l‐Alanylglycyl‐l‐alanine monohydrate at 20 K

The X‐ray crystal structure of the title compound, C₈H₁₅N₃O₄·H₂O, at 20 K (space group P2₁) reveals that the mol­ecular conformation of the tripeptide is remarkably different from the water‐free form (space group P2₁2₁2₁) reported previously [Padiyar & Seshadri (1996), Acta Cryst. C 52 , 1693–1695].     

l‐Methioninium chloride and l‐seleno­methioninium chloride at 103 K

The crystal structures of the title compounds, (S)‐1‐carboxy‐3‐(methyl­sulfanyl)­propanaminium chloride, C₅H₁₂NO₂S⁺·Cl⁻, and (S)‐1‐carboxy‐3‐(methyl­selanyl)­propanaminium chloride, C₅H₁₂NO₂Se⁺·Cl⁻, are isomorphous. The proton­ated l ‐methionine and l ‐seleno­methionine mol­ecules have almost identical conformations and create very similar contacts with the Cl⁻ anions in the crystal structures of both compounds. The amino acid cations and the Cl⁻ anions are linked viaN—H⋯Cl⁻ and O—H⋯Cl⁻ hydrogen bonds.     

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].     

Barium(II)–2,4‐dinitrophenolate–18‐crown‐6 at 183 K

The title compound, bis(2,4‐dinitrophenolato‐κ²O,O′)(1,4,7,10,13,16‐hexaoxadecane‐κ⁶O)barium(II), [Ba(C₆H₃N₂O₅)₂(C₁₂H₂₄O₆)], is a 1:1 complex of barium(II)–2,4‐di­nitro­phenolate and 1,4,7,10,13,16‐hexaoxa­cyclo­octa­decane (18‐crown‐6). Its structure is located on a crystallographic inversion centre. The temperature dependence of the crystal structure has been studied. The monoclinic β angle of the P2₁/­n space group increases with increasing temperature. The packing structure of the complex is stabilized by intermolecular C—H?O interactions.     

Polymorphism of l‐Tryptophan

A new polymorph of l ‐tryptophan was prepared through crystallization from the gas phase, with structure determination carried out directly from powder XRD data augmented by periodic DFT‐D calculations. The new polymorph (denoted β) and the previously reported polymorph (denoted α) are both based on alternating hydrophilic and hydrophobic layers, but with substantially different hydrogen‐bonding arrangements. The β polymorph exhibits the energetically favourable l 2‐l 2 hydrogen‐bonding arrangement, which is unprecedented for amino acids with aromatic side chains. The specific molecular conformations adopted in the β polymorph facilitate this hydrogen‐bonding scheme while avoiding steric conflict of the side chains.     

N‐Benzylformamide at 150 K

The title compound, C₈H₉NO, crystallizes with Z′ = 2. Each type of independent molecule links into a separate N—H...O hydrogen‐bonded chain in the a‐axis direction. There are also three weak C—H...O hydrogen bonds, which join the molecules into a two‐dimensional sheet parallel to (001). The molecules exhibit the trans conformation of the –NHCHO group and an anti conformation around the (Ph)C—NH(CHO) bond. The formamide group in each of the symmetry‐independent molecules is twisted out of the benzyl group plane, forming angles of 75.96 (10) and 65.23 (11)° with this plane. The significance of this study lies in the comparison drawn between the experimental and calculated data of the crystal structure of the title compound and the data of several other derivatives possessing the –CH₂—NH—CO– group. The correlation between the IR spectrum of this compound and the hydrogen‐bond energy is also discussed. This molecular system is of particular interest to biochemists because of its preventative function against toxic products of alcohols in human metabolism.     

Quinolin‐6‐ol at 100 K

The title compound, C₉H₇NO, has two symmetry‐independent molecules in the asymmetric unit, which have different conformations of the hydroxy group with respect to the quinoline ring. One of the molecules adopts a cis conformation, while the other shows a trans conformation. Each type of independent molecule links into a separate infinite O—H...N hydrogen‐bonded chain with the graph‐set notation C(7). These chains are perpendicular in the unit cell, one extended in the a‐axis direction and the other in the b‐axis direction. There is also a weak C—H...O hydrogen bond with graph‐set notation D(2), which runs in the c‐axis direction and joins the two separate O—H...N chains. The significance of this study lies in the comparison drawn between the experimental and calculated data of the crystal structure of the title compound and the data of several other derivatives possessing the hydroxy group or the quinoline ring. The correlation between the IR spectrum of this compound and the hydrogen‐bond energy is also discussed.     

Sulfapyridine (polymorph III), sulfapyridine dioxane solvate,sulfapyridine tetrahydrofuran solvate and sulfapyridine piperidine solvate,all at 173 K

The X‐ray crystal structures of solvates of sulfapyridine have been determined to be conformational polymorphs. 4‐Amino‐N‐(1,2‐dihydropyridin‐2‐ylidene)benzenesulfonamide (polymorph III), C₁₁H₁₁N₃O₂S, (1), 4‐amino‐N‐(1,2‐dihydropyridin‐2‐ylidene)benzenesulfonamide 1,3‐dioxane monosolvate, C₁₁H₁₁N₃O₂S·C₄H₈O₂, (2), and 4‐amino‐N‐(1,2‐dihydropyridin‐2‐ylidene)benzenesulfonamide tetrahydrofuran monosolvate, C₁₁H₁₁N₃O₂S·C₄H₈O, (3), crystallized as the imide form, while piperidin‐1‐ium 4‐amino‐N‐(pyridin‐2‐yl)benzenesulfonamidate, C₅H₁₂N⁺·C₁₁H₁₀N₃O₂S⁻, (4), crystallized as the piperidinium salt. The tetrahydrofuran and dioxane solvent molecules in their respective structures were disordered and were refined using a disorder model. Three‐dimensional hydrogen‐bonding networks exist in all structures between at least one sulfone O atom and the aniline N atom.     

1,3,5‐Triiodo‐2,4,6‐trimethylbenzene at 293 K

In the structure of tri­iodo­mesityl­ene (1,3,5‐tri­iodo‐2,4,6‐tri­methyl­benzene), C₉H₉I₃, at 293 K, the benzene ring is found to be significantly distorted from ideal D_6h symmetry; the average endocyclic angles facing the I atoms and the methyl groups are 123.8 (3) and 116.2 (3)°, respectively. The angle between the normal to the molecular plane and the normal to the (100) plane is 5.1°. No disorder was detected at 293 K. The thermal motion was investigated by a rigid‐body motion tensor analysis. Intra‐ and intermolecular contacts are described and topological differences compared with the isomorphous compounds tri­chloro­mesityl­ene and tri­bromo­mesityl­ene are discussed.     

4‐Ethynyl‐1,2‐methylenedioxybenzene at 150 K

The title compound, C₉H₆O₂, contains two moderate C—H?O hydrogen bonds. That involving the terminal alkyne gives rise to chains along the b axis. The other hydrogen bond occurs over a centre of symmetry, leading to dimers. The combination of the two interactions gives rise to rings, each comprising six mol­ecules, which are part of infinite sheets in the bc plane.     

Di‐9‐anthryl disulfide at 193 K

The title compound, C₂₈H₁₈S₂, crystallizes in the monoclinic space group P2₁/n and the structure shows pseudosymmetry close to the space group C2/c. At 193 K the compound has a long S—S bond of 2.1089 (12) Å and the S atom to anthracene bond distances are 1.776 (3) and 1.770 (2) Å. The C—S—S—C torsion angle is 76.06 (13)°.     

dl‐Arginine monohydrate at 100 K

In the title compound, C₆H₁₄N₄O₂·H₂O, the α‐amino group is neutral. The molecular side chain including the guanidinium group is not fully extended, having a near gauche–gauche conformation [χ³ = 59.0 (1)°; χ⁴ = 72.8 (1)°]. The network of hydrogen bonds stabilizing the crystal lattice includes those formed between the deprotonated and negatively charged α‐carboxyl­ate groups and the positively charged amino groups of the guanidinium group of neighbouring mol­ecules. N—H?O=C and water‐mediated N—H?O hydrogen bonds link individual mol­ecules to produce pairs of spiral motifs laterally connected by N—H?O and C—H?O hydrogen bonds.     

N‐(l‐2‐Aminobutyryl)‐l‐alanine and 2‐(l‐alanylamino)‐l‐butyric acid 0.33‐hydrate

The crystal structure of N‐(l ‐2‐amino­butyryl)‐l ‐alanine, C₇H₁₄N₂O₃, is closely related to the structure of l ‐alanyl‐l ‐alanine, both being tetragonal, while the retro‐analogue 2‐(l ‐alanyl­amino)‐l ‐butyric acid 0.33‐hydrate, C₇H₁₄N₂O₃·­0.33H₂O, forms a new type of molecular columnar structure with three peptide mol­ecules in the asymmetric unit.     

2,4,5,7‐Tetra­methyl­phenanthrene at 150 K

The title compound, C₁₈H₁₈, crystallized in the centrosymmetric space group P2₁/c with one mol­ecule as the asymmetric unit. The methyl‐group H atoms at the 4 and 5 positions are ordered, while those at the 2 and 7 positions are disordered. The torsion of the bay region of the core is notably similar to that of other 4,5‐di­methyl­phenanthrenes. No substantial C—H?π interaction occurs in this structure.     

Redetermination of ternifoline‐C at 150 K

The relative stereochemistry of ternifoline‐C (7,20‐epoxy‐ent‐kaur‐16‐ene‐1,6,7,15‐tetrol 1‐acetate), C₂₂H₃₂O₆, previously reported by Wu [FudanXuebaoZir. Kex. (1988), 27 , 61–65], has been redetermined at 150 K. The molecular geometry and crystal packing agree well with the previous study.     

Redetermination of cis‐4‐cyclo­hexene‐1,2‐di­carboxyl­ic acid at 173 K

The structure of the title compound, C₈H₁₀O₄, previously determined by Küppers & Kim [Acta Cryst. (1993), C 49 , 1218–1220] has been redetermined at 173 K. The cyclo­hexene ring exhibits a half‐chair conformation. The molecular geometry and the crystal packing, which is stabilized by two hydrogen bonds, agree well with the room‐temperature structure determination.     

Low‐temperature study of 3‐acetylindole at 110 K

The title compound, C₁₀H₉NO, contains an acetyl group that is nearly coplanar with the indole ring system, with an angle between the planes of the heterocyclic ring and the acetyl group of 1.75 (17)°. The planes of the benzene and pyrrole rings in the indole system make a dihedral angle of 2.05 (11)°. Each molecule in the unit cell is linked through N—H...O hydrogen bonds to two other molecules, forming hydrogen‐bonded chains in the [101] direction with graph set C(6). The significance of this study lies in the analysis of the interactions occurring via hydrogen bonds in this structure, as well as in the comparison drawn between the molecular structure of the title compound and those of several other indole derivatives possessing a 3‐carbonyl group. The correlation between the IR spectrum of this compound and the structural data is also discussed.     

Acetone‐4‐methyl­thio­semicarbazone at 220 K

In the title compound, C₅H₁₁N₃S, the trans conformation is stabilized by a weak intramolecular N—H?N hydrogen bond. Unusually, one N—H bond is not involved in any hydrogen‐bond interactions and instead the mol­ecules form a one‐dimensional polymer via N—H?S intermolecular hydrogen bonds.     

Adiponitrile at 100 K

Adiponitrile, C₆H₈N₂, is a key intermediate in the synthesis of the polyamide Nylon 66 and is produced industrially on a large scale. We have determined the crystal and molecular structure of adiponitrile by single‐crystal X‐ray analysis at 100 K, a suitable crystal (m.p. 275 K) having been grown from the melt at low temperature. The compound crystallizes in the monoclinic space group P 2₁/c with Z = 2. In the crystal structure, the molecule adopts an exact C_i‐symmetric gauche –anti –gauche conformation of the C—C—C—C skeleton about an inversion centre. The molecules are densely packed, with short intermolecular contacts between the α‐H and nitrile N atoms.     

Thioacetanilide at 120 K

The title compound, C₈H₉NS, has four symmetry‐independent molecules in the asymmetric unit. These molecules link into two independent infinite N—H...S hydrogen‐bonded chains in the a‐axis direction with graph‐set notation C₂²(8). The NH—CS group adopts a trans conformation and forms a dihedral angle of about 50° with the phenyl ring. The intermolecular hydrogen‐bond energy calculated by the density functional theory (DFT) method is −14.95 kJ mol⁻¹. The correlation between the IR spectrum of this compound and the hydrogen‐bond energy is also discussed. This molecular system is of interest because of its biological function.