9α‐Fluoro‐16α‐methyl‐3,11‐dioxoandrosta‐1,4‐diene‐17β‐carboxyl­ic acid: catemeric hydrogen bonding and acetic acid solvation in a steroidal keto acid related to dexamethasone

The title keto acid crystallizes as a solvate, C₂₁H₂₅FO₄·C₂H₄O₂, with two mol­ecules each of steroid and acetic acid per asymmetric unit. The former are approximately parallel, with opposite end‐to‐end orientation, and form translational carboxyl‐to‐ketone hydrogen‐bonding catemers [O⋯O = 2.679 (6) and 2.650 (5) Å, and O—H⋯O = 165 and 162°] that involve the 3‐ketone group and follow the a axis. The acetic acid mol­ecules are paired by hydrogen bonding, and neither they nor the F atom nor the 11‐ketone group play any overt role in the hydrogen‐bonding scheme of the steroid. Intermolecular C—H⋯O=C close contacts involving three different neighboring mol­ecules exist to the 11‐ketone group, the steroidal carboxyl group and one of the acetic acid molecules.     

Three‐dimensional hydrogen‐bonded structures in the 1:1 proton‐transfer compounds of l‐tartaric acid with the associative‐group monosubstituted pyridines 3‐aminopyridine, 3‐carboxypyridine (nicotinic acid) and 2‐carboxypyridine (picolinic acid)

The 1:1 proton‐transfer compounds of l ‐tartaric acid with 3‐aminopyridine [3‐aminopyridinium hydrogen (2R,3R)‐tartrate dihydrate, C₅H₇N₂⁺·C₄H₅O₆⁻·2H₂O, (I)], pyridine‐3‐carboxylic acid (nicotinic acid) [anhydrous 3‐carboxypyridinium hydrogen (2R,3R)‐tartrate, C₆H₆NO₂⁺·C₄H₅O₆⁻, (II)] and pyridine‐2‐carboxylic acid [2‐carboxypyridinium hydrogen (2R,3R)‐tartrate monohydrate, C₆H₆NO₂⁺·C₄H₅O₆⁻·H₂O, (III)] have been determined. In (I) and (II), there is a direct pyridinium–carboxyl N⁺—H...O hydrogen‐bonding interaction, four‐centred in (II), giving conjoint cyclic R₁²(5) associations. In contrast, the N—H...O association in (III) is with a water O‐atom acceptor, which provides links to separate tartrate anions through O_hydroxy acceptors. All three compounds have the head‐to‐tail C(7) hydrogen‐bonded chain substructures commonly associated with 1:1 proton‐transfer hydrogen tartrate salts. These chains are extended into two‐dimensional sheets which, in hydrates (I) and (III) additionally involve the solvent water molecules. Three‐dimensional hydrogen‐bonded structures are generated via crosslinking through the associative functional groups of the substituted pyridinium cations. In the sheet struture of (I), both water molecules act as donors and acceptors in interactions with separate carboxyl and hydroxy O‐atom acceptors of the primary tartrate chains, closing conjoint cyclic R₄⁴(8), R₃⁴(11) and R₃³(12) associations. Also, in (II) and (III) there are strong cation carboxyl–carboxyl O—H...O hydrogen bonds [O...O = 2.5387 (17) Å in (II) and 2.441 (3) Å in (III)], which in (II) form part of a cyclic R₂²(6) inter‐sheet association. This series of heteroaromatic Lewis base–hydrogen l ‐tartrate salts provides further examples of molecular assembly facilitated by the presence of the classical two‐dimensional hydrogen‐bonded hydrogen tartrate or hydrogen tartrate–water sheet substructures which are expanded into three‐dimensional frameworks via peripheral cation bifunctional substituent‐group crosslinking interactions.     

(+)‐Camphor­acetic acid: catemeric hydrogen bonding in a γ‐keto acid

The title compound, (1R)‐4,7,7‐tri­methyl‐3‐oxobi­cyclo­[2.2.1]­heptane‐2‐endo‐acetic acid, C₁₂H₁₈O₃, like its lower homolog, forms carboxyl‐to‐ketone hydrogen‐bonding catemers (Z′ = 2) [O⋯O = 2.729 (5) and 2.707 (5) Å, and O—H⋯O = 165 and 170°] with screw‐related components. The two mol­ecules of the asymmetric unit differ slightly in conformation and produce two counter‐aligned hydrogen‐bonding chains, both aligned with the b axis. Close intermolecular C—H⋯O=C contacts exist for the ketone group of one mol­ecule and for both the ketone and carboxyl functions in the other.     

(–)‐2‐(1,2,3,4,4a,5,6,7,8,8aα‐Decahydro‐4aβ,8α‐dimethyl‐7‐oxo‐2β‐naphthyl)propionic acid: catemeric hydrogen bonding in a bicyclic sesquiterpenoid ζ‐keto acid

In the title compound, C₁₅H₂₄O₃, derived from a naturally occurring sesquiterpenoid, the asymmetric unit consists of two mol­ecules differing by 167.4 (8)° in the rotational conformation of the carboxyl group. Each molecule aggregates separately with its own type as carboxyl‐to‐ketone hydrogen‐bonding catemers [O⋯O = 2.715 (6) and 2.772 (6) Å, and O—H⋯O = 169 and 168°]. This generates two crystallographically independent single‐strand hydrogen‐bonding helices passing through the cell in the b direction, with opposite end‐to‐end orientations. One intermolecular C—H⋯O=C close contact exists for the carboxyl group of one of the mol­ecules. The structure is isostructural with that of a closely related unsaturated keto acid reported previously.     

2‐Pyridone–tartronic acid (1/1), 3‐hydroxy­pyridinium hydrogen tartronate and 4‐hydroxy­pyridinium hydrogen tartronate

Tartronic acid forms a hydrogen‐bonded complex, C₅H₅NO·C₃H₄O₅, (I), with 2‐pyridone, while it forms acid salts, namely 3‐hydroxy­pyridinium hydrogen tartronate, (II), and 4‐hy­droxy­pyridinium hydrogen tartronate, (III), both C₅H₆NO⁺·C₃H₃O₅⁻, with 3‐hydroxy­pyridine and 4‐hydroxy­pyridine, respectively. In (I), the pyridone mol­ecules and the acid mol­ecules form R(8) and R(10) hydrogen‐bonded rings, respectively, around the inversion centres. In (II) and (III), the cations and anions are linked by N—H⋯O and O—H⋯O hydrogen bonds to form a hydrogen‐bonded chain. In each of (I), (II) and (III), an intermolecular hydrogen bond is formed between a carboxyl group and the hydroxyl group attached to the central C atom, and in (I), the hydroxyl group participates in an intramolecular hydrogen bond with a carbonyl group. No intermolecular hydrogen bond is formed between the carboxyl groups in (I), or between the carboxyl and carboxyl­ate groups in (II) and (III).     

(–)‐Gibberic acid: hydrogen‐bonding pattern of the monohydrate of a non‐­racemic tetracyclic δ‐keto acid derivative of gibberellin A3

In the the title compound, 1,7‐di­methyl‐8‐oxo‐4bα,7α‐gibba‐1,3,4a(10a)‐triene‐10β‐carboxyl­ic acid monohydrate, C₁₈H₂₀O₃·H₂O, the water of hydration accepts a hydrogen bond from the carboxyl and donates hydrogen bonds to the carboxyl carbonyl and the ketone in two different screw‐related neighbors, which are mutually translational, yielding a complex three‐dimensional hydrogen‐bonding array.     

Poly[triaqua(μ4‐4‐carboxybenzenesulfonato‐κ4O:O′:O′′:O′′′)(4‐carboxybenzenesulfonato‐κO)strontium(II)]

This study presents the coordination modes and two‐dimensional network of a novel strontium(II) coordination polymer, [Sr(C₇H₅O₅S)₂(H₂O)₃]_n. The eight‐coordinate Sr²⁺ ion is in a distorted bis‐disphenoidal coordination environment, surrounded by four sulfonate and one carboxyl O atom from five benzenesulfonate ligands, two of which are symmetry unique, and by three O atoms from three independent aqua ligands. The compound exhibits a monolayer structure with coordination bonds within and hydrogen bonds between the layers. The μ₄ acid ligand bridges the metal ions in two dimensions to form a thick undulating monolayer with a hydrophobic interior and hydrophilic surfaces. A second independent monoanion is arranged outward from both sides of the monolayer and serves to link adjacent monolayers via carboxyl–water and water–carboxyl 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.     

Supramolecular architectures in the salt trimethoprimium ferrocene‐1‐carboxylate and the cocrystal 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–ferrocene‐1‐carboxylic acid (1/1)

In the salt trimethoprimium ferrocenecarboxylate [systematic name: 2,4‐diamino‐5‐(3,4,5‐trimethoxybenzyl)pyrimidin‐1‐ium ferrocene‐1‐carboxylate], (C₁₄H₁₉N₄O₃)[Fe(C₅H₅)(C₆H₄O₂)], (I), of the antibacterial compound trimethoprim, the carboxylate group interacts with the protonated aminopyrimidine group of trimethoprim via two N—H…O hydrogen bonds, generating a robust R ₂²(8) ring motif (heterosynthon). However, in the cocrystal 4‐amino‐5‐chloro‐2,6‐dimethylpyrimidine–ferrocene‐1‐carboxylic acid (1/1), [Fe(C₅H₅)(C₆H₅O₂)]·C₆H₈ClN₃, (II), the carboxyl–aminopyrimidine interaction [R ₂²(8) motif] is absent. The carboxyl group interacts with the pyrimidine ring via a single O—H…N hydrogen bond. The pyrimidine rings, however, form base pairs via a pair of N—H…N hydrogen bonds, generating an R ₂²(8) supramolecular homosynthon. In salt (I), the unsubstituted cyclopentadienyl ring is disordered over two positions, with a refined site‐occupation ratio of 0.573 (10):0.427 (10). In this study, the two five‐membered cyclopentadienyl (Cp) rings of ferrocene are in a staggered conformation, as is evident from the C…Cg …Cg …C pseudo‐torsion angles, which are in the range 36.13–37.53° for (I) and 22.58–23.46° for (II). Regarding the Cp ring of the minor component in salt (I), the geometry of the ferrocene ring is in an eclipsed conformation, as is evident from the C…Cg …Cg …C pseudo‐torsion angles, which are in the range 79.26–80.94°. Both crystal structures are further stabilized by weak π–π interactions.     

(2S)‐1‐Carbamoylpyrrolidine‐2‐carboxylic acid

In the title compound, also known as N‐carbamoyl‐l ‐proline, C₆H₁₀N₂O₃, the pyrrolidine ring adopts a half‐chair conformation, whereas the carboxyl group and the mean plane of the ureide group form an angle of 80.1 (2)°. Molecules are joined by N—H...O and O—H...O hydrogen bonds into cyclic structures with graph‐set R²₂(8), forming chains in the b‐axis direction that are further connected via N—H...O hydrogen bonds into a three‐dimensional network.     

Crystallographic characterization of the first reported crystalline form of the potent hallucinogen (R)‐2‐amino‐1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propane or `bromodragonfly': the 1:1 anhydrous proton‐transfer compound with 3,5‐dinitrosalicylic acid

The 1:1 proton‐transfer compound of the potent substituted amphetamine hallucinogen (R)‐2‐amino‐1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propane (common trivial name `bromodragonfly') with 3,5‐dinitrosalicylic acid, namely 1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propan‐2‐aminium 2‐carboxy‐4,6‐dinitrophenolate, C₁₃H₁₃BrNO₂⁺·C₇H₃N₂O₇⁻, forms hydrogen‐bonded cation–anion chain substructures comprising undulating head‐to‐tail anion chains formed through C(8) carboxyl–nitro O—H...O associations and incorporating the aminium groups of the cations. The intrachain cation–anion hydrogen‐bonding associations feature proximal cyclic R₃³(8) interactions involving both an N⁺—H...O_phenolate and the carboxyl–nitro O—H...O associations and aromatic π–π ring interactions [minimum ring centroid separation = 3.566 (2) Å]. A lateral hydrogen‐bonding interaction between the third aminium H atom and a carboxyl O‐atom acceptor links the chain substructures, giving a two‐dimensional sheet structure. This determination represents the first of any form of this compound and is in the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen‐bonded chain substructures provided by the anions, which accommodate the aminium proton‐donor groups of the cations and give crosslinking, and to the presence of the cation–anion aromatic ring π–π interactions.     

Hydrogen‐bonded 1:1 adduct of 1,1′‐(p‐phenylene)dipyridin‐4(1H)‐one with terephthalic acid

Cocrystallization of 1,1′‐(p‐phenylene)dipyridin‐4(1H)‐one (4,4′‐dpy) and terephthalic acid (tpa) affords the hydrogen‐bonded 1:1 title complex, C₁₆H₁₂N₂O₂·C₈H₆O₄. Both mol­ecules are symmetrically disposed about independent symmetry centers. Strong O—H⋯O hydrogen bonds between tpa carboxyl groups and 4,4′‐dpy carbonyl groups produce one‐dimensional zigzag infinite chains. Each chain is linked to four surrounding chains via weak C—H⋯O inter­actions, resulting in a three‐dimensional mol­ecular framework.     

4‐Carboxyanilinium (2R,3R)‐tartrate and a redetermination of the α‐polymorph of 4‐aminobenzoic acid

In the title compounds, 4‐carboxyanilinium (2R,3R)‐tartrate, C₇H₈NO₂⁺·C₄H₅O₆⁻, (I), and 4‐aminobenzoic acid, C₇H₇NO₂, (II), the carboxyl planes of the 4‐carboxyanilinium cations/4‐aminobenzoic acid are twisted from the aromatic plane. In (I), the characteristic head‐to‐tail interactions are observed through the tartrate anions, forming two C₂²(7) chain motifs propagating parallel to the a and c axes of the unit cell. Also, the tartrate anions are connected through two primary C₁¹(6) and C₁¹(7) chain motifs, leading to a secondary R₄⁴(22) ring motif. In (II), head‐to‐tail interaction is seen through a discrete D₁¹(2) motif and carboxyl group dimerization is observed through centrosymmetrically related R₂²(8) motifs around the inversion centres of the unit cell. The crystal structures of both compounds are stabilized by intricate three‐dimensional hydrogen‐bonding networks. Alternate hydrophobic and hydrophilic layers are observed in (I) as a result of a column‐like arrangement of the anions and the aromatic rings of the cations.     

(E)‐2‐Methyl‐5‐(1‐naphthyl­methyl)­cinnamic acid

The title compound, C₂₁H₁₈O₂, crystallized in the centrosymmetric space group P2₁/n with one mol­ecule in the asymmetric unit. There is a single hydrogen bond, with an O_donor?O_acceptor distance of 2.624 (2) Å, which forms a cyclic dimer about a center of symmetry. The carboxyl group O atoms are ordered, while the carboxyl‐H atom is disordered. A single leading intermolecular C—H?O interaction has an H?O distance of 2.68 Å and a C—H?O angle of 178°; this interaction forms chains. Taken together with the hydrogen bond, it generates chains and rings. Structural comparisons are made with trans‐cinnamic acid and with 4‐methyl‐trans‐cinnamic acid.     

catena‐Poly[[[cis‐aqua­bis(4‐carboxy­cyclo­hexane‐1‐carboxyl­ato‐κ2O,O′)cadmium(II)]‐μ‐4,4′‐bipyridine‐κ2N:N] monohydrate]

The title complex, {[Cd(C₈H₁₁O₄)₂(C₁₀H₈N₂)(H₂O)]·H₂O}_n, consists of linear chains formed through 4,4′‐bipyridine ligands linking seven‐coordinated Cd^II ions. Each Cd^II ion is in a distorted penta­gonal–bipyramidal environment, coordinated by one water ligand, two 4‐carboxy­cyclo­hexane‐1‐carboxyl­ate ligands and one bridging 4,4′‐bipyridine ligand to generate linear chains. The water mol­ecules and the Cd atom on one side, and the 4,4′‐bipyridine unit on the other, are bisected by two sets of twofold axes. The carboxylate group of the 4‐carboxy­cyclo­hexane‐1‐carboxyl ligand chelates a Cd^II ion, while the (protonated) carboxyl group forms hydrogen bonds with adjacent chains, resulting in a layered structure. This is the first reported occurrence of a dicarboxycyclo­hexane ligand exhibiting a non‐bridging coordination mode.     

(−)‐3,6‐Dioxo‐5β‐cholanic acid: hydrogen bonding in the hemihydrate of a steroidal diketo acid

The hemihydrate of the title diketo acid, C₂₄H₃₆O₄·0.5H₂O, forms hydrogen‐bonded carboxyl dimers related by a C₂ axis at crystallographic sites on the a and b edges of the chosen cell [O?O = 2.643 (7) and 2.716 (7) Å]. The ketone ends of the mol­ecules approach each other at sites near (½,½,½), (½,0,½), (0,0,½) and (0,½,½) in an interleaved arrangement incorporating partial‐occupancy water hydrogen bonded to the B‐ring ketone.     

Hydrogen bonding and π–π interactions in 1‐benzofuran‐2,3‐dicarboxylic acid and its 1:1 cocrystals with pyridine,phenazine and 1,4‐phenylenediamine

The structure of 1‐benzofuran‐2,3‐dicarboxylic acid (BFDC), C₁₀H₆O₅, (I), exhibits an intramolecular hydrogen bond between one –COOH group and the other, while the second carboxyl function is involved in intermolecular hydrogen bonding to neighbouring species. The latter results in the formation of flat one‐dimensional hydrogen‐bonded chains in the crystal structure, which are π–π stacked along the normal to the plane of the molecular framework, forming a layered structure. 1:1 Cocrystallization of BFDC with pyridine, phenazine and 1,4‐phenylenediamine is associated with H‐atom transfer from BFDC to the base and charge‐assisted hydrogen bonding between the BFDC⁻ monoanion and the corresponding ammonium species, while preserving, in all cases, the intramolecular hydrogen bond between the carboxyl and carboxylate functions. The pyridinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C₅H₆N⁺·C₁₀H₅O₅⁻, (II), and phenazinium 3‐carboxylato‐1‐benzofuran‐2‐carboxylic acid, C₁₂H₉N₂⁺·C₁₀H₅O₅⁻, (III), adducts form discrete hydrogen‐bonded ion‐pair entities. In the corresponding crystal structures, the two components are arranged in either segregated or mixed π–π stacks, respectively. On the other hand, the structure of 4‐aminoanilinium 2‐carboxylato‐1‐benzofuran‐3‐carboxylic acid, C₆H₉N₂⁺·C₁₀H₅O₅⁻, (IV), exhibits an intermolecular hydrogen‐bonding network with three‐dimensional connectivity. Moreover, this fourth structure exhibits induction of supramolecular chirality by the extended hydrogen bonding, leading to a helical arrangement of the interacting moieties around 2₁ screw axes. The significance of this study is that it presents the first crystallographic characterization of pure BFDC, and manifestation of its cocrystallization with a variety of weakly basic amine molecules. It confirms the tendency of BFDC to preserve its intramolecular hydrogen bond and to prefer a monoanionic form in supramolecular association with other components. The aromaticity of the flat benzofuran residue plays an important role in directing either homo‐ or heteromolecular π–π stacking in the first three structures, while the occurrence of a chiral architecture directed by multiple hydrogen bonding is the dominant feature in the fourth.     

7‐Oxobi­cyclo­[2.2.1]­heptane‐1‐carboxylic acid and ()‐7‐oxobi­cyclo­[2.2.1]­hept‐5‐ene‐2‐endo‐carboxylic acid: hydrogen bonding in two norbornyl keto acids

Molecules of the title β‐keto acid, 7‐oxobi­cyclo­[2.2.1]­heptane‐1‐carboxylic acid, C₈H₁₀O₃, exhibit chirality due to the bridgehead carboxyl group, which is partially ordered and has a slightly asymmetric conformation. The mol­ecules form centrosymmetric hydrogen‐bonded carboxyl dimers [O?O 2.639 (2) Å]. The title alkenoic γ‐keto acid, ()‐7‐oxobi­cyclo­[2.2.1]­hept‐5‐ene‐2‐endo‐carboxylic acid, C₈H₈O₃, also forms typical centrosymmetric hydrogen‐bonded carboxyl dimers [O?O 2.660 (3) Å]. There is partial disorder of the carboxyl group in each compound.     

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.