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).     

Sulfur as hydrogen‐bond acceptor in cocrystals of 2‐thio‐modified thymine

Doubly and triply hydrogen‐bonded supramolecular synthons are of particular interest for the rational design of crystal and cocrystal structures in crystal engineering since they show a high robustness due to their high stability and good reliability. The compound 5‐methyl‐2‐thiouracil (2‐thiothymine) contains an ADA hydrogen‐bonding site (A = acceptor and D = donor) if the S atom is considered as an acceptor. We report herein the results of cocrystallization experiments with the coformers 2,4‐diaminopyrimidine, 2,4‐diamino‐6‐phenyl‐1,3,5‐triazine, 6‐amino‐3H‐isocytosine and melamine, which contain complementary DAD hydrogen‐bonding sites and, therefore, should be capable of forming a mixed ADA–DAD N—H…S/N—H…N/N—H…O synthon (denoted synthon 3s_{N·S;N·N;N·O}), consisting of three different hydrogen bonds with 5‐methyl‐2‐thiouracil. The experiments yielded one cocrystal and five solvated cocrystals, namely 5‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine (1/2), C₅H₆N₂OS·2C₄H₆N₄, (I), 5‐methyl‐2‐thiouracil–2,4‐diaminopyrimidine–N,N‐dimethylformamide (2/2/1), 2C₅H₆N₂OS·2C₄H₆N₄·C₃H₇NO, (II), 5‐methyl‐2‐thiouracil–2,4‐diamino‐6‐phenyl‐1,3,5‐triazine–N,N‐dimethylformamide (2/2/1), 2C₅H₆N₂OS·2C₉H₉N₅·C₃H₇NO, (III), 5‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–N,N‐dimethylformamide (2/2/1), (IV), 2C₅H₆N₂OS·2C₄H₆N₄O·C₃H₇NO, (IV), 5‐methyl‐2‐thiouracil–6‐amino‐3H‐isocytosine–N,N‐dimethylacetamide (2/2/1), 2C₅H₆N₂OS·2C₄H₆N₄O·C₄H₉NO, (V), and 5‐methyl‐2‐thiouracil–melamine (3/2), 3C₅H₆N₂OS·2C₃H₆N₆, (VI). Synthon 3s_{N·S;N·N;N·O} was formed in three structures in which two‐dimensional hydrogen‐bonded networks are observed, while doubly hydrogen‐bonded interactions were formed instead in the remaining three cocrystals whereby three‐dimensional networks are preferred. As desired, the S atoms are involved in hydrogen‐bonding interactions in all six structures, thus illustrating the ability of sulfur to act as a hydrogen‐bond acceptor and, therefore, its value for application in crystal engineering.     

Cocrystals of 6‐propyl‐2‐thiouracil: N—H...O versus N—H...S hydrogen bonds

In order to investigate the relative stability of N—H...O and N—H...S hydrogen bonds, we cocrystallized the antithyroid drug 6‐propyl‐2‐thiouracil with two complementary heterocycles. In the cocrystal pyrimidin‐2‐amine–6‐propyl‐2‐thiouracil (1/2), C₄H₅N₃·2C₇H₁₀N₂OS, (I), the `base pair' is connected by one N—H...S and one N—H...N hydrogen bond. Homodimers of 6‐propyl‐2‐thiouracil linked by two N—H...S hydrogen bonds are observed in the cocrystal N‐(6‐acetamidopyridin‐2‐yl)acetamide–6‐propyl‐2‐thiouracil (1/2), C₉H₁₁N₃O₂·2C₇H₁₀N₂OS, (II). The crystal structure of 6‐propyl‐2‐thiouracil itself, C₇H₁₀N₂OS, (III), is stabilized by pairwise N—H...O and N—H...S hydrogen bonds. In all three structures, N—H...S hydrogen bonds occur only within R₂²(8) patterns, whereas N—H...O hydrogen bonds tend to connect the homo‐ and heterodimers into extended networks. In agreement with related structures, the hydrogen‐bonding capability of C=O and C=S groups seems to be comparable.     

Eight new crystal structures of 5‐(hydroxymethyl)uracil, 5‐carboxyuracil and 5‐carboxy‐2‐thiouracil: insights into the hydrogen‐bonded networks and the predominant conformations of the C5‐bound residues

In order to examine the preferred hydrogen‐bonding pattern of various uracil derivatives, namely 5‐(hydroxymethyl)uracil, 5‐carboxyuracil and 5‐carboxy‐2‐thiouracil, and for a conformational study, crystallization experiments yielded eight different structures: 5‐(hydroxymethyl)uracil, C₅H₆N₂O₃, (I), 5‐carboxyuracil–N,N‐dimethylformamide (1/1), C₅H₄N₂O₄·C₃H₇NO, (II), 5‐carboxyuracil–dimethyl sulfoxide (1/1), C₅H₄N₂O₄·C₂H₆OS, (III), 5‐carboxyuracil–N,N‐dimethylacetamide (1/1), C₅H₄N₂O₄·C₄H₉NO, (IV), 5‐carboxy‐2‐thiouracil–N,N‐dimethylformamide (1/1), C₅H₄N₂O₃S·C₃H₇NO, (V), 5‐carboxy‐2‐thiouracil–dimethyl sulfoxide (1/1), C₅H₄N₂O₃S·C₂H₆OS, (VI), 5‐carboxy‐2‐thiouracil–1,4‐dioxane (2/3), 2C₅H₄N₂O₃S·3C₆H₁₂O₃, (VII), and 5‐carboxy‐2‐thiouracil, C₁₀H₈N₄O₆S₂, (VIII). While the six solvated structures, i.e. (II)–(VII), contain intramolecular S(6) O—H…O hydrogen‐bond motifs between the carboxy and carbonyl groups, the usually favoured R₂²(8) pattern between two carboxy groups is formed in the solvent‐free structure, i.e. (VIII). Further R₂²(8) hydrogen‐bond motifs involving either two N—H…O or two N—H…S hydrogen bonds were observed in three crystal structures, namely (I), (IV) and (VIII). In all eight structures, the residue at the ring 5‐position shows a coplanar arrangement with respect to the pyrimidine ring which is in agreement with a search of the Cambridge Structural Database for six‐membered cyclic compounds containing a carboxy group. The search confirmed that coplanarity between the carboxy group and the cyclic residue is strongly favoured.     

6‐Propyl‐2‐thiouracil versus 6‐methoxymethyl‐2‐thiouracil: enhancing the hydrogen‐bonded synthon motif by replacement of a methylene group with an O atom

The understanding of intermolecular interactions is a key objective of crystal engineering in order to exploit the derived knowledge for the rational design of new molecular solids with tailored physical and chemical properties. The tools and theories of crystal engineering are indispensable for the rational design of (pharmaceutical) cocrystals. The results of cocrystallization experiments of the antithyroid drug 6‐propyl‐2‐thiouracil (PTU) with 2,4‐diaminopyrimidine (DAPY), and of 6‐methoxymethyl‐2‐thiouracil (MOMTU) with DAPY and 2,4,6‐triaminopyrimidine (TAPY), respectively, are reported. PTU and MOMTU show a high structural similarity and differ only in the replacement of a methylene group (–CH₂–) with an O atom in the side chain, thus introducing an additional hydrogen‐bond acceptor in MOMTU. Both molecules contain an ADA hydrogen‐bonding site (A = acceptor and D = donor), while the coformers DAPY and TAPY both show complementary DAD sites and therefore should be capable of forming a mixed ADA/DAD synthon with each other, i.e. N—H…O, N—H…N and N—H…S hydrogen bonds. The experiments yielded one solvated cocrystal salt of PTU with DAPY, four different solvates of MOMTU, one ionic cocrystal of MOMTU with DAPY and one cocrystal salt of MOMTU with TAPY, namely 2,4‐diaminopyrimidinium 6‐propyl‐2‐thiouracilate–2,4‐diaminopyrimidine–N,N‐dimethylacetamide–water (1/1/1/1) (the systematic name for 6‐propyl‐2‐thiouracilate is 6‐oxo‐4‐propyl‐2‐sulfanylidene‐1,2,3,6‐tetrahydropyrimidin‐1‐ide), C₄H₇N₄⁺·C₇H₉N₂OS⁻·C₄H₆N₄·C₄H₉NO·H₂O, (I), 6‐methoxymethyl‐2‐thiouracil–N,N‐dimethylformamide (1/1), C₆H₈N₂O₂S·C₃H₇NO, (II), 6‐methoxymethyl‐2‐thiouracil–N,N‐dimethylacetamide (1/1), C₆H₈N₂O₂S·C₄H₉NO, (III), 6‐methoxymethyl‐2‐thiouracil–dimethyl sulfoxide (1/1), C₆H₈N₂O₂S·C₂H₆OS, (IV), 6‐methoxymethyl‐2‐thiouracil–1‐methylpyrrolidin‐2‐one (1/1), C₆H₈N₂O₂S·C₅H₉NO, (V), 2,4‐diaminopyrimidinium 6‐methoxymethyl‐2‐thiouracilate (the systematic name for 6‐methoxymethyl‐2‐thiouracilate is 4‐methoxymethyl‐6‐oxo‐2‐sulfanylidene‐1,2,3,6‐tetrahydropyrimidin‐1‐ide), C₄H₇N₄⁺·C₆H₇N₂O₂S⁻, (VI), and 2,4,6‐triaminopyrimidinium 6‐methoxymethyl‐2‐thiouracilate–6‐methoxymethyl‐2‐thiouracil (1/1), C₄H₈N₅⁺·C₆H₇N₂O₂S⁻·C₆H₈N₂O₂S, (VII). Whereas in (I) only an AA/DD hydrogen‐bonding interaction was formed, the structures of (VI) and (VII) both display the desired ADA/DAD synthon. Conformational studies on the side chains of PTU and MOMTU also revealed a significant deviation for cocrystals (VI) and (VII), leading to the desired enhancement of the hydrogen‐bond pattern within the crystal.     

Three‐dimensional networks in bis(imidazolium) 2,2′‐dithiodibenzoate and 4‐methylimidazolium 2‐[(2‐carboxyphenyl)disulfanyl]benzoate

Cocrystallization of imidazole or 4‐methylimidazole with 2,2′‐dithiodibenzoic acid from methanol solution yields the title 2:1 and 1:1 organic salts, 2C₃H₅N₂⁺·C₁₄H₁₀O₄S₂²⁻, (I), and C₄H₇N₂⁺·C₁₄H₁₀O₄S₂⁻, (II), respectively. Compound (I) crystallizes in the monoclinic C2/c space group with the mid‐point of the S—S bond lying on a twofold axis. The component ions in (I) are linked by intermolecular N—H...O hydrogen bonds to form a two‐dimensional network, which is further linked by C—H...O hydrogen bonds into a three‐dimensional network. In contrast, by means of N—H...O, N—H...S and O—H...O hydrogen bonds, the component ions in (II) are linked into a tape and adjacent tapes are further linked by π–π, C—H...O and C—H...π interactions, resulting in a three‐dimensional network.     

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.     

Supramolecular aggregation in three 4‐aryl‐6‐(1H‐indol‐3‐yl)‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitriles

Both 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile and 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methoxyphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile crystallize from dimethylformamide solutions as stoichiometric 1:1 solvates, viz. C₂₉H₂₁N₅·C₃H₇NO, (I), and C₂₉H₂₁N₅O·C₃H₇NO, (II), respectively; however, 6‐(1H‐indol‐3‐yl)‐3‐methyl‐1‐phenyl‐4‐(3,4,5‐trimethoxyphenyl)‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile, C₃₁H₂₅N₅O₃, (III), crystallizes in the unsolvated form. The heterocyclic components of (I) are linked by C—H...π(arene) hydrogen bonds to form cyclic centrosymmetric dimers, from which the solvent molecules are pendent, linked by N—H...O hydrogen bonds. In (II), the heterocyclic components are linked by a combination of C—H...N and C—H...π(arene) hydrogen bonds into chains containing two types of centrosymmetric ring, and the pendent solvent molecules are linked to these chains by N—H...O hydrogen bonds. Molecules of (III) are linked into simple C(12) chains by an N—H...O hydrogen bond, and these chains are weakly linked into pairs by an aromatic π–π stacking interaction.     

Supramolecular hydrogen‐bonding patterns in two cocrystals of the N(7)–H tautomeric form of N6‐benzoyladenine: N6‐benzoyladenine–3‐hydroxypyridinium‐2‐carboxylate (1/1) and N6‐benzoyladenine–DL‐tartaric acid (1/1)

Two novel cocrystals of the N(7)—H tautomeric form of N⁶‐benzoyladenine (BA), namely N⁶‐benzoyladenine–3‐hydroxypyridinium‐2‐carboxylate (3HPA) (1/1), C₁₂H₉N₅O·C₆H₅NO₃, (I), and N⁶‐benzoyladenine–DL‐tartaric acid (TA) (1/1), C₁₂H₉N₅O·C₄H₆O₆, (II), are reported. In both cocrystals, the N⁶‐benzoyladenine molecule exists as the N(7)—H tautomer, and this tautomeric form is stabilized by intramolecular N—H...O hydrogen bonding between the benzoyl C=O group and the N(7)—H hydrogen on the Hoogsteen site of the purine ring, forming an S(7) motif. The dihedral angle between the adenine and phenyl planes is 0.94 (8)° in (I) and 9.77 (8)° in (II). In (I), the Watson–Crick face of BA (N6—H and N1; purine numbering) interacts with the carboxylate and phenol groups of 3HPA through N—H...O and O—H...N hydrogen bonds, generating a ring‐motif heterosynthon [graph set R₂²(6)]. However, in (II), the Hoogsteen face of BA (benzoyl O atom and N7; purine numbering) interacts with TA (hydroxy and carbonyl O atoms) through N—H...O and O—H...O hydrogen bonds, generating a different heterosynthon [graph set R₂²(4)]. Both crystal structures are further stabilized by π–π stacking interactions.     

A two‐dimensional layer in N,N′‐bis[2‐(hydroxymethyl)benzyl]ethylenediamine and a three‐dimensional network in N,N′‐bis[2‐(hydroxymethyl)benzyl]ethylenediammonium bis(perchlorate)

In both title compounds, C₁₈H₂₄N₂O₂, (Ia), and C₁₈H₂₆N₂O₂²⁺·2ClO₄⁻, (II), respectively, the two aryl rings are strictly parallel, with an inversion centre lying at the mid‐point of each central CH₂—CH₂ bond. Molecules in (Ia) are linked into two‐dimensional layers by N—H...O hydrogen bonds. The component ions in (II) are joined together by a combination of N/O/C—H...O hydrogen bonds and C—H...π and anion...π interactions, forming a three‐dimensional network. A structural understanding of (Ia) and (II) may provide some useful information about how and why their metal–organic complexes display various biological activities and function in catalytic processes.     

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.     

2,4‐Diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium trifluoroacetate

Crystals of the title compound, C₄H₈N₅⁺·C₂F₃O₂⁻, are built up of singly protonated 2,4‐diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium cations and trifluoroacetate anions. The CF₃ group of the anion is disordered. The oppositely charged ions interact via almost linear N—H...O hydrogen bonds, forming a CF₃COO⁻...C₄H₈N₅⁺ unit. Two units related by an inversion centre interact through a pair of N—H...N hydrogen bonds, forming planar (CF₃COO⁻...C₄H₈N₅⁺...C₄H₈N₅⁺·CF₃COO⁻) aggregates that are linked by a pair of N—H...O hydrogen bonds into chains running along the c axis.     

catena‐Poly[[[(iminodiacetato‐κO)silver(I)]‐μ3‐2‐aminopyrimidine‐κ3N1:N2:N3] monohydrate]: a one‐dimensional silver(I) coordination polymer with mixed ligands

The title compound, {[Ag(C₄H₆NO₄)(C₄H₅N₃)]·H₂O}_n, was synthesized by the reaction of silver(I) nitrate with 2‐aminopyrimidine and iminodiacetic acid. X‐ray analysis reveals that the crystal structure contains a one‐dimensional ladder‐like Ag^I coordination polymer and that N—H...O and O—H...O hydrogen bonding results in a three‐dimensional network. The Ag^I centre is four‐coordinated by three N atoms from three different 2‐aminopyrimidine ligands and one O atom from one iminodiacetate ligand. Comparison of the structural features with previous findings suggests that the existence of a second ligand plays an important role in the construction of such polymer frameworks.     

Three‐dimensional hydrogen‐bonded framework in bis(melamin‐1‐ium) naphthalene‐1,5‐disulfonate melamine pentahydrate

Crystals of the title compound, 2C₃H₇N₆⁺·C₁₀H₆O₆S₂²⁻·C₃H₆N₆·5H₂O, are built up of neutral 2,4,6‐triamino‐1,3,5‐triazine (melamine), singly protonated melaminium cations, naphthalene‐1,5‐disulfonate dianions and water molecules. Two independent anions lie across centres of inversion in the space group P. The melamine molecules are connected by N—H...N hydrogen bonds into two different one‐dimensional polymers almost parallel to the (010) plane, forming a stacking structure along the b axis. The centrosymmetric naphthalene‐1,5‐disulfonate anions interact with water molecules via O—H...O hydrogen bonds, forming layers parallel to the (001) plane. The cations and anions are connected by N—H...O and O—H...N hydrogen bonds to form a three‐dimensional supramolecular framework.     

Hydrogen‐bonded supramolecular networks of N,N′‐bis(4‐pyridylmethyl)oxalamide and 4,4′‐{[oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate

The molecule of N,N′‐bis(4‐pyridylmethyl)oxalamide, C₁₄H₁₄N₄O₂, (I) or 4py‐ox, has an inversion center in the middle of the oxalamide group. Adjacent molecules are then linked through intermolecular N—H...N and C—H...O hydrogen bonds, forming an extended supramolecular network. 4,4′‐{[Oxalylbis(azanediyl)]dimethylene}dipyridinium dinitrate, C₁₄H₁₆N₄O₂²⁺·2NO₃⁻, (II), contains a diprotonated 4py‐ox cation and two nitrate counter‐anions. Each nitrate ion is hydrogen bonded to four 4py‐ox cations via intermolecular N—H...O and C—H...O interactions. Adjacent 4py‐ox cations are linked through weak C—H...O hydrogen bonding between an α‐pyridinium C atom and an oxalamide O atom, forming a two‐dimensional extended supramolecular network.     

A three‐dimensional supramolecular framework of silver(I), 2‐phenylquinoline‐4‐carboxylate and 4,4′‐bipyridine

A novel supramolecular framework, catena‐poly[[[aqua(2‐phenylquinoline‐4‐carboxylato‐κO)silver(I)]‐μ‐4,4′‐bipyridine‐κ²N:N′] dihydrate], {[Ag(C₁₆H₁₀NO₂)(C₁₀H₈N₂)(H₂O)]·2H₂O}_n, has been synthesized and structurally characterized. The Ag^I centres are four‐coordinated and bridged by 4,4′‐bipyridine (4,4′‐bipy) ligands to form a one‐dimensional Ag–bipy chain. The Ag–bipy chains are further linked together by intermolecular O—H...O and O—H...N hydrogen‐bonding interactions between adjacent chains, resulting in a three‐dimensional framework.     

N‐Cyclo­hexyl‐2‐[5‐(4‐pyridyl)‐4‐(p‐tolyl)‐4H‐1,2,4‐triazol‐3‐yl­sulfanyl]­acetamide dihydrate

In the title compound, C₂₂H₂₅N₅OS·2H₂O, the mol­ecules are stacked in columns running along the b axis. In this arrangemant, the mol­ecules are linked to each other by a combination of one two‐centre N—H⋯O hydrogen bond and four two‐centre O—H⋯O hydrogen bonds containing two types of ring motif, viz.R₄⁴(10) and R₃³(11). In the crystal structure, centrosymmetric π–π inter­actions between the triazole rings, with a distance of 3.691 (2) Å between the ring centroids, also affect the packing of the mol­ecules.     

2‐Ethyl‐6‐methylpyridin‐3‐ol and its salt bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate

The title compounds, C₈H₁₁NO, (I), and 2C₈H₁₂NO⁺·C₄H₄O₄²⁻, (II), both crystallize in the monoclinic space group P2₁/c. In the crystal structure of (I), intermolecular O—H...N hydrogen bonds combine the molecules into polymeric chains extending along the c axis. The chains are linked by C—H...π interactions between the methylene H atoms and the pyridine rings into polymeric layers parallel to the ac plane. In the crystal structure of (II), the succinate anion lies on an inversion centre. Its carboxylate groups interact with the 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium cations via intermolecular N—H...O hydrogen bonds with the pyridine ring H atoms and O—H...O hydrogen bonds with the hydroxy H atoms to form polymeric chains, which extend along the [01] direction and comprise R₄⁴(18) hydrogen‐bonded ring motifs. These chains are linked to form a three‐dimensional network through nonclassical C—H...O hydrogen bonds between the pyridine ring H atoms and the hydroxy‐group O atoms of neighbouring cations. π–π interactions between the pyridine rings and C—H...π interactions between the methylene H atoms of the succinate anion and the pyridine rings are also present in this network.     

Three‐dimensional networks in 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate

The two title proton‐transfer compounds, 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate, C₄H₇N₂⁺·C₇H₅O₆S⁻, (I), and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate, 2C₄H₇N₂⁺·C₇H₅O₆S²⁻, (II), are each organized into a three‐dimensional network by a combination of X—H...O (X = O, N or C) hydrogen bonds, and π–π and C—H...π interactions.     

The inner‐salt zwitterion,the dihydrochloride dihydrate and the dimethyl sulfoxide disolvate of 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid

In the inner‐salt zwitterion of 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid, (I), namely 5‐carboxy‐3‐(pyridin‐1‐ium‐2‐yl)‐6‐(pyridin‐2‐yl)pyrazine‐2‐carboxylate, [C₁₆H₁₀N₄O₄, (Ia)], the pyrazine ring has a twist–boat conformation. The opposing pyridine and pyridinium rings are almost perpendicular to one another, with a dihedral angle of 80.24 (18)°, and are inclined to the pyrazine mean plane by 36.83 (17) and 43.74 (17)°, respectively. The carboxy and carboxylate groups are inclined to the mean plane of the pyrazine ring by 43.60 (17) and 45.46 (17)°, respectively. In the crystal structure, the molecules are linked via N—H...O and O—H...O hydrogen bonds, leading to the formation of double‐stranded chains propagating in the [010] direction. On treating (Ia) with aqueous 1 M HCl, the diprotonated dihydrate form 2,2′‐(3,6‐dicarboxypyrazine‐2,5‐diyl)bis(pyridin‐1‐ium) dichloride dihydrate [C₁₆H₁₂N₄O₄²⁺·2Cl⁻·2H₂O, (Ib)] was obtained. The cation lies about an inversion centre. The pyridinium rings and carboxy groups are inclined to the planar pyrazine ring by 55.53 (9) and 19.8 (2)°, respectively. In the crystal structure, the molecules are involved in N—H...Cl, O—H...O_water and O_water—H...Cl hydrogen bonds, leading to the formation of chains propagating in the [010] direction. When (Ia) was recrystallized from dimethyl sulfoxide (DMSO), the DMSO disolvate 3,6‐bis(pyridin‐2‐yl)pyrazine‐2,5‐dicarboxylic acid dimethyl sulfoxide disolvate [C₁₆H₁₀N₄O₄·2C₂H₆OS, (Ic)] of (I) was obtained. Here, the molecule of (I) lies about an inversion centre and the pyridine rings are inclined to the planar pyrazine ring by only 23.59 (12)°. However, the carboxy groups are inclined to the pyrazine ring by 69.0 (3)°. In the crystal structure, the carboxy groups are linked to the DMSO molecules by O—H...O hydrogen bonds. In all three crystal structures, the presence of nonclassical hydrogen bonds gives rise to the formation of three‐dimensional supramolecular architectures.