­ecule, C18H16N2O, is not planar; the benzene and pyridazine rings are twisted with respect to each other, making a dihedral angle of 11.47 (2)°, and the toluene ring is nearly perpendicular to the pyridazine ring, with a dihedral angle of 89.624 (1)°. The mol­ecular conformation is stabilized by weak intra­molecular C—H⋯N contacts. In the crystal, pairs of N—H⋯O hydrogen bonds link the mol­ecules into inversion dimers with an R22(8) ring motif. The inter­molecular inter­actions were investigated using Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots, revealing that the most important contributions for the crystal packing are from H⋯H (56.6%), H⋯C/C⋯H (22.6%), O⋯H/H⋯O (10.0%) and N⋯C/C⋯N (3.5%) inter­actions.

The title compound, C14H15BrClNO4, consists of a 5-bromo­indoline-2,3-dione unit linked to a 1-{2-[2-(2-chloro­eth­oxy)eth­oxy]eth­yl} moiety. In the crystal, a series of C—H⋯O hydrogen bonds link the molecules to form a supramolecular three-dimensional structure, enclosing R22(8), R22(12), R22(18) and R22(22) ring motifs. π–π contacts between the five-membered dione rings may further stabilize the structure, with a centroid–centroid distance of 3.899 (2) Å. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H⋯H (28.1%), H⋯O/O⋯H (23.5%), H⋯Br/Br⋯H (13.8%), H⋯Cl/Cl⋯H (13.0%) and H⋯C/C⋯H (10.2%) inter­actions. Hydrogen bonding and van der Waals inter­actions are the dominant inter­actions in the crystal packing. Density functional theory (DFT) optimized structures at the B3LYP/6-311G(d,p) level are compared with the experimentally determined mol­ecular structure in the solid state. The HOMO—LUMO behaviour was elucidated to determine the energy gap. The chloro­eth­oxy­ethoxyethyl side chain atoms are disordered over two sets of sites with an occupancy ratio of 0.665 (8):0.335 (6).

The title compounds, 4-(5-acetamido-3-acetyl-2-methyl-2,3-di­hydro-1,3,4-thia­diazol-2-yl)phenyl benzoate, C20H19N3O4S (I), 4-(5-acetamido-3-acetyl-2-methyl-2,3-di­hydro-1,3,4-thia­diazol-2-yl)phenyl isobutyrate 0.25-hydrate, C17H21N3O4S·0.25H2O (II), 4-(5-acetamido-3-acetyl-2-methyl-2,3-di­hydro-1,3,4-thia­diazol-2-yl)phenyl propionate, C16H19N3O4S (III) and 4-(5-acetamido-3-acetyl-2-methyl-2,3-di­hydro-1,3,4-thia­diazol-2-yl)phenyl cinnamate chloro­form hemisolvate, C22H21N3O4S·0.5CHCl3 (IV), all crystallize with two independent mol­ecules (A and B) in the asymmetric unit in the triclinic Poverline{1} space group. Compound II crystallizes as a quaterhydrate, while compound IV crystallizes as a chloro­form hemisolvate. In compounds I, II, III (mol­ecules A and B) and IV (mol­ecule A) the five-membered thia­diazole ring adopts an envelope conformation, with the tetra­substituted C atom as the flap. In mol­ecule B of IV this ring is flat (r.m.s. deviation 0.044 Å). The central benzene ring is in general almost normal to the mean plane of the thia­diazole ring in each mol­ecule, with dihedral angles ranging from 75.8 (1) to 85.5 (2)°. In the crystals of all four compounds, the A and B mol­ecules are linked via strong N—H⋯O hydrogen bonds and generate centrosymmetric four-membered R44(28) ring motifs. There are C—H⋯O hydrogen bonds present in the crystals of all four compounds, and in I and II there are also C—H⋯π inter­actions present. The inter­molecular contacts in the crystals of all four compounds were analysed using Hirshfeld surface analysis and two-dimensional fingerprint plots.

The title salt, C10H21N2O+·C7H12NO4S−, comprises a 3-methacryl­amido-N,N,N-tri­methyl­propan-1-aminium cation and a 2-acryl­amido-2-methyl­propane-1-sulfonate anion. The salt crystallizes with two unique cation–anion pairs in the asymmetric unit of the ortho­rhom­bic unit cell. The crystal studied was an inversion twin with a 0.52 (4):0.48 (4) domain ratio. In the crystal, the cations and anions stack along the b-axis direction and are linked by an extensive series of N—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network. Hirshfeld surface analysis was carried out on both the asymmetric unit and the two individual salts. The contribution of inter­atomic contacts to the surfaces of the individual cations and anions are also compared.