Two polymorphs of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate

Crystallization (from ethyl acetate solution) of 2‐(4‐chlorophenyl)‐4‐methylchromenium perchlorate, C₁₆H₁₂ClO⁺·;ClO₄⁻, (I), yields two monoclinic polymorphs with the space groups P2₁/n [polymorph (Ia)] and P2₁/c [polymorph (Ib)]; in both cases, Z = 4. Cations and anions, disordered in polymorph (Ib), form ion pairs in both polymorphs as a result of Cl—O...π interactions. Related by a centre of symmetry, neighbouring ion pairs in polymorph (Ia) are linked viaπ–π interactions between cationic fragments, and the resulting dimers are linked through a network of C—H...O(perchlorate) interactions between adjacent cations and anions. The ion pairs in polymorph (Ib), arranged in pairs of columns along the a axis, are linked through a network of C—H...O(perchlorate), C—Cl...π, π–π and C—Cl...O(perchlorate) interactions. The aromatic skeletons in polymorph (Ia) are parallel in the cationic fragments involved in dimers, but nonparallel in adjacent ion pairs not constituting dimers. In polymorph (Ib), these skeletons are parallel in pairs of columns, but nonparallel in adjacent pairs of columns; this is visible as a herring‐bone pattern. Differences in the crystal structures of the polymorphs are most probably the cause of their different colours.     

Two tautomeric polymorphs of 2,6‐dichloropurine

Two polymorphs of 2,6‐dichloropurine, C₅H₂Cl₂N₄, have been crystallized and identified as the 9H‐ and 7H‐tautomers. Despite differences in the space group and number of symmetry‐independent molecules, they exhibit similar hydrogen‐bonding motifs. Both crystal structures are stabilized by intermolecular N—H...N interactions that link adjacent molecules into linear chains, and by some nonbonding contacts of the C—Cl...π type and by π–π stacking interactions, giving rise to a crossed two‐dimensional herringbone packing motif. The main structural difference between the two polymorphs is the different role of the molecules in the π–π stacking interactions.     

Two polymorphs of anhydrous 4‐pyridone at 100 K

Two polymorphs of the title compound, C₅H₅NO, (I), have been obtained from ethanol. One polymorph crystallizes in the monoclinic space group C2/c [henceforth (I)‐M], while the other crystallizes in the orthorhombic space group Pbca [henceforth (I)‐O]. In the two forms, the lattice parameters, cell volume and packing motifs are very similar. There are also two independent molecules of 4‐pyridone in each asymmetric unit. The molecules are linked by N—H...O hydrogen bonds into one‐dimensional zigzag chains extending along the b axis in the (I)‐M polymorph and along the a axis in the (I)‐O polymorph, with the graph set C₂²(12). The structures are stabilized by weak C—H...O hydrogen bonds linking adjacent chains, thus forming a ring with the graph set R₆⁵(28). The significance of this study lies in the analysis of the hydrogen‐bond interactions occurring in these structures. Analyses of the crystal structures of the two polymorphs of 4‐pyridone are helpful in elucidating the mechanism of the generation of spectroscopic effects observed in the IR spectra of these polymorphs in the frequency range of the N—H stretching vibration band.     

l‐Cysteinium semioxalate

The title salt, C₃H₈NO₂⁺·C₂HO₄⁻, formed between l ‐cysteine and oxalic acid, was studied as part of a comparison of the structures and properties of pure amino acids and their cocrystals. The structure of the title salt is very different from that formed by oxalic acid and equivalent amounts of d ‐ and l ‐cysteine molecules. The asymmetric unit contains an l ‐cysteinium cation and a semioxalate anion. The oxalate anion is only singly deprotonated, in contrast with the double deprotonation in the crystal structure of bis(dl ‐cysteinium) oxalate. The oxalate anion is not planar. The conformation of the l ‐cysteinium cation differs from that of the neutral cysteine zwitterion in the monoclinic and orthorhombic polymorphs of l ‐cysteine, but is similar to that of the cysteinium cation in bis(dl ‐cysteinium) oxalate. The structure of the title salt can be described as a three‐dimensional framework formed by ions linked by strong O—H...O and N—H...O and weak S—H...O hydrogen bonds, with channels running along the crystallographic a axis containing the bulky –CH₂SH side chains of the cysteinium cations. The cations are only linked through hydrogen bonds via semioxalate anions. There are no direct cation–cation interactions via N—H...O hydrogen bonds between the ammonium and carboxylate groups, or via weaker S—H...S or S—H...O hydrogen bonds.     

Hydrogen‐bonding patterns in bis[2,4,6‐triazaniumylcyclohexane‐1,3,5‐tris(olate)‐κ3O,O′,O′′]germanium(IV) tetrachloride hexahydrate

A first preliminary report on the crystal structure of a hydrated salt formulated as [Ge(taci)₂]Cl₄·13H₂O (taci is 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol) appeared more than 20 years ago [Ghisletta (1994). PhD thesis, ETH Zürich. Switzerland]. At that time it was not possible to discriminate unambiguously between the positions of some of the chloride ions and water O atoms, and disorder was thus postulated. In a new determination, a conclusive scheme of hydrogen bonding proves to be a particularly appealing aspect of the structure. Single crystals of the title compound, C₁₂H₃₀GeN₆O₆⁴⁺·4Cl⁻·6H₂O or [Ge(taci)₂]₂Cl₈·12H₂O, were grown from an aqueous solution by slow evaporation of the solvent. The two [Ge(taci)₂]⁴⁺ cations exhibit a double‐adamantane‐type structure with exclusive O‐atom coordination and approximate D_3d symmetry. The taci ligands adopt a zwitterionic form with deprotonated hydroxy groups and protonated amino groups. Both cations are hydrogen bonded to six water molecules. The structure of the hydration shell of the two cations is, however, slightly different. The {[Ge(taci)₂]·6H₂O}⁴⁺ aggregates are interlinked in all three dimensions by further hydrogen bonds of the types N—H...Cl...H—N, N—H...O(H)₂...H—N, (Ge)O...H—O(H)...H—N, N—H...O(H)—H...Cl...H—N, (Ge)O...H—O—H...Cl...H—N, N—H...O(H)—H...Cl...H—(H)O...H—N, (Ge)O...H—O—H...Cl...H—(H)O...H—N and Ge(O)...H—O—H...Cl...H—O—H...O(Ge).     

Monoclinic and orthorhombic polymorphs of 4,4′,6,6′‐tetrachloro‐2,2′‐(piperazine‐1,4‐diyldimethylene)diphenol

The title compound, C₁₈H₁₈Cl₄N₂O₂, crystallizes as monoclinic and orthorhombic polymorphs from CHCl₃–CH₃OH solution. In both polymorphic forms, the molecule lies on a crystallographic centre of inversion (at the piperazine ring centroid) and exhibits an intramolecular O—H...N hydrogen bond. In the monoclinic polymorph (space group P2₁/c), the molecules are linked by intermolecular C—H...Cl hydrogen bonds into a ribbon sheet built from R₈⁸(34) rings. In the orthorhombic polymorph (space group Pbcn), the molecules are linked by intermolecular C—H...O hydrogen bonds into a ribbon sheet of R₆⁶(34) rings. The sheets in the orthorhombic polymorph are crosslinked into a three‐dimensional framework by π–π stacking interactions.     

Polymorphism of mer‐μ‐oxalato‐bis[chloridotripyridinecobalt(II)] pyridine disolvate

Single crystals of a triclinic polymorphic form of mer‐μ‐oxalato‐bis[chloridotripyridinecobalt(II)] pyridine disolvate, [Co₂(C₂O₄)Cl₂(C₅H₅N)₆]·2C₅H₅N, have been prepared by solvothermal methods. The structure and geometric parameters strongly resemble those of the previously reported monoclinic polymorph [Bolte (2006). Acta Cryst. E 62 , m597–m598]. In both polymorphic forms, the dinuclear complex molecules are located on a crystallographic centre of inversion, with the Co^II cations in a distorted octahedral environment consisting of a chloride ligand, three pyridine ligands and a chelating bis‐bidentate oxalate ligand. This last serves as a bridging ligand between two Co^II cations. The polymorphs differ in the mutual orientation of their pyridine ligands in the dinuclear molecules and in their intermolecular connectivity. In the triclinic polymorph, C—H...O, C—H...Cl, C—H...π and π–π interactions link the dinuclear molecules into a three‐dimensional structure. Pyridine solvent molecules are attached to this structure via weak interactions.     

Polymorphism in 2‐(4‐hydroxy‐2,6‐dimethylanilino)‐5,6‐dihydro‐4H‐1,3‐thiazin‐3‐ium chloride

Details of the structures of two conformational polymorphs of the title compound, C₁₂H₁₇N₂OS⁺·Cl⁻, are reported. In form (I) (space group P), the two N—H groups of the cation are in a trans conformation, while in form (II) (space group P2₁/c), they are in a cis arrangement. This results in different packing and hydrogen‐bond arrangements in the two forms, both of which have extended chains lying along the a direction. In form (I), these chains are composed of centrosymmetric R₄²(18) (N—H...Cl and O—H...Cl) hydrogen‐bonded rings and R₂²(18) (N—H...O) hydrogen‐bonded rings. In form (II), the chains are formed by centrosymmetric R₄²(18) (N—H...Cl and O—H...Cl) hydrogen‐bonded rings and by R₄²(12) (N—H...Cl) hydrogen‐bonded rings.     

1,2‐Bis[(pyridin‐2‐ylmethyl)sulfanyl]ethane and its dimorphic hydrochloride salt

Although having been described as a liquid in the literature for 41 years, 1,2‐bis[(pyridin‐2‐ylmethyl)sulfanyl]ethane, C₁₄H₁₆N₂S₂, (I), has now been obtained as monoclinic crystals via a new and convenient method of purification. Molecules of (I) are located on crystallographic inversion centres and are held together by C—H...N and C—H...S interactions, resulting in the formation of a three‐dimensional network structure. In addition, two polymorphs of the corresponding hydrochloride salt, 2‐[({2‐[(pyridin‐1‐ium‐2‐ylmethyl)sulfanyl]ethyl}sulfanyl)methyl]pyridin‐1‐ium dichloride, C₁₄H₁₈N₂S₂²⁺·2Cl⁻, (II) and (III), have been isolated. Molecules of (II) and (III) have similar conformations and are located on inversion centres. Both polymorphs form three‐dimensional networks through N—H...Cl, C—H...Cl and C—H...S interactions. The structure of (III) displays voids of 35 ų.     

A new three‐dimensional CdII supramolecular framework constructed from the 1‐[(1H‐tetrazol‐5‐yl)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane ligand

A new tetrazole–metal supramolecular compound, di‐μ‐chlorido‐bis(trichlorido{1‐[(1H‐tetrazol‐5‐yl‐κN²)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane}cadmium(II)), [Cd₂(C₈H₁₆N₆)₂Cl₈], has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. In the structure, each Cd^II cation is coordinated by five Cl atoms (two bridging and three terminal) and by one N atom from the 1‐[(1H‐tetrazol‐5‐yl)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane ligand, adopting a slightly distorted octahedral coordination geometry. The bridging bicyclo[2.2.2]octane and chloride ligands link the Cd^II cations into one‐dimensional ribbon‐like N—H...Cl hydrogen‐bonded chains along the b axis. An extensive hydrogen‐bonding network formed by N—H...Cl and C—H...Cl hydrogen bonds, and interchain π–π stacking interactions between adjacent tetrazole rings, consolidate the crystal packing, linking the poymeric chains into a three‐dimensional supramolecular network.     

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.     

Polymorphic forms of lupane triterpenoid betulonic aldehyde (betulonal)

The lupane triterpenoid betulonic aldehyde [also known as betulonal; systematic name: lup‐20(29)‐en‐28‐al‐3‐one, C₃₀H₄₆O₂] is a product of betulin oxidation. Crystals were obtained from hexane [form (I)] and dimethyl sulfoxide [form (II)] solutions. Forms (I) and (II) are both orthorhombic. The molecular geometric parameters in the two forms are similar, but the structures are different with respect to the crystal packing. Polymorph (I) contains two independent molecules in the asymmetric unit, while polymorph (II) contains only one molecule, which has a disordered aldehyde group [the disorder ratio is 0.769 (4):0.231 (4)]. In each molecule, the six‐membered rings have chair conformations, whereas the cyclopentane ring in each molecule adopts an envelope conformation. All the rings in the lupane nucleus are trans‐fused. The extended structures of both polymorphs are stabilized by weak intermolecular C—H...O and van der Waals interactions. Weak intramolecular C—H...O interactions are also observed.     

Two polymorphs of 1,8‐dichloroanthracene

A second, monoclinic, polymorph of the title compound, C₁₄H₈Cl₂, has been found. In addition to the structure of this monoclinic form, the structure of the previously described orthorhombic form [Desvergne, Chekpo & Bouas‐Laurent (1978). J. Chem. Soc. Perkin Trans. 2, pp. 84–87; Benites, Maverick & Fronczek (1996). Acta Cryst. C 52 , 647–648] has been redetermined at low temperature and using modern methods. The low‐temperature structure of the orthorhombic form is of significantly higher quality than the previously published structure and additional details can be derived. A comparison of the crystal packing of the two forms with a focus on weak intermolecular C—H...Cl interactions shows the monoclinic structure to have one such interaction linking the molecules into infinite ribbons, while two crystallographically independent C—H...Cl interactions give rise to an interesting infinite three‐dimensional network in the orthorhombic crystal form.     

Two novel polymorphic forms of iron‐chelating agent deferiprone

Thalassemia is a genetic blood disorder requiring life‐long blood transfusions. This process often results in iron overload and can be treated by an iron‐chelating agent, like deferiprone (3‐hydroxy‐1,2‐dimethylpyridin‐4‐one), C₇H₉NO₂, in an oral formulation. The first crystal structure of deferiprone, (Ia), was reported in 1988 [Nelson et al. (1988). Can. J. Chem. 66 , 123–131]. In the present study, two novel polymorphic forms, (Ib) and (Ic), of deferiprone were identified concomitantly with polymorph (Ia) during the crystallization experiments. Polymorph (Ia) was redetermined at low temperature for comparison of the structural features and lattice energy values with polymorphs (Ib) and (Ic). Polymorph (Ia) crystallized in the orthorhombic space group Pbca, whereas both polymorphs (Ib) and (Ic) crystallized in the monoclinic space group P2₁/c. The asymmetric units of (Ia) and (Ib) contain one deferiprone molecule, while polymorph (Ic) has three crystallographically independent molecules (A, B and C). All three polymorphs have similar hydrogen‐bonding features, such as an R₂²(10) dimer formed by O—H…O hydrogen bonds, an R₄³(20) tetramer formed by C—H…O hydrogen bonds and π–π interactions, but the polymorphs differ in their molecular arrangements in the solid state and are classified as packing polymorphs. O—H…O and C—H…O hydrogen bonds lead to the formation of two‐dimensional hydrogen‐bonded parallel sheets which are interlinked by π–π stacking interactions. In the three‐dimensional crystal packing, the deferiprone molecules were aggregated as corrugated sheets in polymorphs (Ia) and (Ic), whereas in polymorph (Ib), they were aggregated as a square‐grid network. The characteristic crystalline peaks of polymorphs (Ia), (Ib) and (Ic) were established through powder X‐ray diffraction analysis. The Rietveld analysis was also performed to estimate the contribution of the polymorphs to the bulk material.     

Four stereoisomers of the novel μ‐opioid receptor agonist tapentadol hydrochloride

The crystal and molecular structures of four stereoisomers of tapentadol hydrochloride [systematic name: 3‐(3‐hydroxyphenyl)‐N,N,2‐trimethylpentan‐1‐aminium chloride], C₁₄H₂₄NO⁺·Cl⁻, a novel analgesic agent, have been determined by X‐ray crystal structure analysis. Resolution of the isomers was carried out by reverse‐phase and chiral high‐performance liquid chromatographic (HPLC) methods. Stereoisomers (I) and (II) crystallize in the monoclinic space group P2₁, each with two tapentadol cations and two chloride anions in the asymmetric unit, while stereoisomers (III) and (IV) crystallize in the orthorhombic space group P2₁2₁2₁, with one tapentadol cation and one chloride anion in the asymmetric unit. The absolute configurations of the four enantiomers were determined unambiguously by X‐ray crystallography. The crystal structures reveal the stereochemistries at the 3‐ethyl and 2‐methyl groups to be R,R, S,S, S,R and R,S in stereoisomers (I)–(IV), respectively. The ethyl and aminopropyl groups adopt different orientations with respect to the phenol ring for (I) and (IV). In all four structures, the chloride ions take part in N—H...Cl and O—H...Cl hydrogen bonds with the tapentadol molecules, resulting in one‐dimensional helical chains in the crystal packing in each case.     

Two polymorphs of tris(ethylenediamine)cobalt(III) tetrathioantimonate(V)

Details of the structures of two polymorphs of tris(ethylenediamine)cobalt(III) tetrathioantimonate(V), [Co(C₂H₈N₂)₃][SbS₄], are reported. The first polymorph crystallizes in the orthorhombic space group Pna2₁, whereas the second polymorph belongs to the tetragonal space group P4₂bc. Both structures contain octahedral [Co(en)₃]³⁺ cations (en is ethylenediamine) and tetrahedral [SbS₄]³⁻ anions, which are interconnected via various N—H...S hydrogen bonds to form two different types of three‐dimensional network.     

Two new polymorphs of 2,6‐diaminopyrimidin‐4(3H)‐one monohydrate

The title compound, C₄H₆N₄O·H₂O, crystallized simultaneously as a triclinic and a monoclinic polymorph from an aqueous solution of 2,4‐diaminopyrimidin‐6‐ol. Previously, an orthorhombic polymorph was isolated under the same experimental conditions. The molecular geometric parameters in the two present polymorphs and the previously reported orthorhombic polymorph are similar, but the structures differ in the details of their crystal packing. In the triclinic system, the diaminopyrimidinone molecules are connected to one another via N—H...O and N—H...N hydrogen bonding to form infinite chains in the [011] direction. The chains are further hydrogen bonded to the water molecules, resulting in a three‐dimensional network. In the monoclinic system, the diaminopyrimidinone molecules are hydrogen bonded together into two‐dimensional networks parallel to the bc plane. The water molecules link the planes to form a three‐dimensional polymeric structure.     

Constructor graph description of hydrogen bonding in a supramolecular assembly of (3,5‐dimethyl‐1H‐pyrazol‐4‐ylmethyl)isopropylammonium chloride monohydrate

Five distinct strong hydrogen‐bonding interactions of four kinds (N—H...Cl, N—H...O, O—H...N, and O—H...Cl) connect molecules of the title compound, C₉H₁₈N₃⁺·Cl⁻·H₂O, in the crystal structure into corrugated sheets stacked along the a axis. The intermolecular interactions are efficiently described in terms of the first‐ through fifth‐level graph sets. A two‐dimensional constructor graph helps visualize the supramolecular assembly.     

Two polymorphs of N‐(2,6‐difluorophenyl)formamide

The structures of two distinct polymorphic forms of N‐(2,6‐difluorophenyl)formamide, C₇H₅F₂NO, have been studied using single crystals obtained under different crystallizing conditions. The two forms crystallize in different space groups, viz. form (Ia) in the orthorhombic Pbca and form (Ib) in the monoclinic P2₁ space group. Each polymorph crystallizes with one complete molecule in the asymmetric unit and they have a similar molecular geometry, showing a trans conformation with the formamide group being out of the plane of the aromatic ring. The packing arrangements of the two polymorphs are quite different, with form (Ia) having molecules that are stacked in an alternating arrangement, linked into chains of N—H...O hydrogen bonds along the crystallographic a direction, while form (Ib) has its N—H...O hydrogen‐bonded molecules stacked in a linear fashion. A theoretical study of the two structures allows information to be gained regarding other contributing interactions, such as π–π and weak C—H...F, in their crystal structures.     

The diastereoisomers 2‐[(S/R)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile at 100 K

In the structures of the two enantiopure diastereoisomers of the title compound, C₂₀H₁₈ClN₃O, which crystallize in different space groups, the molecules are very similar as far as bond distances and angles are concerned, but more substantial differences are observed in some torsion angles. The crystal structures of both molecules can be described as zigzag layers along the c axis. The packing is stabilized by hydrogen‐bond interactions of N—H...O, C—H...Cl and C—H...π types for 2‐[(R)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile, and of N—H...N, C—H...O and C—H...π types for 2‐[(S)‐2‐chloro‐3‐quinolyl]‐2‐[(R)‐1‐(4‐methoxyphenyl)ethylamino]acetonitrile, resulting in the formation of two‐ and three‐dimensional networks.