Magnesium sulfate hexahydrate at 120 K

The structure of [Mg(H₂O)₆]SO₄ was redetermined at 120 K, confirming the hydrogen‐bond pattern found at room temperature [Zalkin et al. (1964). Acta Cryst. 17 , 235–240] but showing the librational corrections of bond lengths to be unrealistic.     

Racemic dipeptide glycyl‐dl‐leucine at 120 K

The structure of glycyl‐dl ‐leucine, C₈H₁₆N₂O₃, has been determined at 120 K by single‐crystal X‐ray diffraction. In addition to three N—H?O‐type hydrogen bonds of the positively charged RNH₃⁺ group of the zwitterionic mol­ecule, an intermolecular N—H?O contact exists between the peptide bond and the carboxyl­ate group. Four hydrogen‐bond cycles were identified, giving a complex pattern.     

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.     

Phthal­imide at 120 K: perforated molecular ribbons containing three different ring motifs

Molecules of phthal­imide [1H‐iso­indole‐1,3(2H)‐dione], C₈H₅NO₂, are linked by N—H?O hydrogen bonds [H?O 2.02 Å, N?O 2.8781 (16) Å and N—H?O 167°] and by C—H?O hydrogen bonds [H?O 2.54 and 2.56 Å, C?O 3.3874 (18) and 3.4628 (19) Å, and C—H?O 149 and 159°] into molecular ribbons, which are pierced by three different ring motifs; there are two centrosymmetric R(8) rings, each containing a single hydrogen bond, N—H?O in one case and C—H?O in the other, and R(9) rings containing all three hydrogen bonds.     

A synchrotron‐radiation study of the lactone form of rhodamine B at 120 K

The structure of the lactone form of rhod­amine B, 3,6‐bis­(diethyl­amino)‐1′,3′‐di­hydro­spiro­[xanthene‐9,3′‐isobenzo­furan]‐1′‐one, C₂₈H₃₀N₂O₃, has been determined at 120 K using synchrotron radiation at a wavelength of 0.496 Å. The structure contains two independent rhod­amine B mol­ecules with virtually identical geometry. The xanthene main planes of the mol­ecules are inclined at an angle of 41.6 (2)° to one another. Molecule 2 has a statistically disordered ethyl group, with 71% in one orientation and 29% in a second orientation. The lactone C—O bonds are 1.497 (1) and 1.495 (1) Å. There are no classical hydrogen bonds, but the structure is stabilized by two short C?O interactions. The crystals of the lactone form were produced by a novel hydro­thermal reaction.     

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.     

Dirubidium dicadmium sulfate at 293 K

The structure of Rb₂Cd₂(SO₄)₃ at room temperature has been refined using X‐ray diffraction data. The structure is similar to that of other cubic langbeinites. However, the title compound differs from other type I langbeinites in that the bond‐valence sums of the metal cations (in particular the Rb atoms) are practically equal to their nominal chemical valences.     

Dibenzylammonium hydrogen maleate and a redetermination at 120 K of bis(dibenzylamino)methane

In dibenzylammonium hydrogen maleate [or dibenzylammonium (2Z)‐3‐carboxyprop‐2‐enoate], C₁₄H₁₆N⁺·C₄H₃O₄⁻, (I), the anion contains a fairly short and nearly linear O—H...O hydrogen bond, with an O...·O distance of 2.4603 (16) Å, but with the H atom clearly offset from the mid‐point of the O...O vector. The counter‐ions in (I) are linked by two N—H...O hydrogen bonds to form C₂²(6) chains and these chains are weakly linked into sheets by a C—H...O hydrogen bond. Bis(dibenzylamino)methane, C₂₉H₃₀N₂, (II), crystallizes with two independent molecules lying across twofold rotation axes in the space group C2/c, and the molecules are conformationally chiral; there are no direction‐specific intermolecular interactions in the crystal structure of (II).     

Two solid phases of pyrimidin‐1‐ium hydrogen chloranilate monohydrate determined at 225 and 120 K

The crystal structures of two solid phases of the title compound, C₄H₅N₂⁺·C₆HCl₂O₄⁻·H₂O, have been determined at 225 and 120 K. In the high‐temperature phase, stable above 198 K, the transition temperature of which has been determined by ³⁵Cl nuclear quadrupole resonance and differential thermal analysis measurements, the three components are held together by O—H...O, N...H...O, C—H...O and C—H...Cl hydrogen bonds, forming a centrosymmetric 2+2+2 aggregate. In the N...H...O hydrogen bond formed between the pyrimidin‐1‐ium cation and the water molecule, the H atom is disordered over two positions, resulting in two states, viz. pyrimidin‐1‐ium–water and pyrimidine–oxonium. In the low‐temperature phase, the title compound crystallizes in the same monoclinic space group and has a similar molecular packing, but the 2+2+2 aggregate loses the centrosymmetry, resulting in a doubling of the unit cell and two crystallographically independent molecules for each component in the asymmetric unit. The H atom in one N...H...O hydrogen bond between the pyrimidin‐1‐ium cation and the water molecule is disordered, while the H atom in the other hydrogen bond is found to be ordered at the N‐atom site with a long N—H distance [1.10 (3) Å].     

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.     

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.     

Lithium phospho­enolpyruvate monohydrate at 85 K

The crystal structure of the title compound, lithium (1‐carboxy­ethenyl­oxy)­phospho­nate monohydrate, Li⁺·C₃H₄O₆P^?·­H₂O, is governed by lithium–oxy­gen interactions and hydrogen bonds. The Li⁺ cation is tetrahedrally coordinated by phosphate and water O atoms. The phospho­enolpyruvate monoanions form carboxyl‐to‐carboxyl and phosphate‐to‐water hydrogen bonds.     

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.     

Partial ordering of tripivaloylmethane at 110 K

Tripivaloylmethane [systematic name: 4‐(2,2‐dimethylpropanoyl)‐2,2,6,6‐tetramethylheptane‐3,5‐dione], C₁₆H₂₈O₃, is known to crystallize at room temperature in the space group R3m with three molecules in the unit cell. The molecules are conformationally chiral and pack so that each molecular site is occupied with equal probability by the two enantiomers. Upon cooling to 110 K, the structure partially orders; two molecules in the unit cell order into two different conformations of opposite chirality, while the third remains disordered. The symmetry of the resulting crystal is P3, with each of the molecules lying about a different threefold rotation axis. This paper describes an unusual case of order–disorder phase transition in which the structure partially orders by changes of molecular conformation in the single crystals. Such behaviour is of interest in the study of phase transitions and molecular motion in the solid state.     

Polymeric tris(μ2‐acetone‐κ2O:O)sodium polyiodide at 120 K

In the title compound, [Na(C₃H₆O)₃]_n(I₂)_n, all non‐H atoms are in special positions of the space group P6₃/mcm, with the Na atom in 2b, the I atom in 4c, the carbonyl O atom and the C atom attached to it both in 6g, and the methyl C atom in 12k. The H atoms of the rotationally disordered methyl groups are in 24l general positions but with occupancies of 0.5, because they occur in two sets related by a crystallographic mirror plane. Infinite chains are created by face‐sharing octahedral Na‐coordination polyhedra, with Na—O and Na⋯Na distances of 2.439 (5) and 3.2237 (4) Å, respectively. I atoms form infinite linear chains, in which the I‐atom separation is 3.2237 (4) Å.     

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)°.     

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.     

Strontium diibuprofenate dihydrate,strontium malonate sesquihydrate,strontium diascorbate dihydrate and strontium 2‐oxidobenzoate hydrate at 120 K

Four strontium(II) salts with organic acids have been studied. Poly[diaquadi‐μ‐ibuprofenato‐strontium(II)] or poly­[diaqua­bis[μ‐2‐(4‐isobutyl­phen­yl)­propionato]­strontium(II)], [Sr(C₁₃H₁₇O₂)₂(H₂O)₂]_n, crystallizes with eight‐coordinated Sr atoms. The coordination polyhedra are inter­connected by edge‐sharing to form chains. The Sr coordination chains are packed into layers, which are stacked by van der Waals inter­actions. Poly[μ‐aqua‐diaquadi‐μ‐malonato‐distrontium(II)], [Sr₂(C₃H₂O₄)₂(H₂O)₃]_n, crystallizes with nine‐coordinated Sr atoms three‐dimensionally inter­connected into a framework structure. One of the two crystallographically independent water mol­ecules is located on a twofold axial site. catena‐Poly[[diaqua­(ascorbato)strontium(II)]‐μ‐ascorbato], [Sr(C₆H₇O₆)₂(H₂O)₂]_n, crystallizes with isolated eight‐coordinated Sr polyhedra. One of the ascorbate ligands bridges two Sr atoms, forming zigzag polyhedral ascorbate chains. These chains are tied together by a three‐dimensional hydrogen‐bonding network. Poly[aqua‐μ‐2‐oxidobenzoato‐strontium(II)], [Sr(C₇H₄O₃)(H₂O)]_n, crystallizes with eight‐coordinated Sr atoms. The polyhedra are inter­connected by face‐ and edge‐sharing into layers. These layers are stacked by van der Waals forces between the protruding 2‐oxidobenzoate ligands.     

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.