dl‐Cysteinium semioxalate

Two chiral counterparts (l ‐ and d ‐cysteinium cations related by an inversion centre) are present in the structure of the title compound, C₃H₈NO₂S⁺·C₂HO₄⁻, with a 1:1 cation–anion ratio. The carboxy group of the cysteinium cation is protonated in the trans position relative to the amino group. The crystal structure is built up of double layers, in which dimers of cysteinium cations are connected to each other not directly, but via bridges of twisted semioxalate anions linked to each other via O—H...O hydrogen bonds forming infinite chains. An interesting feature of the crystal structure is the absence of either S—H...S or S—H...O hydrogen bonds.     

Bis(dl‐cysteinium) oxalate

In the title compound, 2C₃H₈NO₂S⁺·C₂O₄²⁻, the oxalate anion occupies an inversion centre and is coordinated to cysteine molecules of different chirality (l and d ) via O—H...O and N—H...O hydrogen bonds, the resulting cysteine–oxalate stoichiometry in the crystal structure being 2:1. The oxalate anion is completely deprotonated, whereas cysteine has a positively charged –NH₃⁺ group and a neutral protonated carboxyl group. The structure is built from infinite hydrogen‐bonded triple layers, consisting of an oxalate layer in the middle with layers of l ‐ and d ‐cysteine molecules on either side. The thiol groups are at the external sides of the layers and form S—H...O hydrogen bonds with the carboxyl groups of neighbouring cysteine molecules. An interesting feature of the structure is the occurrence of short S...S contacts between SH groups of molecules in neighbouring layers, which form not S—H...S but S—H...O intermolecular hydrogen bonds. Due to the effects of crystal packing and intermolecular hydrogen‐bond formation, the conformation of the cysteine cation in the title structure is different from that calculated theoretically for an individual cation, as well as from those of cysteine zwitterions in crystals of pure cysteine.     

l‐Cysteinium semioxalate: a new monoclinic polymorph or a hydrate?

The title compound, C₃H₈NO₂S⁺·C₂HO₄⁻, (I), crystallizes in the monoclinic C2 space group and is a new form (possibly a hydrate) of l ‐cysteinium semioxalate with a stoichiometric cation–anion ratio of 1:1. In contrast to the previously known orthorhombic form of l ‐cysteinium semioxalate, (I) has a layered structure resembling those of monoclinic l ‐cysteine, as well as of dl ‐cysteine and its oxalates. The conformations of the cysteinium cation and the oxalate anion in (I) differ substantially from those in the orthorhombic form. The structure of (I) has voids with a size sufficient to incorporate water molecules. The residual density, however, suggests that if water is in fact present in the voids, it is strongly disordered and its amount does not exceed 0.3 molecules per void. The difference in conformation of the cysteinium cations in (I) and in the orthorhombic form is similar to that in dl ‐cysteine under ambient conditions and in dl ‐cysteine under high pressure or at low temperature.     

Unusual hydrogen bonding in L‐cysteine hydrogen fluoride

L‐Cysteine hydrogen fluoride, or bis(L‐cysteinium) difluoride–L‐cysteine–hydrogen fluoride (1/1/1), 2C₃H₈NO₂S⁺·2F⁻·C₃H₇NO₂S·HF or L‐Cys⁺(L‐Cys...L‐Cys⁺)F⁻(F⁻...H—F), provides the first example of a structure with cations of the `triglycine sulfate' type, i.e.A⁺(A...A⁺) (where A and A⁺ are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter‐ion. The salt crystallizes in the monoclinic system with the space group P2₁. The dimeric (L‐Cys...L‐Cys⁺) cation and the dimeric (F⁻...H—F) anion are formed via strong O—H...O or F—H...F hydrogen bonds, respectively, with very short O...O [2.4438 (19) Å] and F...F distances [2.2676 (17) Å]. The F...F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O—H...F type, formed by a L‐cysteinium cation and a fluoride ion. The corresponding O...F distance of 2.3412 (19) Å seems to be the shortest among O—H...F and F—H...O hydrogen bonds known to date. The single‐crystal X‐ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above‐mentioned hydrogen bonds.     

The supramolecular architecture in 4,4′‐bipyridinium bis(hydrogen oxalate)

The asymmetric unit of the title compound, C₁₀H₁₀N₂²⁺·2C₂HO₄⁻, consists of one half of a 4,4′‐bipyridinium cation, which has inversion symmetry, and a hydrogen oxalate anion, in which an intramolecular hydrogen bond exists. The cations and anions are connected by O—H...O, N—H...O and C—H...O hydrogen bonds, forming a two‐dimensional network, whereas π–π stacking interactions involving the 4,4′‐bipyridinium cations lead to the formation of a three‐dimensional supramolecular structure. An unusual deca‐atomic ring is formed between two hydrogen oxalate anions, which are linked side‐to‐side via O—H...O hydrogen‐bonding interactions.     

4‐(3‐Azaniumylpropyl)morpholin‐4‐ium chloride hydrogen oxalate: an unusual example of a dication with different counter‐anions

The mixed organic–inorganic title salt, C₇H₁₈N₂O²⁺·C₂HO₄⁻·Cl⁻, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge‐assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dication, a hydrogen oxalate counter‐anion and an inorganic chloride counter‐anion. The organic cations and anions are connected through a network of N—H...O, O—H...O and C—H...O hydrogen bonds, forming several intermolecular rings that can be described by the graph‐set notations R₃³(13), R₂¹(5), R₁²(5), R₂¹(6), R₂³(6), R₂²(8) and R₃³(9). The 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dications are interconnected through N—H...O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O—H...O hydrogen bonds, forming head‐to‐tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N—H...O and O—H...O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4‐(3‐azaniumylpropyl)morpholin‐4‐ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three‐dimensional structure is stabilized via intermolecular N—H...Cl and C—H...Cl interactions.     

An optically resolved crystal of thiomalate: (S)‐1‐phenylethanaminium (R)‐thiomalate

The asymmetric unit of the optically resolved title salt, C₈H₁₂N⁺·C₄H₅O₄S⁻, contains a 1‐phenylethanaminium monocation and a thiomalate (3‐carboxy‐2‐sulfanylpropanoate) monoanion. The absolute configurations of the cation and the anion are determined to be S and R, respectively. In the crystal, cation–anion N—H...O hydrogen bonds, together with anion–anion O—H...O and S—H...O hydrogen bonds, construct a two‐dimensional supramolecular sheet parallel to the ab plane. The two‐dimensional sheet is linked with the upper and lower sheets through C—H...π interactions to stack along the c axis.     

Di­aza­bi­cyclo­[2.2.2]­octane‐1,4‐diium dichromate

The title compound, (C₆H₁₄N₂)[Cr₂O₇], consists of a di­aza­bi­cyclo­[2.2.2]­octane‐1,4‐diium cation and a discrete dichromate anion, which are linked in the crystal by N—H⋯O hydrogen bonds. The cation is ordered and distorted, owing to the confinement and twist of the hydrogen bonds involved. Two CrO₄ tetrahedra are joined through a shared O atom to form the dichromate anion. Chiral supramolecular chains of the title compound are built up via N—H⋯O hydrogen bonds, and C—H⋯O interactions play subordinate roles in forming the structure.     

dl‐Alaninium semi‐oxalate monohydrate

The structure of the title compound, C₃H₈NO₂⁺·C₂HO₄⁻·H₂O, is formed by two chiral counterparts (l ‐ and d ‐alaninium cations), semi‐oxalate anions and water molecules, with a 1:1:1 cation–anion–water ratio. The structure is compared with that of the previously known anhydrous dl ‐alaninium semi‐oxalate [Subha Nandhini, Krishnakumar & Natarajan (2001). Acta Cryst. E 57 , o666–o668] in order to investigate the role of water molecules in the crystal packing. The structure of the hydrate resembles that of anhydrous alaninium semi‐oxalate, with the water molecule incorporated into the general three‐dimensional network of hydrogen bonds where it forms four hydrogen bonds with neighbours disposed tetrahedrally about it. Although the main structural motifs in the hydrate and in the anhydrous form are topologically similar, the incorporation of water molecules in the network results in significant geometric distortion. There are several types of hydrogen bond in the crystal structure of the hydrate, two of which (O—H...O bonds between the semi‐oxalate anions and O—H...O hydrogen bonds between water and alaninium cations) are very short. Such hydrogen bonds between semi‐oxalate anions are also present in the anhydrous form of this compound. Short distances between semi‐oxalate anions in neighbouring chains in the hydrate alternate with longer ones, whereas in the anhydrous structure they are equidistant. Despite the similarity of these compounds, dehydration of the hydrate on storage is not of a single‐crystal to single‐crystal type, but gives a polycrystalline pseudomorph, preserving the crystal habit. This transformation proceeds through the formation of an intermediate compound, presumably a hemihydrate.     

(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.     

Aripiprazole salts. III. Bis(aripiprazolium) oxalate–oxalic acid (1/1)

The asymmetric unit of the title salt [systematic name: bis(4‐(2,3‐dichlorophenyl)‐1‐{4‐[(2‐oxo‐1,2,3,4‐tetrahydroquinolin‐7‐yl)oxy]butyl}piperazin‐1‐ium) oxalate–oxalic acid (1/1)], 2C₂₃H₂₈Cl₂N₃O₂⁺·C₂O₄²⁻·C₂H₂O₄, consists of one protonated aripiprazole unit (HArip⁺), half an oxalate dianion and half an oxalic acid molecule, the latter two lying on inversion centres. The conformation of the HArip⁺ cation differs from that in other reported salts and resembles more the conformation of neutral Arip units in reported polymorphs and solvates. The intermolecular interaction linking HArip⁺ cations is also similar to those in reported Arip compounds crystallizing in the space group P, with head‐to‐head N—H...O hydrogen bonds generating centrosymmetric dimers, which are further organized into planar ribbons parallel to (01). The oxalate anions and oxalic acid molecules form hydrogen‐bonded chains running along [010], which `pierce' the planar ribbons, interacting with them through a number of stronger N—H...O and weaker C—H...O hydrogen bonds, forming a three‐dimensional network.     

Bis(dihydronium) naphthalene‐1,5‐disulfonate

The title compound is a salt, 2H₅O₂⁺·C₁₀H₆O₆S₂²⁻, in which the anion lies across an inversion centre in the space group C2/c, while the cation contains a short but noncentred O—H...O hydrogen bond. The ionic components are linked by charge‐assisted O—H...O hydrogen bonds into a three‐dimensional framework structure.     

Bis(glycinium) oxalate: evidence of strong hydrogen bonding

In the title 2:1 salt, 2C₂H₆NO₂⁺·C₂O₄²⁻, the glycine mol­ecule is in the cationic form with a positively charged amino group and an uncharged carboxylic acid group. The doubly charged oxalate anion lies across a crystallographic inversion centre. One of the reasons why the 1:1 glycinium oxalate salt has a higher melting point than the title compound may be the difference in their hydrogen‐bonding patterns. A database search for salts formed between amino acids or substituted amino acids and oxalic acid revealed that, in most of the structures, the conformation about the O=C—OH bond is synplanar. d ‐Tryptophan oxalate is the only example where the OH group of a semi‐oxalate adopts an anti­planar conformation. The 2:1 stoichiometry seen in the present salt is observed only in the salts of dl ‐serine, dl ‐aspartic acid and betaine with oxalic acid.     

3‐[(Diphenylphosphinothioyl)oxy]‐N‐methylpropan‐1‐aminium diphenylphosphanylthioate

The title salt, C₁₆H₂₁NOPS⁺·C₁₂H₁₀OPS, was synthesized from the reaction between 3‐(methylamino)propan‐1‐ol and PPh₂(S)Cl in the presence of Et₃N. Its structure has been identified using spectroscopic methods and X‐ray analysis. Single crystals were obtained from ethanol by slow evaporation. In the asymmetric unit, a cation–anion pair is formed through an intermolecular N—H...O [N...O = 2.6974 (18) Å] hydrogen bond. The molecules are packed through N—H...O and N—H...S hydrogen bonds in the crystal and these hydrogen bonds are responsible for the high melting point. The P atoms of the anion and cation both have distorted tetrahedral environments.     

Phenyl‐ring rotational disorder in the two‐dimensional hydrogen‐bonded structure of the 1:1 proton‐transfer salt of the diazo‐dye precursor 4‐(phenyldiazenyl)aniline (aniline yellow) with l‐tartaric acid

In the structure of the 1:1 proton‐transfer compound from the reaction of l ‐tartaric acid with the azo‐dye precursor aniline yellow [4‐(phenyldiazenyl)aniline], namely 4‐(phenyldiazenyl)anilinium (2R,3R)‐3‐carboxy‐2,3‐dihydroxypropanoate, C₁₂H₁₂N₃⁺·C₄H₅O₆⁻, the asymmetric unit contains two independent 4‐(phenyldiazenyl)anilinium cations and two hydrogen l ‐tartrate anions. The structure is unusual in that all four phenyl rings of the two cations have identical rotational disorder with equal occupancy of the conformations. The two hydrogen l ‐tartrate anions form independent but similar chains through head‐to‐tail carboxyl–carboxylate O—H...O hydrogen bonds [graph set C(7)], which are then extended into a two‐dimensional hydrogen‐bonded sheet structure through hydroxy O—H...O hydrogen‐bonded links. The anilinium groups of the 4‐(phenyldiazenyl)anilinium cations are incorporated into the sheets and also provide internal hydrogen‐bonded extensions, while their aromatic tails are layered in the structure without significant association except for weak π–π interactions [minimum ring centroid separation = 3.844 (3) Å]. The hydrogen l ‐tartrate residues of both anions exhibit the common short intramolecular hydroxy–carboxylate O—H...O hydogen bonds. This work provides a solution to the unusual disorder problem inherent in the structure of this salt, as well as giving another example of the utility of the hydrogen tartrate anion in the generation of sheet substructures in molecular assembly processes.     

Tetra­phenyl­phos­phonium 4‐hydroxy‐2,2,6,6‐tetra­methyl­piperidinyl­oxy‐4‐sulfonate

The title compound, C₂₄H₂₀P⁺·C₉H₁₇NO₅S⁻, consists of an organic monovalent cation and an organic monovalent anion, the latter being derived from the TEMPO radical (TEMPO is 2,2,6,6‐tetra­methyl­piperidin‐1‐oxyl). Two inversion‐related anions interact via two –O—H⃛O—S– hydrogen bonds, forming a dimer in which there are no short contacts between the spin centres (–N—O) of the TEMPO(OH)SO₃⁻ anions. Furthermore, no significant magnetic interaction is observed between the dimers because the dimer is surrounded by cations. These results are consistent with the paramagnetic behaviour of the title salt.     

Dicyclohexylammonium bromoacetate: a low molecular mass organogelator with a one‐dimensional secondary ammonium monocarboxylate (SAM) synthon

The asymmetric unit of the title salt, C₁₂H₂₄N⁺·C₂H₂BrO₂⁻, contains a dicyclohexylammonium cation connected to a bromoacetate anion by means of an N—H...O hydrogen bond. In the crystal, the ion pairs assemble via N—H...O interactions, forming zigzag infinite chains parallel to the c axis with the (...H—N—H...O—C—O...)_n motif that is considered to be a prerequisite for ensuring gelation properties of secondary ammonium monocarboxylate salts. The title salt was characterized by FT–IR, X‐ray powder diffraction (XRPD), TG–DTA and ¹H NMR spectroscopy in solution. Gelation experiments revealed that dicyclohexylammonium bromoacetate forms molecular gels with dimethylformamide and dimethyl sulfoxide. Scanning electron microscopy (SEM) was used to reveal morphological features of dried gels.     

N‐Acetyl‐l‐tyrosine methyl ester monohydrate at 293 and 123 K

The crystal structure of a protected l ‐tyrosine, namely N‐acetyl‐l ‐tyrosine methyl ester monohydrate, C₁₂H₁₅NO₄·H₂O, was determined at both 293 (2) and 123 (2) K. The structure exhibits a network of O—H...O and N—H...O hydrogen bonds, in which the water molecule plays a crucial role as an acceptor of one and a donor of two hydrogen bonds. Molecules of water and of the protected l ‐tyrosine form hydrogen‐bonded layers perpendicular to [001]. C—H...π interactions are observed in the hydrophobic regions of the structure. The structure is similar to that of N‐acetyl‐l ‐tyrosine ethyl ester monohydrate [Soriano‐García (1993). Acta Cryst. C 49 , 96–97].     

Hydrogen‐bonding motifs in 3‐carboxyanilinium bromide and iodide

In the title compounds, C₇H₈NO₂⁺·Br⁻, (I), and C₇H₈NO₂⁺·I⁻, (II), the asymmetric unit contains a discrete 3‐carboxyanilinium cation, with a protonated amine group, and a halide anion. The compounds are not isostructural, and the crystal structures of (I) and (II) are characterized by different two‐dimensional hydrogen‐bonded networks. The ions in (I) are connected into ladder‐like ribbons via N—H...Br hydrogen bonds, while classic cyclic O—H...O hydrogen bonds between adjacent carboxylic acid functions link adjacent ribbons to give three characteristic graph‐set motifs, viz. C₂¹(4), R₄²(8) and R₂²(8). The ions in (II) are connected via N—H...I, N—H...O and O—H...I hydrogen bonds, also with three characteristic graph‐set motifs, viz. C(7), C₂¹(4) and R₄²(18), but an O—H...O interaction is not present.     

Two new structures in the glycine–oxalic acid system

Glycinium semi‐oxalate‐II, C₂H₆NO₂⁺·C₂HO₄⁻, (A), and diglycinium oxalate methanol disolvate, 2C₂H₆NO₂⁺·C₂O₄²⁻·2CH₃OH, (B), are new examples in the glycine–oxalic acid family. (A) is a new polymorph of the known glycinium semi‐oxalate salt, (C). Compounds (A) and (C) have a similar packing of the semi‐oxalate monoanions with respect to the glycinium cations, but in (A) the two glycinium cations and the two semi‐oxalate anions in the asymmetric unit are non‐equivalent, and the binding of the glycinium cations to each other is radically different. Based on this difference, one can expect that, although the two forms grow concomitantly from the same batch, a transformation between (A) and (C) in the solid state should be difficult. In (B), two glycinium cations and an oxalate anion, which sits across a centre of inversion, are linked via strong short O—H...O hydrogen bonds to form the main structural fragment, similar to that in diglycinium oxalate, (D). Methanol solvent molecules are embedded between the glycinium cations of neighbouring fragments. These fragments form a three‐dimensional network via N—H...O hydrogen bonds. Salts (B) and (D) can be obtained from the same solution by, respectively, slow or rapid antisolvent crystallization.