The hydrogen‐bonded complex bis(tert‐butylammonium) 2,6‐dichlorophenolate 2,4‐dichlorophenol–2,4‐dichlorophenolate tetrahydrofuran disolvate containing a chiral R53(10) hydrogen‐bonded ring as a supramolecular synthon

A fixed hydrogen‐bonding motif with a high probability of occurring when appropriate functional groups are involved is described as a `supramolecular hydrogen‐bonding synthon'. The identification of these synthons may enable the prediction of accurate crystal structures. The rare chiral hydrogen‐bonding motif R₅³(10) was observed previously in a cocrystal of 2,4,6‐trichlorophenol, 2,4‐dichlorophenol and dicyclohexylamine. In the title solvated salt, 2C₄H₁₂N⁺·C₆H₃Cl₂O⁻·(C₆H₃Cl₂O⁻·C₆H₄Cl₂O)·2C₄H₈O, five components, namely two tert‐butylammonium cations, one 2,4‐dichlorophenol molecule, one 2,4‐dichlorophenolate anion and one 2,6‐dichlorophenolate anion, are bound by N—H…O and O—H…O hydrogen bonds to form a hydrogen‐bonded ring, with the graph‐set motif R₅³(10), which is further associated with two pendant tetrahydrofuran molecules by N—H…O hydrogen bonds. The hydrogen‐bonded ring has internal symmetry, with a twofold axis running through the centre of the 2,6‐dichlorophenolate anion, and is isostructural with a previous and related structure formed from 2,4‐dichlorophenol, dicyclohexylamine and 2,4,6‐trichlorophenol. In the title crystal, helical columns are built by the alignment and twisting of the chiral hydrogen‐bonded rings, along and across the c axis, and successive pairs of rings are associated with each other through C—H…π interactions. Neighbouring helical columns are inversely related and, therefore, no chirality is sustained, in contrast to the previous case.     

Pseudopolymorphs of 2,6‐diaminopyrimidin‐4‐one and 2‐amino‐6‐methylpyrimidin‐4‐one: one or two tautomers present in the same crystal

The derivatives of pyrimidin‐4‐one can adopt either a 1H‐ or a 3H‐tautomeric form, which affects the hydrogen‐bonding interactions in cocrystals with compounds containing complementary functional groups. In order to study their tautomeric preferences, we crystallized 2,6‐diaminopyrimidin‐4‐one and 2‐amino‐6‐methylpyrimidin‐4‐one. During various crystallization attempts, four structures of 2,6‐diaminopyrimidin‐4‐one were obtained, namely solvent‐free 2,6‐diaminopyrimidin‐4‐one, C₄H₆N₄O, (I), 2,6‐diaminopyrimidin‐4‐one–dimethylformamide–water (3/4/1), C₄H₆N₄O·1.33C₃H₇NO·0.33H₂O, (Ia), 2,6‐diaminopyrimidin‐4‐one dimethylacetamide monosolvate, C₄H₆N₄O·C₄H₉NO, (Ib), and 2,6‐diaminopyrimidin‐4‐one–N‐methylpyrrolidin‐2‐one (3/2), C₄H₆N₄O·1.5C₅H₉NO, (Ic). The 2,6‐diaminopyrimidin‐4‐one molecules exist only as 3H‐tautomers. They form ribbons characterized by R²₂(8) hydrogen‐bonding interactions, which are further connected to form three‐dimensional networks. An intermolecular N—H...N interaction between amine groups is observed only in (I). This might be the reason for the pyramidalization of the amine group. Crystallization experiments on 2‐amino‐6‐methylpyrimidin‐4‐one yielded two isostructural pseudopolymorphs, namely 2‐amino‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐6‐methylpyrimidin‐4(1H)‐one–dimethylacetamide (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₄H₉NO, (IIa), and 2‐amino‐6‐methylpyrimidin‐4(3H)‐one–2‐amino‐6‐methylpyrimidin‐4(1H)‐one–N‐methylpyrrolidin‐2‐one (1/1/1), C₅H₇N₃O·C₅H₇N₃O·C₅H₉NO, (IIb). In both structures, a 1:1 mixture of 1H‐ and 3H‐tautomers is present, which are linked by three hydrogen bonds similar to a Watson–Crick C–G base pair.     

Neutral 4‐phenyl‐1‐[phenyl(pyridin‐2‐yl)methylidene]semicarbazide and its salt forms with inorganic anions

Semicarbazones can exist in two tautomeric forms. In the solid state, they are found in the keto form. This work presents the synthesis, structures and spectroscopic characterization (IR and NMR spectroscopy) of four such compounds, namely the neutral molecule 4‐phenyl‐1‐[phenyl(pyridin‐2‐yl)methylidene]semicarbazide, C₁₉H₁₆N₄O, (I), abbreviated as HBzPyS, and three different hydrated salts, namely the chloride dihydrate, C₁₉H₁₇N₄O⁺·Cl^?·2H₂O, (II), the nitrate dihydrate, C₁₉H₁₇N₄O⁺·NO₃^?·2H₂O, (III), and the thiocyanate 2.5‐hydrate, C₁₉H₁₇N₄O⁺·SCN^?·2.5H₂O, (IV), of 2‐[phenyl({[(phenylcarbamoyl)amino]imino})methyl]pyridinium, abbreviated as [H₂BzPyS]⁺·X^?·nH₂O, with X = Cl^? and n = 2 for (II), X = NO₃^? and n = 2 for (III), and X = SCN^? and n = 2.5 for (IV), showing the influence of the anionic form in the intermolecular interactions. Water molecules and counter‐ions (chloride or nitrate) are involved in the formation of a two‐dimensional arrangement by the establishment of hydrogen bonds with the N—H groups of the cation, stabilizing the E isomers in the solid state. The neutral HBzPyS molecule crystallized as the E isomer due to the existence of weak π–π interactions between pairs of molecules. The calculated IR spectrum of the hydrated [H₂BzPyS]⁺ cation is in good agreement with the experimental results.     

Cocrystals of 6‐methyl‐2‐thiouracil: presence of the acceptor–donor–acceptor/donor–acceptor–donor synthon

The results of seven cocrystallization experiments of the antithyroid drug 6‐methyl‐2‐thiouracil (MTU), C₅H₆N₂OS, with 2,4‐diaminopyrimidine, 2,4,6‐triaminopyrimidine and 6‐amino‐3H‐isocytosine (viz. 2,6‐diamino‐3H‐pyrimidin‐4‐one) are reported. MTU features an ADA (A = acceptor and D = donor) hydrogen‐bonding site, while the three coformers show complementary DAD hydrogen‐bonding sites and therefore should be capable of forming an ADA/DAD N—H...O/N—H...N/N—H...S synthon with MTU. The experiments yielded one cocrystal and six cocrystal solvates, namely 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–1‐methylpyrrolidin‐2‐one (1/1/2), C₅H₆N₂OS·C₄H₆N₄·2C₅H₉NO, (I), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine (1/1), C₅H₆N₂OS·C₄H₆N₄, (II), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–N,N‐dimethylacetamide (2/1/2), 2C₅H₆N₂OS·C₄H₆N₄·2C₄H₉NO, (III), 6‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–N,N‐dimethylformamide (2/1/2), C₅H₆N₂OS·0.5C₄H₆N₄·C₃H₇NO, (IV), 2,4,6‐triaminopyrimidinium 6‐methyl‐2‐thiouracilate–6‐methyl‐2‐thiouracil–N,N‐dimethylformamide (1/1/2), C₄H₈N₅⁺·C₅H₅N₂OS⁻·C₅H₆N₂OS·2C₃H₇NO, (V), 6‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–N,N‐dimethylformamide (1/1/1), C₅H₆N₂OS·C₄H₆N₄O·C₃H₇NO, (VI), and 6‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–dimethyl sulfoxide (1/1/1), C₅H₆N₂OS·C₄H₆N₄O·C₂H₆OS, (VII). Whereas in cocrystal (I) an R₂²(8) interaction similar to the Watson–Crick adenine/uracil base pair is formed and a two‐dimensional hydrogen‐bonding network is observed, the cocrystals (II)–(VII) contain the triply hydrogen‐bonded ADA/DAD N—H...O/N—H...N/N—H...S synthon and show a one‐dimensional hydrogen‐bonding network. Although 2,4‐diaminopyrimidine possesses only one DAD hydrogen‐bonding site, it is, due to orientational disorder, triply connected to two MTU molecules in (III) and (IV).     

New pseudopolymorphs of 5‐fluorocytosine

In order to better understand the interaction between the pharmaceutically active compound 5‐fluorocytosine [4‐amino‐5‐fluoropyrimidin‐2(1H)‐one] and its receptor, hydrogen‐bonded complexes with structurally similar bonding patterns have been investigated. During the cocrystallization screening, three new pseudopolymorphs of 5‐fluorocytosine were obtained, namely 5‐fluorocytosine dimethyl sulfoxide solvate, C₄H₄FN₃O·C₂H₆OS, (I), 5‐fluorocytosine dimethylacetamide hemisolvate, C₄H₄FN₃O·0.5C₄H₉NO, (II), and 5‐fluorocytosine hemihydrate, C₄H₄FN₃O·0.5H₂O, (III). Similar hydrogen‐bond patterns are observed in all three crystal structures. The 5‐fluorocytosine molecules form ribbons with repeated R₂²(8) dimer interactions. These dimers are stabilized by N—H...N and N—H...O hydrogen bonds. The solvent molecules adopt similar positions with respect to 5‐fluorocytosine. Depending on the hydrogen bonds formed by the solvent, the 5‐fluorocytosine ribbons form layers or tubes. A database study was carried out to compare the hydrogen‐bond pattern of compounds (I)–(III) with those of other (pseudo)polymorphs of 5‐fluorocytosine.     

Supramolecular hydrogen‐bonded networks in cytosinium succinate and cytosinium 4‐nitrobenzoate cytosine monohydrate

In cytosinium succinate (systematic name: 4‐amino‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium 3‐carboxypropanoate), C₄H₆N₃O⁺·C₄H₅O₄⁻, (I), the cytosinium cation forms one‐dimensional self‐assembling patterns by intermolecular N—H...O hydrogen bonding, while in cytosinium 4‐nitrobenzoate cytosine monohydrate [systematic name: 4‐amino‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium 4‐nitrobenzoate 4‐aminopyrimidin‐2(1H)‐one solvate monohydrate], C₄H₆N₃O⁺·C₇H₄NO₄⁻·C₄H₅N₃O·H₂O, (II), the cytosinium–cytosine base pair, held together by triple hydrogen bonds, leads to one‐dimensional polymeric ribbons via double N—H...O hydrogen bonds. This study illustrates clearly the different alignment of cytosine molecules in the crystal packing and their ability to form supramolecular hydrogen‐bonded networks with the anions.     

Two phosphonodehydrotripeptides: Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2 and Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2

The present paper reports the crystal structures of two short phosphonotripeptides (one in two crystal forms) containing one ΔPhe (dehydrophenylalanine) residue, namely dimethyl (3‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}propyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Abu³PO₃Me₂, C₂₁H₃₂N₃O₇P, (I), and diethyl (4‐{[tert‐butoxycarbonylglycyl‐α,β‐(Z)‐dehydrophenylalanyl]amino}butyl)phosphonate, Boc⁰–Gly¹–Δ(Z)Phe²–α‐Nva³PO₃Et₂, as the propan‐2‐ol monosolvate 0.122‐hydrate, C₂₄H₃₈N₃O₇P·C₃H₈O·0.122H₂O, (II), and the ethanol monosolvate 0.076‐hydrate, C₂₄H₃₈N₃O₇P·C₂H₆O·0.076H₂O, (III). The crystals of (II) and (III) are isomorphous but differ in the type of solvent. The phosphono group is linked directly to the last C_α atom in the main chain for all three peptides. All the amino acids are trans linked in the main chains. The crystal structures exhibit no intramolecular hydrogen bonds and are stabilized by intermolecular hydrogen bonds only.     

Two hydration products of 3,4,5,6‐tetrachloro‐N‐(methyl‐2‐pyridyl)phthalmic acids

In 2‐amino‐6‐methylpyridin‐1‐ium 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate, C₆H₉N₂⁺·C₈HCl₄O₄⁻, there are two perpendicular chains of hydrogen‐bonded ions, one arising from the interaction between 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate ions and the other from the interaction between the 2‐amino‐6‐methylpyridin‐1‐ium and 2‐carboxy‐3,4,5,6‐tetrachlorobenzoate ions. These chains combine to form a two‐dimensional network of hydrogen‐bonded ions. Cocrystals of bis(2‐amino‐3‐methylpyridin‐1‐ium) 3,4,5,6‐tetrachlorophthalate–3,4,5,6‐tetrachlorophthalic acid (1/1), 2C₆H₉N₂⁺·C₈Cl₄O₄²⁻·C₈H₂Cl₄O₄, form finite aggregates of hydrogen‐bonded ions. π–π interactions are observed between 2‐amino‐3‐methylpyridin‐1‐ium cations. Both structures exhibit the characteristic R₂²(8) motif as a result of the hydrogen bonding between the 2‐aminopyridinium and carboxylate units.     

Comparison of the hydrogen‐bond patterns in 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1) and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1)

The X‐ray single‐crystal structure determinations of the chemically related compounds 2‐amino‐1,3,4‐thiadiazolium hydrogen oxalate, C₂H₄N₃S⁺·C₂HO₄⁻, (I), 2‐amino‐1,3,4‐thiadiazole–succinic acid (1/2), C₂H₃N₃S·2C₄H₆O₄, (II), 2‐amino‐1,3,4‐thiadiazole–glutaric acid (1/1), C₂H₃N₃S·C₅H₈O₄, (III), and 2‐amino‐1,3,4‐thiadiazole–adipic acid (1/1), C₂H₃N₃S·C₆H₁₀O₄, (IV), are reported and their hydrogen‐bonding patterns are compared. The hydrogen bonds are of the types N—H...O or O—H...N and are of moderate strength. In some cases, weak C—H...O interactions are also present. Compound (II) differs from the others not only in the molar ratio of base and acid (1:2), but also in its hydrogen‐bonding pattern, which is based on chain motifs. In (I), (III) and (IV), the most prominent feature is the presence of an R₂²(8) graph‐set motif formed by N—H...O and O—H...N hydrogen bonds, which are present in all structures except for (I), where only a pair of N—H...O hydrogen bonds is present, in agreement with the greater acidity of oxalic acid. There are nonbonding S...O interactions present in all four structures. The difference electron‐density maps show a lack of electron density about the S atom along the S...O vector. In all four structures, the carboxylic acid H atoms are present in a rare configuration with a C—C—O—H torsion angle of ∼0°. In the structures of (II)–(IV), the C—C—O—H torsion angle of the second carboxylic acid group has the more common value of ∼|180|°. The dicarboxylic acid molecules are situated on crystallographic inversion centres in (II). The Raman and IR spectra of the title compounds are presented and analysed.     

Cocrystallization of two tautomers: 4‐(1‐{[4‐(dimethylamino)benzylidene]hydrazono}ethyl)benzene‐1,3‐diol and 6‐[(E)‐1‐{[4‐(dimethylamino)benzylidene]hydrazino}ethylidene]‐3‐hydroxycyclohexa‐2,4‐dien‐1‐one (1/1)

Two different tautomeric forms of a new Schiff base, C₁₇H₁₉N₃O₂·C₁₇H₁₉N₃O₂, are present in the crystal in a 1:1 ratio, namely the enol–imine form 4‐(1‐{[4‐(dimethylamino)benzylidene]hydrazono}ethyl)benzene‐1,3‐diol and the keto–amine form 6‐[(E)‐1‐{[4‐(dimethylamino)benzylidene]hydrazino}ethylidene]‐3‐hydroxycyclohexa‐2,4‐dien‐1‐one. The tautomers are formed by proton transfer between the hydroxy O atom and the imine N atom and are hydrogen bonded to each other to form a one‐dimensional zigzag chain along the crystallographic b axis via intermolecular hydrogen bonds.     

Hydrogen‐bonded networks in trans‐3‐(3‐pyridyl)acrylic acid and rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride

The structure of trans‐3‐(3‐pyridyl)acrylic acid, C₈H₇NO₂, (I), possesses a two‐dimensional hydrogen‐bonded array of supramolecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring molecules [3.821 (1) Å] along the a axis. The crystal structure of the photoproduct, rctt‐3,3′‐(3,4‐dicarboxycyclobutane‐1,2‐diyl)dipyridinium dichloride, C₁₆H₁₆N₂O₄²⁺·2Cl⁻, (II), consists of a three‐dimensional hydrogen‐bonded network built from crosslinking of helical chains integrated by self‐assembly of dipyridinium cations and Cl⁻ anions via different O—H...Cl, C—H...Cl and N⁺—H...Cl hydrogen‐bond interactions.     

Z and E isomers of butenedioic acid with 2‐amino‐1,3‐thiazole: 2‐amino‐1,3‐thiazolium hydrogen maleate and 2‐amino‐1,3‐thiazolium hydrogen fumarate

Maleic acid and fumaric acid, the Z and E isomers of butenedioic acid, form 1:1 adducts with 2‐amino‐1,3‐thiazole, namely 2‐amino‐1,3‐thiazolium hydrogen maleate (2ATHM), C₃H₅N₂S⁺·C₄H₃O₄⁻, and 2‐amino‐1,3‐thiazolium hydrogen fumarate (2ATHF), C₃H₅N₂S⁺·C₄H₃O₄⁻, respectively. In both compounds, protonation of the ring N atom of the 2‐amino‐1,3‐thiazole and deprotonation of one of the carboxyl groups are observed. The asymmetric unit of 2ATHF contains three independent ion pairs. The hydrogen maleate ion of 2ATHM shows a short intramolecular O—H...O hydrogen bond with an O...O distance of 2.4663 (19) Å. An extensive hydrogen‐bonded network is observed in both compounds, involving N—H...O and O—H...O hydrogen bonds. 2ATHM forms two‐dimensional sheets parallel to the ab plane, extending as independent parallel sheets along the c axis, whereas 2ATHF forms two‐dimensional zigzag layers parallel to the bc plane, extending as independent parallel layers along the a axis.     

4‐(4‐Hydro­xy­benzyl­idene­amino)‐4H‐1,2,4‐triazole hemihydrate

In the title compound, 4‐(4H‐1,2,4‐triazol‐4‐yl­imino­methyl)­phenol hemi­hydrate, C₉H₈N₄O·0.5H₂O or (I)·0.5H₂O, mol­ecules of (I) are arranged as layers running along the b axis through intermolecular O—H?N and C—H?O hydrogen bonds. These layers are stabilized by hydrogen‐bonded water mol­ecules to form three‐dimensional networks.     

A fourfold interpenetrating diamondoid three‐dimensional coordination polymer: poly[[[μ2‐1,2‐bis(pyridin‐4‐yl)ethene‐κ2N:N′](μ2‐5‐hydroxyisophthalato‐κ2O1:O3)zinc(II)] 1,2‐bis(pyridin‐4‐yl)ethene hemisolvate]

In the title compound, {[Zn(C₈H₄O₅)(C₁₂H₁₀N₂)]·0.5C₁₂H₁₀N₂}_n or {[Zn(HO‐BDC)(bpe)]·0.5bpe}_n [HO‐H₂BDC is 5‐hydroxyisophthalic acid and bpe is 1,2‐bis(pyridin‐4‐yl)ethene], the asymmetric unit contains a Zn^II atom, one HO‐BDC ligand, one coordinated bpe ligand and half a noncoordinating bpe molecule with crystallographic inversion symmetry. Each Zn^II centre is four‐coordinated by two O atoms from two distinct HO‐BDC ligands and two N atoms from two different bpe ligands in a ZnO₂N₂ coordination environment. The three‐dimensional topology of the title compound corresponds to a fourfold interpenetrating diamondoid coordination polymer network, with the uncoordinated bpe ligands located in the cavities, hydrogen bonded to the main network via the hydroxy group of the HO‐H₂BDC ligand.     

Influence of solvent on the structures of two one‐dimensional cobalt(II) coordination polymers with tetrachloroterephthalate

The title cobalt coordination polymers, catena‐poly[[[aquatripyridinecobalt(II)]‐μ‐tetrachloroterephthalato] pyridine solvate], {[Co(C₈Cl₄O₄)(C₅H₅N)₃(H₂O)]·C₅H₅N}_n, (I), and catena‐poly[[[diaquadipyridinecobalt(II)]‐μ‐tetrachloroterephthalato] 1,4‐dioxane trihydrate], {[Co(C₈Cl₄O₄)(C₅H₅N)₂(H₂O)₂]·C₄H₈O₂·3H₂O}_n, (II), have been prepared with tetrachloroterephthalic acid (H₂BDC‐Cl₄) under different solvent media. Both complexes form infinite cobalt(II)–tetrachloroterephthalate polymeric chains. In (I), two independent Co^II ions are six‐coordinated through N₃O₃ donor sets in slightly distorted octahedral geometries provided by two carboxylate and three pyridine ligands, and one water molecule. The structure of (II) contains two independent Co^II atoms, each lying on a twofold axis, which adopt a tetragonally distorted N₂O₄ octahedral geometry via two carboxylate groups, two pyridine ligands and two water molecules. The different stoichiometry of coordinated and solvent guest molecules leads to different two‐dimensional supramolecular networks, with (I) utilizing C—H...π and weak π–π interactions and (II) utilizing mainly conventional hydrogen bonding.     

3,5‐Bis{4‐[(benzimidazol‐1‐yl)methyl]phenyl}‐4H‐1,2,4‐triazol‐4‐amine and its one‐dimensional polymeric complex with HgCl2

The molecule of 3,5‐bis{4‐[(benzimidazol‐1‐yl)methyl]phenyl}‐4H‐1,2,4‐triazol‐4‐amine (L), C₃₀H₂₄N₈, has an antiperiplanar conformation of the two terminal benzimidazole groups and forms two‐dimensional networks along the crystallographic b axis via two types of intermolecular hydrogen bonds. However, in catena‐poly[[[dichloridomercury(II)]‐μ‐3,5‐bis{4‐[(benzimidazol‐1‐yl)methyl]phenyl}‐4H‐1,2,4‐triazol‐4‐amine] dichloromethane hemisolvate], {[HgCl₂(C₃₀H₂₄N₈)]·0.5CH₂Cl₂}_n, synthesized by the combination of L with HgCl₂, the L ligand adopts a synperiplanar conformation. The Hg^II cation lies in a distorted tetrahedral environment, which is defined by two N atoms and two Cl atoms to form a one‐dimensional zigzag chain. These zigzag chains stack via hydrogen bonds which expand the dimensionality of the structure from one to two.     

Zero‐, one‐ and two‐dimensional hydrogen‐bonded structures in the 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid with the monocyclic heteroaromatic Lewis bases 2‐aminopyrimidine,nicotinamide and isonicotinamide

The structures of the anhydrous 1:1 proton‐transfer compounds of 4,5‐dichlorophthalic acid (DCPA) with the monocyclic heteroaromatic Lewis bases 2‐aminopyrimidine, 3‐(aminocarbonyl)pyridine (nicotinamide) and 4‐(aminocarbonyl)pyridine (isonicotinamide), namely 2‐aminopyrimidinium 2‐carboxy‐4,5‐dichlorobenzoate, C₄H₆N₃⁺·C₈H₃Cl₂O₄⁻, (I), 3‐(aminocarbonyl)pyridinium 2‐carboxy‐4,5‐dichlorobenzoate, C₆H₇N₂O⁺·C₈H₃Cl₂O₄⁻, (II), and the unusual salt adduct 4‐(aminocarbonyl)pyridinium 2‐carboxy‐4,5‐dichlorobenzoate–methyl 2‐carboxy‐4,5‐dichlorobenzoate (1/1), C₆H₇N₂O⁺·C₈H₃Cl₂O₄⁻·C₉H₆Cl₂O₄, (III), have been determined at 130 K. Compound (I) forms discrete centrosymmetric hydrogen‐bonded cyclic bis(cation–anion) units having both R₂²(8) and R₁²(4) N—H...O interactions. In (II), the primary N—H...O‐linked cation–anion units are extended into a two‐dimensional sheet structure via amide–carboxyl and amide–carbonyl N—H...O interactions. The structure of (III) reveals the presence of an unusual and unexpected self‐synthesized methyl monoester of the acid as an adduct molecule, giving one‐dimensional hydrogen‐bonded chains. In all three structures, the hydrogen phthalate anions are essentially planar with short intramolecular carboxyl–carboxylate O—H...O hydrogen bonds [O...O = 2.393 (8)–2.410 (2) Å]. This work provides examples of low‐dimensional 1:1 hydrogen‐bonded DCPA structure types, and includes the first example of a discrete cyclic `heterotetramer.' This low dimensionality in the structures of the 1:1 aromatic Lewis base salts of the parent acid is generally associated with the planar DCPA anion species.     

The honeycomb network structure of poly[[[μ2‐1,3‐bis(1H‐benzimidazol‐2‐yl)benzene‐κ2N3:N3′](μ2‐terephthalato‐κ2O:O′)zinc(II)] ethanol solvate]

The terephthalate dianion and the bis(imidazolyl)benzene ligand of the title compound, {[Zn(C₈H₄O₄)(C₂₀H₁₄N₄)]·C₂H₆O}_n, each bridges two adjacent zinc centers, resulting in a layer‐type coordination polymer; the zinc center shows tetrahedral coordination. The disordered ethanol solvent molecules occupy the spaces between the layers and are hydrogen bonded to the layers. The two symmetry‐independent dianions lie on different inversion sites.     

Isomorphism in 1‐(2‐halidobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium halide hemihydrates (halide = Cl,Br)

The crystal structures of two (E)‐stilbazolium salts, namely 1‐(2‐chlorobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium chloride hemihydrate, C₂₀H₁₇ClNO⁺·Cl⁻·0.5H₂O, (I), and 1‐(2‐bromobenzyl)‐4‐[(E)‐2‐(3‐hydroxyphenyl)ethenyl]pyridinium bromide hemihydrate, C₂₀H₁₇BrNO⁺·Br⁻·0.5H₂O, (II), are isomorphous; the isostructurality index is 99.3%. In both salts, the azastyryl fragments are almost planar, while the rings of the benzyl groups are almost perpendicular to the azastyryl planes. The building blocks of the structures are twofold symmetric hydrogen‐bonded systems of two cations, two halide anions and one water molecule, which lies on a twofold axis. In the crystal structure, these blocks are connected by means of weaker interactions, viz. van der Waals, weak hydrogen bonding and stacking. This study illustrates the robustness of certain supramolecular motifs created by a spectrum of intermolecular interactions in generating these isomorphous crystal structures.     

1‐Carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium chloride 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate monohydrate: a crystal stabilized by imidazolium zwitterions

The title compound, C₆H₉N₂O₂⁺·Cl⁻·C₆H₈N₂O₂·H₂O, contains one 2‐(3‐methyl‐1H‐imidazol‐3‐ium‐1‐yl)acetate inner salt molecule, one 1‐carboxymethyl‐3‐methyl‐1H‐imidazol‐3‐ium cation, one chloride ion and one water molecule. In the extended structure, chloride anions and water molecules are linked via O—H...Cl hydrogen bonds, forming an infinite one‐dimensional chain. The chloride anions are also linked by two weak C—H...Cl interactions to neighbouring methylene groups and imidazole rings. Two imidazolium moieties form a homoconjugated cation through a strong and asymmetric O—H...O hydrogen bond of 2.472 (2) Å. The IR spectrum shows a continuous D‐type absorption in the region below 1300 cm⁻¹ and is different to that of 1‐carboxymethyl‐3‐methylimidazolium chloride [Xuan, Wang & Xue (2012). Spectrochim. Acta Part A, 96 , 436–443].