The title compound, C15H15NO2, is a Schiff base that exists in the keto–enamine tautomeric form and adopts a Z configuration. The mol­ecule is almost planar, with the two phenyl rings twisted relative to each other by 9.60 (18)°. There is an intra­molecular N—H⋯O hydrogen bond present forming an S(6) ring motif. In the crystal, pairs of O—H⋯O hydrogen bonds link adjacent mol­ecules into inversion dimers with an R22(18) ring motif. The dimers are linked by very weak π–π inter­actions, forming layers parallel to (overline{2}01). Hirshfeld surface analysis, two-dimensional fingerprint plots and the mol­ecular electrostatic potential surfaces were used to analyse the inter­molecular inter­actions, indicating that the most important contributions for the crystal packing are from H⋯H (55.2%), C⋯H/H⋯C (22.3%) and O⋯H/H⋯O (13.6%) inter­actions.

The title compounds, C24H22O6 (I) and C24H22O6 (II), each crystallize with half a mol­ecule in the asymmetric unit. The whole mol­ecule of compound (I) is generated by twofold rotation symmetry, the twofold axis bis­ecting the central benzene ring. The whole mol­ecule of compound (II) is generated by inversion symmetry, the central benzene ring being located on an inversion center. In (I), the outer benzene rings are inclined to each other by 59.96 (10)° and by 36.74 (9)° to the central benzene ring. The corresponding dihedral angles in (II) are 0.0 and 89.87 (12)°. In the crystal of (I), mol­ecules are linked by C—H⋯O hydrogen bonds and C—H⋯π inter­actions, forming ribbons propagating along the [10overline{1}] direction. In the crystal of (II), mol­ecules are linked by C—H⋯O hydrogen bonds, forming a supra­molecular framework. The Hirshfeld surface analyses indicate that for both compounds the H⋯H contacts are the most significant, followed by O⋯H/H⋯O and C⋯H/H⋯C contacts.

The title compound, C14H12N2O4, is a Schiff base that exists in the keto–enamine tautomeric form and adopts a Z configuration. The mol­ecule is almost planar, the rings making a dihedral angle of 4.99 (7)°. The mol­ecular structure is stabilized by an intra­molecular N—H⋯O hydrogen bond forming an S(6) ring motif. In the crystal, inversion-related mol­ecules are linked by pairs of O—H⋯O hydrogen bonds, forming dimers with an R22(18) ring motif. The dimers are linked by pairs of C—H⋯O contacts with an R22(10) ring motif, forming ribbons extended along the [2overline{1}0] direction. Hirshfeld surface analysis, two-dimensional fingerprint plots and the mol­ecular electrostatic potential surfaces were used to analyse the inter­molecular inter­actions present in the crystal, indicating that the most important contributions for the crystal packing are from H⋯H (33.9%), O⋯H/H⋯O (29.8%) and C⋯H/H⋯C (17.3%) inter­actions.

The crystal structure of the title mol­ecular complex, [Ag2{VO2F2}2(C13H17N3O2)4]·4H2O, supported by the heterofunctional ligand tr-ad-COOH [1-(1,2,4-triazol-4-yl)-3-carb­oxy­adamantane] is reported. Four 1,2,4-triazole groups of the ligand link two AgI atoms, as well as AgI and VV centres, forming the heterobimetallic coordination cluster {AgI2(VVO2F2)2(tr)4}. VV exists as a vanadium oxofluoride anion and possesses a distorted trigonal–bipyramidal coordination environment [VO2F2N]. A carb­oxy­lic acid functional group of the ligand stays in a neutral form and is involved in hydrogen bonding with solvent water mol­ecules and VO2F2− ions of adjacent mol­ecules. The extended hydrogen-bonding network is responsible for the crystal packing in the structure.

In the title compound, C61H15ClN2O3, the heterocyclic ring adopts an envelope conformation, folded across the N⋯N line, with the 2,5-di­meth­oxy­phenyl unit occupying a quasi-axial site. There are two N—H⋯O hydrogen bonds in the structure: one hydrogen bond links mol­ecules related by a 41 screw axis to form a C(6) chain, and the other links inversion-related pairs of mol­ecules to form an R22(8) ring. The ring motif links all of the chains into a continuous three-dimensional framework structure. Comparisons are made with the structures of some related compounds.

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 binuclear CoIII complex, [Co2(C9H8BrNOS)2(C18H16Br2N2O2S2)]·C3H7NO, with a Schiff base ligand formed in situ from cyste­amine (2-amino­ethane­thiol) and 5-bromo­salicyl­aldehyde crystallizes in the space group P21. It was found that during the synthesis the ligand undergoes spontaneous oxidation, forming the new ligand H2L' having an S—S bond. Thus, the asymmetric unit consists of one Co2(L)2(L') mol­ecule and one DMF solvent mol­ecule. Each CoIII ion has a slightly distorted octa­hedral S2N2O2 coordination geometry. In the crystal, the components are linked into a three-dimensional network by several S⋯ Br, C⋯ Br, C—H⋯Br, short S⋯C (essentially shorter than the sum of the van der Waals radii for the atoms involved) contacts as well by weak C—H⋯O hydrogen bonds. The crystal studied was refined as an inversion twin.

The title benzo­furan derivatives 2-amino-5-hy­droxy-4-(4-nitro­phen­yl)benzo­furan-3-carboxyl­ate (BF1), C19H18N2O6, and 2-meth­oxy­ethyl 2-amino-5-hy­droxy-4-(4-nitro­phen­yl)benzo­furan-3-carboxyl­ate (BF2), C18H16N2O7, recently attracted attention because of their promising anti­tumoral activity. BF1 crystallizes in the space group Poverline{1}. BF2 in the space group P21/c. The nitro­phenyl group is inclined to benzo­furan moiety with a dihedral angle between their mean planes of 69.2 (2)° in BF1 and 60.20 (6)° in BF2. A common feature in the mol­ecular structures of BF1 and BF2 is the intra­molecular N—H⋯Ocarbon­yl hydrogen bond. In the crystal of BF1, the mol­ecules are linked head-to-tail into a one-dimensional hydrogen-bonding pattern along the a-axis direction. In BF2, pairs of head-to-tail hydrogen-bonded chains of mol­ecules along the b-axis direction are linked by O—H⋯Ometh­oxy hydrogen bonds. In BF1, the butyl group is disordered over two orientations with occupancies of 0.557 (13) and 0.443 (13).

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.

The mol­ecule of the title compound, C27H37NO3, was prepared by [3 + 2] 1,3-dipolar cyclo­addition of 4-n-octyl­phenyl­nitrile oxide and 4-tert-but­oxy­styrene, the latter compound being a very useful inter­mediate to the synthesis of liquid-crystalline materials. In the mol­ecule, the benzene rings of the n-octyloxyphenyl and tert-but­oxy­phenyl groups form dihedral angles of 2.83 (7) and 85.49 (3)°, respectively, with the mean plane of the isoxazoline ring. In the crystal, mol­ecules are linked by weak C—H⋯O hydrogen inter­actions into chains running parallel to the b axis.

Six reaction products of ZnII and NiII with pyridine-2,6-di­carb­oxy­lic acid (H2Lig1), 4-chloro­pyridine-2,6-di­carb­oxy­lic acid (H2Lig2) and 4-hy­droxy­pyridine-2,6-di­carb­oxy­lic acid (H2Lig3) are used to pinpoint the structural consequences of crystal field stabilization by an incomplete d shell. The pseudo-octa­hedral ZnII coordination sphere in bis­(6-carb­oxy­picolinato)zinc(II) trihydrate, [Zn(C7H4NO4)2]·3H2O or [Zn(HLig1)2]·3H2O, (1), is significantly less regular than that about NiII in the isostructural compound bis­(6-carb­oxy­picolinato)nickel(II) trihydrate, [Ni(C7H4NO4)2]·3H2O or [Ni(HLig1)2]·3H2O, (2). The ZnII complexes poly[(4-chloro­pyridine-2,6-di­carboxyl­ato)zinc(II)], [Zn(C7H2ClNO4)]n or [Zn(Lig2)]n, (3), and poly[[(4-hy­droxy­pyridine-2,6-di­carboxyl­ato)zinc(II)] monohydrate], {[Zn(C7H3NO5)]·H2O}n or {[Zn(Lig3)]·H2O}n, (4), represent two-dimensional coordination polymers with chelating and bridging pyridine-2,6-di­carboxyl­ate ligands in which the coordination polyhedra about the central cations cannot be associated with any regular shape; their coordination environments range between trigonal–bipyramidal and square-pyramidal geometries. In contrast, the corresponding adducts of the diprotonated ligands to NiII, namely tri­aqua­(4-chloro­pyridine-2,6-di­carboxyl­ato)nickel(II), [Ni(C7H2ClNO4)(H2O)3] or [NiLig2(OH2)3)], (5), and tri­aqua­(4-hy­droxy­pyridine-2,6-di­carboxyl­ato)nickel(II) 1.7-hydrate, [Ni(C7H3NO5)(H2O)3]·1.7H2O or [NiLig3(OH2)3)]·1.7H2O, (6), feature rather regular octa­hedral coordination spheres about the transition-metal cations, thus precluding the formation of analogous extended structures.

The asymmetric unit of the title compound, [Ni(C52H34Cl4N4O4)]·CH2Cl2, consists of two discrete complexes, which show significant differences in the conformation of the side chain. Each NiII cation is coordinated by four nitro­gen atoms of a porphyrin mol­ecule within a square-planar coordination environment. Weak intra­molecular C—H⋯Cl and C—H⋯O inter­actions stabilize the mol­ecular conformation. In the crystal structure, discrete complexes are linked by C—H⋯Cl hydrogen-bonding inter­actions. In addition, the two unique di­chloro­methane solvate mol­ecules (one being disordered) are hydrogen-bonded to the Cl atoms of the chloro­phenyl groups of the porphyrin mol­ecules, thus stabilizing the three-dimensional arrangement. The crystal exhibits pseudo-ortho­rhom­bic metrics, but structure refinements clearly show that the crystal system is monoclinic and that the crystal is twinned by pseudo-merohedry.

In the title compound, C20H18NO3P, the C=O and P=O groups of the carbacyl­amido­phosphate (CAPh) fragments are located in a synclinal position relative to each other and are pre-organized for bidentate chelate coordination of metal ions. The N—H group is involved in the formation of an intra­molecular hydrogen bond. In the crystal, mol­ecules do not form strong inter­molecular inter­actions but the mol­ecules are linked via weak C—H⋯π inter­actions, forming chains along [001].

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.

The crystal structure of title salt, C22H46N42+·2NO3−·2H2O, has been determined using synchrotron radiation at 220 K. The structure determination reveals that protonation has occurred at diagonally opposite amine N atoms. The asymmetric unit contains half a centrosymmetric dication, one nitrate anion and one water mol­ecule. The mol­ecular dication, C22H46N42+, together with the nitrate anion and hydrate water mol­ecule are involved in an extensive range of hydrogen bonds. The mol­ecule is stabilized, as is the conformation of the dication, by forming inter­molecular N—H⋯O, O—H⋯O, together with intra­molecular N—H⋯N hydrogen bonds.

The asymmetric unit of the title compound, [Fe(NCS)2(C12H9NO)4], consists of an FeII ion that is located on a centre of inversion, as well as two 4-benzoyl­pyridine ligands and one thio­cyanate anion in general positions. The FeII ions are coordinated by two N-terminal-bonded thio­cyanate anions and four 4-benzoyl­pyridine ligands into discrete complexes with a slightly distorted octa­hedral geometry. These complexes are further linked by weak C—H⋯O hydrogen bonds into chains running along the c-axis direction. Upon heating, this complex loses half of the 4-benzoyl­pyridine ligands and transforms into a compound with the composition Fe(NCS)2(4-benzoyl­pyridine)2, that might be isotypic to the corresponding MnII compound and for which the structure is unknown.

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 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.

In the title quinoline derivative, C24H19NO3, the two benzyl rings are inclined to the quinoline ring mean plane by 74.09 (8) and 89.43 (7)°, and to each other by 63.97 (10)°. The carboxyl­ate group is twisted from the quinoline ring mean plane by 32.2 (2)°. There is a short intra­molecular C—H⋯O contact forming an S(6) ring motif. In the crystal, mol­ecules are linked by bifurcated C—H,H⋯O hydrogen bonds, forming layers parallel to the ac plane. The layers are linked by C—H⋯π inter­actions, forming a supra­molecular three-dimensional structure.

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 asymmetric unit of the title compound, C15H12N2O2, contains two crystallographically independent mol­ecules in which the dihedral angles between the benzene rings in each are 13.26 (5) and 7.87 (5)°. An intra­molecular O—H⋯N hydrogen bonds results in the formation of an S(6) ring motif. In the crystal, mol­ecules are linked by weak C—H⋯O and C—H⋯N hydrogen bonds, forming layers parallel to (011). In addition, π–π stacking inter­actions with centroid–centroid distances in the range 3.693 (2)–3.931 (2) Å complete the three-dimensional network.

The structures of two isomers of the title compound, [RuCl2(C14H12N4)(C2H6OS)2], 2 and 3, are reported. Isomers 2 and 3 are produced by reaction of the pyridyl­triazole ligand 1-benzyl-4-(pyridin-2-yl)-1H-1,2,3-triazole (bpt) (1) with fac-[RuCl2(DMSO-S)3(DMSO-O)]. Reaction in acetone produces ca 95% 2, which is the OC-6-14 isomer, with cis DMSO and trans chlorido ligands, and 5% 3 (the OC-6-32 isomer, with cis DMSO and cis chlorido ligands, and the pyridyl moiety of bpt trans to DMSO). Reaction in refluxing toluene initially forms 2, which slowly isomerizes to 3.

The asymmetric units of the title compounds, trans-di­aqua­(3-benzyl-1,3,5,8,12-penta­aza­cyclo­tetra­decane-κ4N1,N5,N8,N12)copper(II) isophthalate monohydrate, [Cu(C16H29N5)(H2O)2](C8H4O4)·H2O, (I), and trans-di­aqua­[3-(pyridin-3-ylmeth­yl)-1,3,5,8,12-penta­aza­cyclo­tetra­decane-κ4N1,N5,N8,N12]copper(II) iso­phthalate 0.9-hydrate, [Cu(C15H28N6)(H2O)2](C8H4O4)·0.9H2O, (II) consist of one di­aqua macrocyclic cation, one di­carboxyl­ate anion and uncoordinated water mol­ecule(s). In each compound, the metal ion is coordinated by the four secondary N atoms of the macrocyclic ligand and the mutually trans O atoms of the water mol­ecules in a tetra­gonally distorted octa­hedral geometry. The average equatorial Cu—N bond lengths are significantly shorter than the average axial Cu—O bond lengths [2.020 (9) versus 2.495 (12) Å and 2.015 (4) versus 2.507 (7) Å for (I) and (II), respectively]. The coordinated macrocyclic ligand in the cations of both compounds adopts the most energetically favorable trans-III conformation. In the crystals, the complex cations and counter-anions are connected via hydrogen-bonding inter­actions between the N—H groups of the macrocycles and the O—H groups of coordinated water mol­ecules as the proton donors and the O atoms of the carboxyl­ate as the proton acceptors. Additionally, as a result of O—H⋯O hydrogen bonding with the coordinated and water mol­ecules of crystallization, the isophthalate dianions form layers lying parallel to the (overline{1}01) and (100) planes in (I) and (II), respectively.

The title pyridazin-3(2H)-one derivative, C25H19FN2O2, crystallizes with two independent mol­ecules (A and B) in the asymmetric unit. In mol­ecule A, the 4-fluoro­phenyl ring, the benzyl ring and the phenyl ring are inclined to the central pyridazine ring by 86.54 (11), 3.70 (9) and 84.857 (13)°, respectively. In mol­ecule B, the corresponding dihedral angles are 86.80 (9), 10.47 (8) and 82.01 (10)°, respectively. In the crystal, the A mol­ecules are linked by pairs of C—H⋯F hydrogen bonds, forming inversion dimers with an R22(28) ring motif. The dimers are linked by C—H⋯O hydrogen bonds and a C—H⋯π inter­action, forming columns stacking along the a-axis direction. The B mol­ecules are linked to each other in a similar manner and form columns separating the columns of A mol­ecules.

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 title mol­ecule crystallizes as a di­methyl­formamide monosolvate, C19H14N2O6S2·C3H7NO. The mol­ecule was expected to adopt mirror symmetry but slightly different conformational characteristics of the condensed benzo­thia­zine ring lead to point group symmetry 1. In the crystal, mol­ecules form two types of stacking dimers with distances of 3.464 (2) Å and 3.528 (2) Å between π-systems. As a result, columns extending parallel to [100] are formed, which are connected to inter­mediate di­methyl­formamide solvent mol­ecules by C—H⋯O inter­actions.

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.

Two CuII complexes [Cu(C14H13N4O2)Cl]n, I, and [Cu4(C8H10NO2)4Cl4]n, II, have been synthesized. In the structure of the mononuclear complex I, each ligand is coordinated to two metal centers. The basal plane around the CuII cation is formed by one chloride anion, one oxygen atom, one imino and one pyridine nitro­gen atom. The apical position of the distorted square-pyramidal geometry is occupied by a pyridine nitro­gen atom from a neighbouring unit, leading to infinite one-dimensional polymeric chains along the b-axis direction. Each chain is connected to adjacent chains by inter­molecular C—H⋯O and C—H⋯Cl inter­actions, leading to a three-dimensional network structure. The tetra­nuclear complex II lies about a crystallographic inversion centre and has one core in which two CuII metal centers are mutually inter­connected via two enolato oxygen atoms while the other two CuII cations are linked by a chloride anion and an enolato oxygen. An open-cube structure is generated in which the two open-cube units, with seven vertices each, share a side composed of two CuII ions bridged by two enolato oxygen atoms acting in a μ3-mode. The CuII atoms in each of the two CuO3NCl units are connected by one μ2-O and two μ3-O atoms from deprotonated hydroxyl groups and one chloride anion to the three other CuII centres. Each of the penta­coordinated CuII cations has a distorted NO3Cl square-pyramidal environment. The CuII atoms in each of the two CuO2NCl2 units are connected by μ2-O and μ3-O atoms from deprotonated alcohol hy­droxy groups and one chloride anion to two other CuII ions. Each of the penta­coordinated CuII cations has a distorted NO2Cl2 square-pyramidal environment. In the crystal, a series of intra­molecular C—H⋯O and C—H⋯Cl hydrogen bonds are observed in each tetra­nuclear monomeric unit, which is connected to four tetra­nuclear monomeric units by inter­molecular C—H⋯O hydrogen bonds, thus forming a planar two-dimensional structure in the (overline{1}01) plane.

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.

The asymmetric unit of the title compound, C15H21N3OS, comprises of two crystallographically independent mol­ecules (A and B). Each mol­ecule consists of a cyclo­hexane ring and a 2-hy­droxy-3-methyl­benzyl­idene ring bridged by a hydrazinecarbo­thio­amine unit. Both mol­ecules exhibit an E configuration with respect to the azomethine C=N bond. There is an intra­molecular O—H⋯N hydrogen bond in each mol­ecule forming an S(6) ring motif. The cyclo­hexane ring in each mol­ecule has a chair conformation. The benzene ring is inclined to the mean plane of the cyclo­hexane ring by 47.75 (9)° in mol­ecule A and 66.99 (9)° in mol­ecule B. The mean plane of the cyclo­hexane ring is inclined to the mean plane of the thio­urea moiety [N—C(=S)—N] by 55.69 (9) and 58.50 (8)° in mol­ecules A and B, respectively. In the crystal, the A and B mol­ecules are linked by N—H⋯S hydrogen bonds, forming `dimers'. The A mol­ecules are further linked by a C—H⋯π inter­action, hence linking the A–B units to form ribbons propagating along the b-axis direction. The conformation of a number of related cyclo­hexa­nehydrazinecarbo­thio­amides are compared to that of the title compound.

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.

The title compound, C12H21NO7, (I), is conformationally unstable; the predominant form present in its solution is the β-pyran­ose form (74.3%), followed by the β- and α-furan­oses (12.1 and 10.2%, respectively), α-pyran­ose (3.4%), and traces of the acyclic carbohydrate tautomer. In the crystalline state, the carbohydrate part of (I) adopts the 2C5 β-pyran­ose conformation, and the amino acid portion exists as a zwitterion, with the side chain cyclo­pentane ring assuming the E9 envelope conformation. All heteroatoms are involved in hydrogen bonding that forms a system of anti­parallel infinite chains of fused R33(6) and R33(8) rings. The mol­ecule features extensive intra­molecular hydrogen bonding, which is uniquely multicentered and involves the carboxyl­ate, ammonium and carbohydrate hy­droxy groups. In contrast, the contribution of inter­molecular O⋯H/H⋯O contacts to the Hirshfeld surface is relatively low (38.4%), as compared to structures of other d-fructose-amino acids. The 1H NMR data suggest a slow rotation around the C1—C2 bond in (I), indicating that the intra­molecular heteroatom contacts survive in aqueous solution of the mol­ecule as well.

The asymmetric unit of the title compound, [Zn(C6H8N4B)2(C12H8N2)], comprises one half of a ZnII cation (site symmetry 2), one di­hydro­bis­(pyrazol-1-yl)borate ligand in a general position, and one half of a phenanthroline ligand, the other half being completed by twofold rotation symmetry. The ZnII cation is coordinated in form of a slightly distorted octa­hedron by the N atoms of a phenanthroline ligand and by two pairs of N atoms of symmetry-related di­hydro­bis­(pyrazol-1-yl)borate ligands. The discrete complexes are arranged into columns that elongate in the c-axis direction with a parallel alignment of the phenanthroline ligands, indicating weak π–π inter­actions.

In the title metal–organic framework, [Fe(C6H8N2)2{Cu(CN)2}2]n, the low-spin FeII ion lies at an inversion centre and displays an elongated octa­hedral [FeN6] coordination environment. The axial positions are occupied by two symmetry-related bridging 2-ethyl­pyrazine ligands, while the equatorial positions are occupied by four N atoms of two pairs of symmetry-related cyanide groups. The CuI centre is coordinated by three cyanide carbon atoms and one N atom of a bridging 2-ethyl­pyrazine mol­ecule, which form a tetra­hedral coordination environment. Two neighbouring Cu atoms have a short Cu⋯Cu contact [2.4662 (7) Å] and their coordination tetra­hedra are connected through a common edge between two C atoms of cyanide groups. Each Cu2(CN)2 unit, formed by two neighbouring Cu atoms bridged by two carbons from a pair of μ-CN groups, is connected to six FeII centres via two bridging 2-ethyl­pyrazine mol­ecules and four cyanide groups, resulting in the formation of a polymeric three-dimensional metal–organic coordination framework.

Phenanthroline ligands are important metal-binding mol­ecules which have been extensively researched for applications in both material science and medicinal chemistry. Azo­benzene and its derivatives have received significant attention because of their ability to be reversibly switched between the E and Z forms and so could have applications in optical memory and logic devices or as mol­ecular machines. Herein we report the formation and crystal structure of a highly unusual novel diazo-diphenanthroline compound, C24H14N6O2·2CHCl3.

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.

In the title polymeric complex, {[Fe(CN)2(C10H8N2)2(H2O)2][Au(CN)2]}n, the FeII ion, which is located on a twofold rotation axis, has a slightly distorted FeN4O2 octa­hedral geometry. It is coordinated by two phenyl­pyrazine mol­ecules, two water mol­ecules and two di­cyano­aurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated di­cyano­aurate anions bridge the FeII ions to form polymeric chains propagating along the b-axis direction. In the crystal, the chains are linked by Owater—H⋯Ndi­cyano­aurate anions hydrogen bonds and aurophillic inter­actions [Au⋯Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π–π stacking inter­actions [inter­centroid distance = 3.643 (3) Å], forming a supra­molecular metal–organic framework.

The heterobifunctional organic ligand, 3-(1,2,4-triazol-4-yl)adamantane-1-carboxyl­ate (tr-ad-COO−), was employed for the synthesis of the title silver(I) coordination polymer, {[Ag(C13H16N3O2)]·2H2O}n, crystallizing in the rare ortho­rhom­bic C2221 space group. Alternation of the double μ2-1,2,4-triazole and μ2-η2:η1-COO− (chelating, bridging mode) bridges between AgI cations supports the formation of sinusoidal coordination chains. The AgI centers possess a distorted {N2O3} square-pyramidal arrangement with τ5 = 0.30. The angular organic linkers connect the chains into a tetra­gonal framework with small channels along the c-axis direction occupied by water mol­ecules of crystallization, which are inter­linked via O—H⋯O hydrogen bonds with carboxyl­ate groups, leading to right- and left-handed helical dispositions.

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.

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.

The monocation product of the oxidative condensation–cyclization between two mol­ecules of pyridine-2-carbaldehyde and one mol­ecule of CH3NH2·HCl in methanol, 2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridinium, was isolated in the presence of metal ions as bis­[2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridin-2-ium] tetra­iodo­cadmate, (C13H12N3)2[CdI4], (I), and the mixed chloride/nitrate salt, bis­[2-methyl-3-(pyridin-2-yl)imidazo[1,5-a]pyridin-2-ium] 1.5-chlor­ide 0.5-nitrate trihydrate, 2C13H12N3+·1.5Cl−·0.5NO3−·3H2O, (II). Hybrid salt (I) crystallizes in the space group P21/n with two [L]2[CdI4] mol­ecules in the asymmetric unit related by pseudosymmetry. In the crystal of (I), layers of organic cations and of tetra­halometallate anions are stacked parallel to the ab plane. Anti­parallel L+ cations disposed in a herring-bone pattern form π-bonded chains through aromatic stacking. In the inorganic layer, adjacent tetra­hedral CdI4 units have no connectivity but demonstrate close packing of iodide anions. In the crystal lattice of (II), the cations are arranged in stacks propagating along the a axis; the one-dimensional hydrogen-bonded polymer built of chloride ions and water mol­ecules runs parallel to a column of stacked cations.

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).

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 benzohydrazide derivative, C14H12N2O4, the azomethine C=N double bond has an E configuration. The hydrazide connecting bridge, (C=O)—(NH)—N=(CH), is nearly planar with C—C—N—N and C—N—N=C torsion angles of −177.33 (10) and −174.98 (12)°, respectively. The 4-hy­droxy­phenyl and 3,4-di­hydroxy­phenyl rings are slightly twisted, making a dihedral angle of 9.18 (6)°. In the crystal, mol­ecules are connected by N—H⋯O and O—H⋯O hydrogen bonds into a three-dimensional network, while further consolidated via π–π inter­actions [centroid–centroid distances = 3.6480 (8) and 3.7607 (8) Å]. The conformation is compared to those of related benzyl­idene-4-hy­droxy­benzohydrazide derivatives.