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.     

A comparative study of two polymorphs of L‐aspartic acid hydrochloride

Two polymorphs of L‐aspartic acid hydrochloride, C₄H₈NO₄⁺·Cl⁻, were obtained from the same aqueous solution. Their crystal structures have been determined from single‐crystal data collected at 100 K. The crystal structures revealed three‐ and two‐dimensional hydrogen‐bonding networks for the triclinic and orthorhombic polymorphs, respectively. The cations and anions are connected to one another via N—H...Cl and O—H...Cl interactions and form alternating cation–anion layer‐like structures. The two polymorphs share common structural features; however, the conformations of the L‐aspartate cations and the crystal packings are different. Furthermore, the molecular packing of the orthorhombic polymorph contains more interesting interactions which seems to be a favourable factor for more efficient charge transfer within the crystal.     

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.     

Positional isomeric effect on the crystallization of chlorine‐substituted N‐phenyl‐2‐phthalimidoethanesulfonamide derivatives

The ortho‐, para‐ and meta‐chloro‐substituted N‐chlorophenyl‐2‐phthalimidoethanesulfonamide derivatives, C₁₆H₁₃ClN₂O₄S, have been structurally characterized by single‐crystal X‐ray crystallography. N‐(2‐Chlorophenyl)‐2‐phthalimidoethanesulfonamide, (I), has orthorhombic (P2₁2₁2₁) symmetry, N‐(4‐chlorophenyl)‐2‐phthalimidoethanesulfonamide, (II), has triclinic (P) symmetry and N‐(3‐chlorophenyl)‐2‐phthalimidoethanesulfonamide, (III), has monoclinic (P2₁/c) symmetry. The molecules of (I)–(III) are regioisomers which have crystallized in different space groups as a result of the differing intra‐ and intermolecular hydrogen‐bond interactions which are present in each structure. Compounds (I) and (II) are stabilized by N—H...O and C—H...O hydrogen bonds, while (III) is stabilized by N—H...O, C—H...O and C—H...Cl hydrogen‐bond interactions. The structure of (II) also displays π–π stacking interactions between the isoindole and benzene rings. All three structures are of interest with respect to their biological activities and have been studied as part of a programme to develop anticonvulsant drugs for the treatment of epilepsy.     

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.     

Conformational polymorphs of 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole

The dipharmacophore compound 3‐cyclopropyl‐5‐(3‐methyl‐[1,2,4]triazolo[4,3‐a]pyridin‐7‐yl)‐1,2,4‐oxadiazole, C₁₂H₁₁N₅O, was studied on the assumption of its potential biological activity. Two polymorphic forms differ in both their molecular and crystal structures. The monoclinic polymorphic form was crystallized from more volatile solvents and contains a conformer with a higher relative energy. The basic molecule forms an abundance of interactions with relatively close energies. The orthorhombic polymorph was crystallized very slowly from isoamyl alcohol and contains a conformer with a much lower energy. The basic molecule forms two strong interactions and a large number of weak interactions. Stacking interactions of the `head‐to‐head' type in the monoclinic structure and of the `head‐to‐tail' type in the orthorhombic structure proved to be the strongest and form stacked columns in the two polymorphs. The main structural motif of the monoclinic structure is a double column where two stacked columns interact through weak C—H…N hydrogen bonds and dispersive interactions. In the orthorhombic structure, a single stacked column is the main structural motif. Periodic calculations confirmed that the orthorhombic structure obtained by slow evaporation has a lower lattice energy (0.97 kcal mol^?1) compared to the monoclinic structure.     

Weak intermolecular interactions in 11‐chloro‐2,3,4,5‐tetrahydro‐1H‐cyclohepta[b]quinoline

The title compound, C₁₄H₁₄ClN, is a chloro analogue of tacrine, an acetylcholinesterase inhibitor. The compound comprises a seven‐membered alicyclic ring whose CH donor groups are engaged in extensive intermolecular interactions. The important feature of this crystal structure is that, regardless of the presence of two typical hydrogen‐bonding acceptors, viz. chlorine and nitrogen, the corresponding C—H...Cl and C—H...N interactions take no significant role in crystal stabilization. The molecules form dimers through π–π interactions with an interplanar distance between interacting pyridine rings of 3.576 (1) Å. Within the dimers, the molecules are additionally interconnected by four C—H...π interactions. The dimers arrange into regular columns via further intermolecular C—H...π interactions.     

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.     

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.     

Three quinolone compounds featuring O...I halogen bonding

Ethyl 1‐ethyl‐6‐iodo‐4‐oxo‐1,4‐dihydroquinoline‐3‐carboxylate, C₁₄H₁₄INO₃, (I), and ethyl 1‐cyclopropyl‐6‐iodo‐4‐oxo‐1,4‐dihydroquinoline‐3‐carboxylate, C₁₅H₁₄INO₃, (II), have isomorphous crystal structures, while ethyl 1‐dimethylamino‐6‐iodo‐4‐oxo‐1,4‐dihydroquinoline‐3‐carboxylate, C₁₄H₁₅IN₂O₃, (III), possesses a different solid‐state supramolecular architecture. In all three structures, O...I halogen‐bonding interactions connect the quinolone molecules into infinite chains parallel to the unique crystallographic b axis. In (I) and (II), these molecular chains are arranged in (101) layers, viaπ–π stacking and C—H...π interactions, and these layers are then interlinked by C—H...O interactions. The structural fragments involved in the C—H...O interactions differ between (I) and (II), accounting for the observed difference in planarity of the quinolone moieties in the two isomorphous structures. In (III), C—H...O and C—H...π interactions form (100) molecular layers, which are crosslinked by O...I and C—H...I interactions.     

Supramolecular networks in (9‐fluoro‐4H‐chromeno[4,3‐c]isoxazol‐3‐yl)methanol and its 9‐chloro analogue at 100 K

The title compounds, (9‐fluoro‐4H‐chromeno[4,3‐c]isoxazol‐3‐yl)methanol, C₁₁H₈FNO₃, (I), and (9‐chloro‐4H‐chromeno[4,3‐c]isoxazol‐3‐yl)methanol, C₁₁H₈ClNO₃, (II), crystallize in the orthorhombic space group Pbca with Z′ = 1 and the triclinic space group P with Z′ = 6, respectively. The simple replacement of F by Cl in the main molecular scaffold of (I) and (II) results in significant differences in the intermolecular interaction patterns and a corresponding change in the point‐group symmetry from D_2h to C_i = S₂. These striking differences are manifested through the presence of C—H...F and the absence of O—H...O and C—H...O interactions in (I), and the absence of C—H...Cl and the presence of O—H...O and C—H...O interactions in (II). However, the geometry of the synthons formed by the O—H...N and O—H...X (X = F or Cl) interactions observed in the constitution of the supramolecular networks of both (I) and (II) remains similar. Also, C—H...O interactions are not preferred in the presence of F in (I), while they are much preferred in the presence of Cl in (II).     

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.     

Chlorido(2,3,7,8,12,13,17,18‐octaethylporphyrinato)iron(III): a new triclinic polymorph of Fe(OEP)Cl

The previous structure determination of the title compound, [Fe(C₃₆H₄₄N₄)Cl], was of a monoclinic polymorph [Senge (2005). Acta Cryst. E 61 , m399–m400]. The crystal structure of a new triclinic polymorph has been determined based on single‐crystal X‐ray diffraction data collected at 100 K. The asymmetric unit contains one molecule of the high‐spin square‐pyramidal iron(III) porphyrinate. The structure exhibits distinct nonstatistical alternative positions for most atoms and was consequently modeled as a whole‐molecule disorder. The compound is characterized by an average Fe—N bond length of 2.065 (2) Å, an Fe—Cl bond length of 2.225 (4) Å, and the iron(III) cation displaced by 0.494 (4) Å from the plane of the 24‐atom porphyrinate core, essentially the same as in the previously determined polymorph. Common features of the porphyrin plane–plane stacking involve two types of synthons, each of which can be further stabilized with additional H...Cl interactions to the axial chloride ligand, exhibiting concerted interactions of H atoms from the ethyl groups with the π‐cloud electron density of adjacent molecules; the shortest methylene H‐atom contacts are in the range 2.75–2.91 Å, resulting in plane–plane separations of 3.407 (4) and 3.416 (4) Å, and the shortest methyl H‐atom contacts are 2.56–2.95 Å, resulting in plane–plane separations of 4.900 (5) and 4.909 (5) Å in the monoclinic polymorph. The plane‐to‐plane stacking synthons in the triclinic polymorph are similar, but at greater distances; the shortest methylene H‐atom contacts are 2.86–2.94 Å, resulting in plane–plane separations of 3.45 (2) and 3.45 (3) Å, and the shortest methyl H‐atom contacts are 2.89–3.20 Å, resulting in plane–plane separations of 5.081 (13) and 5.134 (13) Å, consistent with the density of the triclinic polymorph being 1.5% lower, suggesting lesser packing efficiency and lower stability in the triclinic polymorph. The major molecular differences found in the polymorphs is in three different orientations of the ethyl‐group side chains on the periphery of the porphyrin core.     

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.     

Probing the relationships between molecular conformation and intermolecular contacts in N,N‐dibenzyl‐N′‐(furan‐2‐carbonyl)thiourea

In the crystal structure of the title compound, C₂₀H₁₈N₂O₂S, molecules are linked by bifurcated C—H...O hydrogen‐bond interactions, giving rise to chains whose links are composed of alternating centrosymmetrically disposed pairs of molecules and characterized by R₂²(10) and R₂²(20) hydrogen‐bonding motifs. Also, N—H...S hydrogen bonds form infinite zigzag chains along the [010] direction, which exhibit the C(4) motif. Hirshfeld surface and fingerprint plots were used to explore the intermolecular interactions in the crystal structure. This analysis confirms the important role of C—H...O hydrogen bonds in the molecular conformation and in the crystal structure, providing a potentially useful tool for a full understanding of the intermolecular interactions in acylthiourea derivatives.     

Two different modes of halogen bonding in two 4‐nitroimidazole derivatives

In the crystal structures of the two imidazole derivatives 5‐chloro‐1,2‐dimethyl‐4‐nitro‐1H‐imidazole, C₅H₆ClN₃O₂, (I), and 2‐chloro‐1‐methyl‐4‐nitro‐1H‐imidazole, C₄H₄ClN₃O₂, (II), C—Cl...O halogen bonds are the principal specific interactions responsible for the crystal packing. Two different halogen‐bond modes are observed: in (I), there is one very short and directional C—Cl...O contact [Cl...O = 2.899 (1) Å], while in (II), the C—Cl group approaches two different O atoms from two different molecules, and the contacts are longer [3.285 (2) and 3.498 (2) Å] and less directional. In (I), relatively short C—H...O hydrogen bonds provide the secondary interactions for building the crystal structure; in (II), the C—H...O contacts are longer but there is a relatively short π–π contact between molecules related by a centre of symmetry. The molecule of (I) is almost planar, the plane of the nitro group making a dihedral angle of 6.97 (7)° with the mean plane of the imidazole ring. The molecule of (II) has crystallographically imposed mirror symmetry and the nitro group lies in the mirror plane.     

5:1 and 2:1 cocrystals of 2,3,4,5,6‐pentafluorophenol with phenazine

2,3,4,5,6‐Pentafluorophenol (pFp), unlike phenol, forms cocrystals with the weak heteroaromatic base phenazine (phz). Two types of cocrystals were prepared, (I) with a high content of pFp, 2,3,4,5,6‐pentafluorophenol–phenazine (5/1), 5C₆HF₅O·C₁₂H₈N₂, and (II) with a 2:1 pFp–phz molar ratio, 2,3,4,5,6‐pentafluorophenol–phenazine (2/1), 2C₆HF₅O·C₁₂H₈N₂. In both forms, homostacks are formed by the heterocyclic base and phenol molecules and no aryl–perfluoroaryl stacking interactions occur. The arrangement of the molecules in the crystal of (I) is determined by strong O—H...N and O—H...O hydrogen bonds, weak O—H...F, C—H...F and C—H...O interactions, π–π stacking interactions between the phz molecules and C—F...π_F interactions within the pFp stacks. Among the specific interactions in (II) are a strong O—H...N hydrogen bond, weak C—H...F interactions and π–π stacking interactions between the phz molecules. In (I) and (II), the heterocyclic molecules are located around inversion centres and one of the symmetry‐independent pFp molecules in (I) is disordered about an inversion centre. Remarkably, similar structural fragments consisting of six pFp stacks can be identified in cocrystal (I) and in the known orthorhombic polymorph of pFp with Z′ = 3 [Gdaniec (2007). CrystEngComm, 9 , 286–288].     

Chiral crystals from an achiral molecule: 4,6‐di‐O‐benzyl‐1,3‐O‐benzylidene‐2‐O‐(4‐methoxybenzyl)‐myo‐5‐inosose

The title achiral compound, C₃₅H₃₄O₇, crystallizes in the chiral monoclinic space group P2₁. The molecules are densely packed to form a helical assembly along the crystallographic twofold screw axis via C—H...O and C—H...π interactions. Interestingly, the unit‐translated helical chains are loosely connected via a rather uncommon edge‐to‐edge Ph—H...H—Ph short contact (H...H = 2.33 Å).     

Syntheses and Characterization of New Copper Complexes with the Heterocyclic Thione,AMTTO. X‐Ray Structures of [Cu(AMTTO)Cl2], [Cu(AMTTO)2]Cl,and [Cu(AMTTO)(PPh3)2Cl] (AMTTO = 4‐Amino‐6‐methyl‐1, 2, 4‐triazine‐3‐thione‐5‐one)

The complexes [Cu(AMTTO)Cl₂] ( 2 ), [Cu(AMTTO)₂]Cl ( 3 ), and [Cu(AMTTO)(PPh₃)₂Cl] ( 4 ) have been prepared and characterized by IR spectroscopy and elemental analyses. Also single‐crystal X‐ray diffraction studies on compound 2 , 3 and 4 revealed that AMTTO acts in 2 as a bidentate ligand via nitrogen and sulfur atoms, in 3 and 4 as a monodentate via sulfur atoms. Complex 3 was already mentioned in literature, but the structure was not described in detail. The molecules in 2 form infinite chains through additional weak Cu—S interactions along [010] indicating the Jahn‐Teller distortion of the d⁹ ion Cu²⁺. The infinite chains are connected by hydrogen bonding along [100]. Crystal data for 2 at —80°C: monoclinic, space group P2₁/m, a = 666.7(1), b = 609.4(1), c = 1132.6(2) pm, b = 95.46(2)°, Z = 2, R₁ = 0.0365; for 3 at —80°C: orthorhombic, space group Pbcn, a = 1291.2(2), b = 1146.5(1), c = 1000.5(1) pm, Z = 4, R₁ = 0.0315; for 4 at —80°C: monoclinic, space group, P2₁/n, a = 879.4(1), b = 1849.3(2), c = 2293.8(3) pm, β = 92.38(1)°, Z = 4, R₁ = 0.0688.