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Crystal structures described as concomitant triclinic (I) and monoclinic (II) polymorphs of meso‐(E,E)‐1,1′‐[1,2‐bis(4‐chlorophenyl)ethane‐1,2‐diyl]bis(phenyldiazene) [Mohamed et al. (2016). Acta Cryst. C72, 57–62] have been re‐investigated. The published model for II was distorted due to forcing the symmetry of space group C2/c on an incomplete structure model. It is shown here to be a likely three‐component superposition of S,S and R,R enantiomers with a lesser amount of the meso form. A detailed analysis of how the improbable distortion in the published model aroused suspicion and the subsequent construction of undistorted chemically and crystallographically plausible alternatives having the symmetry of Cc and C2/c is presented. For the sake of completeness, an improved model for the triclinic P structure of the meso isomer I, revised to include a minor disorder component, is also given. [ABSTRACT FROM AUTHOR]

Nucleophilic aromatic substitution (SNAr) reactions are exploited to prepare poly(arylene sulfide)s (PAS's) via the reaction of bis‐thiolates and dibrominated pyromellitic diimide (PMDI) derivatives. Small‐molecule model studies reveal the reaction is well‐defined and proceeds in quantitative yield in practical times at room temperature. Variation in comonomer feed ratios allowed some control over target polymer molecular weights in the step polymerization, but control was likely limited by the relatively poor polymer solubility in the dipolar aprotic solvents typically employed to promote SNAr reactions. One substitution pattern produces a steric "pocket" around the PMDI units, inducing a peculiar solubility trend in halogenated solvents; that is, greatly reduced solubility in CHCl3 relative to CH2Cl2 and C2H2Cl4. One example small‐molecule readily dissolves in CHCl3 at room temperature, then rapidly grows poorly soluble crystals revealed by single‐crystal XRD to contain CHCl3 molecules in the steric pockets. Finally, the recently demonstrated depolymerization of phthalonitrile‐based PAS's via ipso substitution with monothiolates as chain scission agents yields quantitative molecular weight reduction to monomeric species from the polymers reported here. [ABSTRACT FROM AUTHOR]

Dehydroannulenes are alkyne‐rich macrocycles possessing rigid, planar, π‐conjugated backbones. Octadehydro[12]annulenes in particular are formally antiaromatic, and have been shown to possess stable reduced states with exploitable LUMO energies. However, very few examples of this type of annulene have been structurally characterized, and there is little information on the stability of these antiaromatic molecules in solution or in the solid state. We have synthesized a range of substituted octadehydro[12]annulenes, and characterized their optical and redox properties. Contrary to prior reports, dehydro[12]annulenes with overlapping π‐surfaces are reasonably stable both in solution and thin films, suggesting potential use in practical applications. [ABSTRACT FROM AUTHOR]

The β‐diketone scaffold is a commonly used synthetic intermediate, and is a functional group found in natural products such as curcuminoids. This core structure can also act as a chelating ligand for a variety of metals. In order to assess the potential of this scaffold for medicinal inorganic chemistry, seven different κ2‐O,O'‐chelating ligands were used to construct Ru(II) complexes with polypyridyl co‐ligands, and their biological activity was evaluated. The complexes demonstrated promising structure‐dependent cytotoxicity. Three complexes maintained high activity in a tumor spheroid model, and all complexes demonstrated low in vivo toxicity in a zebrafish model. From this series, the best compound exhibited a ∼30‐fold window between cytotoxicity in a 3‐D tumor spheroid model and potential in vivo toxicity. These results suggest that κ2‐O,O'‐ligands can be incorporated into Ru(II)‐polypyridyl complexes to create favorable candidates for future drug development. [ABSTRACT FROM AUTHOR]

Addition of the potassium dichalcogenidodiphenylphosphinate salts, KE2PPh2 (E=S, Se), to either the THF solvate of vanadium(III) chloride or unsolvated chromium(III) chloride results in rapid ligand substitution and the formation of a series of closely‐related trivalent, neutral mononuclear complexes, M(E2PPh2)3 (M=V, Cr; E=S, Se), isolated in modest to good yield. The metal dichalcogenidophosphinate complexes reported herein were characterized by IR, UV‐vis, and 1H NMR spectroscopies, and their solid‐state molecular structures were determined by single‐crystal X‐ray crystallography. Importantly, the comparative analysis includes the structural and spectroscopic studies of two rare V(III) dithio‐ and diseleno‐phosphinate VE6 cores, as well as, two previously known CrE6 analogues. In the solid‐state the title complexes exhibit trigonal distortion from octahedral with torsion angles ranging from 43(2) to 50.3(6)° and structural parameters consistent with ligation of progressively 'softer' chalcogen‐donors. [ABSTRACT FROM AUTHOR]

The ever‐expanding need for renewable energy can be addressed in part by photocatalytic CO2 reduction to give fuels via an artificial photosynthetic process driven by sunlight. A series of rhenium photocatalysts are evaluated in the photocatalytic CO2 reduction reaction and via photophysical, electrochemical, and computational studies. The impact of various electron withdrawing substituents on the aryl group of the pyNHC‐aryl ligand along with the impact of extending conjugation along the backbone of the ligand is analyzed. A strong correlation between excited‐state lifetimes, photocatalytic rates, and computationally determined dissociation energy of the labile ligand of these complexes is observed. Additionally, computed orbital analysis provides an added understanding, which allows for prediction of the potential impact of an electron withdrawing substituent on photocatalysis. [ABSTRACT FROM AUTHOR]

The rate of singlet fission, the process of generating two triplet excitons with photoexcitation of one singlet exciton, depends on a combination of singlet/triplet energy balance and intermolecular coupling. Here, we perform carboxylic acid functionalization of anthradithiophene (ADT) derivatives that results in hydrogen bonds that drive molecular orientation and strong electronic coupling of polycrystalline ADT thin films, leading to ultrafast singlet fission without significant enthalpic driving force. ADT with a single carboxylic acid group exhibits weak intermolecular coupling and slow and inefficient singlet fission, much like the parent ADT, and substitution of different alkylsilyl solubilizing groups has little effect. However, the addition of two carboxylic acid groups on either end of the long axis favors significant coupling and crystallinity in as‐deposited thin films that increase the effective singlet fission rate by roughly three orders of magnitude. The properties of the triplet pair, particularly its propensity to form long‐lived independent triplets, are also influenced by the degree of long‐range intermolecular coupling. The enhancement of intermolecular coupling specific to singlet fission using the ubiquitous cyclic hydrogen bonding motif could impact triplet pair utilization schemes in a variety of contexts. [ABSTRACT FROM AUTHOR]

Threefold twinning in 1‐{(R)‐1‐[(3‐oxo‐2‐isoindolinoyl)methyl]‐2‐propenyl}‐5‐methyl‐2,3‐indolinedione, C21H16N2O4, has been reported recently [Trost et al. (2020). Org. Lett.22, 2584–2589] but the twin characterization was not published. This twinning presents several interesting features. The crystal structure is monoclinic, but its lattice is metrically strongly pseudo‐orthorhombic and underpins a strongly pseudo‐hexagonal sublattice. Several possible twin laws are compatible with these metric specializations, among which the one found experimentally corresponds to a trichromatic point group. Twinning is by reticular pseudo‐merohedry with twin index 2 and zero obliquity but a non‐zero twin misfit. The twin lattice coincides with the pseudo‐hexagonal sublattice of the individual domain, which justifies the adoption of the unconventional setting B21 of the space group. [ABSTRACT FROM AUTHOR]

The solid-state properties of 2-[(2,6-dichlorophenyl)amino]-benzaldehyde ( DCABA) were investigated. Unlike its precursor diclofenac acid, for which three polymorphs are currently known, only one crystalline form of DCABA was found. It was further characterized by other spectroscopic and spectrometric methods including IR, Raman, and UV-vis spectroscopy and powder X-ray diffraction ( PXRD). The thermal behavior of the crystalline form was studied by differential scanning calorimetry ( DSC). Theoretical studies, including Hirshfeld surface analysis and conformational energy searches, were performed to provide insight into the factors contributing to the stability of the crystal and to assess the possibility of additional polymorphs. The full characterization of this compound can help fast and accurate identification of DCABA both in dosage forms and in the environment. [ABSTRACT FROM AUTHOR]

Ruthenium complexes capable of light-triggered cytotoxicity are appealing potential prodrugs for photodynamic therapy (PDT) and photoactivated chemotherapy (PACT). Two groups of (polypyridyl)RuII complexes with 2-(2-pyridyl)benzazole ligands were synthesized and investigated for their photochemical properties and anticancer activity to compare strained and unstrained systems that are likely to have different biological mechanisms of action. The structure-activity relationship was focused on the benzazole-core bioisosterism and replacement of coligands in RuII complexes. Strained compounds rapidly ejected the 2-(2-pyridyl)benzazole ligand after light irradiation, and possessed strong toxicity in the HL-60 cell line both under dark and light conditions. In contrast, unstrained RuII complexes were nontoxic in the absence of light, induced cytotoxicity at nanomolar concentrations after light irradiation, and were capable of light-induced DNA damage. The 90-220-fold difference in light and dark IC50 values provides a large potential therapeutic window to allow for selective targeting of cells by exposure to light. [ABSTRACT FROM AUTHOR]

Four cyclopentenone-containing ansamycin polyketides (mccrearamycins A-D), and six new geldanamycins (Gdms B-G, including new linear and mycothiol conjugates), were characterized as metabolites of Streptomyces sp. AD-23-14 isolated from the Rock Creek underground coal mine acid drainage site. Biomimetic chemical conversion studies using both simple synthetic models and Gdm D confirmed that the mccrearamycin cyclopentenone derives from benzilic acid rearrangement of 19-hydroxy Gdm, and thereby provides a new synthetic derivatization strategy and implicates a potential unique biocatalyst in mccrearamycin cyclopentenone formation. In addition to standard Hsp90α binding and cell line cytotoxicity assays, this study also highlights the first assessment of Hsp90α modulators in a new axolotl embryo tail regeneration (ETR) assay as a potential new whole animal assay for Hsp90 modulator discovery. [ABSTRACT FROM AUTHOR]

Anthradithiophene chromophores are found in many current high-performance organic semiconductors, even though these materials are typically synthesized as an inseparable mixture of syn and anti isomers. Recent syntheses of pure syn anthradithiophenes have shown no improvement in performance for the more homogeneous system, but similar studies on the pure anti isomer have not been reported. In this work, a simple protocol is described to prepare the pure anti isomer of fluorinated, functionalized anthradithiophenes, and perform detailed analysis of the intermolecular interactions in the crystal that yield increased density and closer chromophore contacts. Studies of the charge-transport properties of these pure isomers, compared to the isomeric mixtures, suggest that the benefit of isomer purity is not consistent; in the syn case, there was minimal difference between the pure isomer and the mixture, while for the anti isomer mobility improved nearly twofold. Analysis of disorder in the crystals suggests a reason for this difference in performance. [ABSTRACT FROM AUTHOR]

The only crystals that could be grown from racemic solutions of the PF6− salt of the resolvable cation [Ru(2,9-dimethyl-1,10-phenanthroline)2(dipyrido[3,2- d:2′,3′- f]quinoxaline)]2+ have translational symmetry only (space group P1), contain nine independent sets of ions, and include numerous independent solvent molecules (11 acetone, one diethyl ether and possibly several water molecules). Layers of hydrophobic cations alternate with layers containing most of the anions and solvent molecules. All nine cations have the same basic conformation, which is distorted by the presence of the methyl substituents on the two 1,10-phenanthroline ligands. Four pairs of enantiomeric cations within a layer are related by approximate inversion centers; the ninth cation, which shows no sign of disorder, makes the layer chiral. Within the cation layers stripes parallel to [110] of six cations alternate with stripes of three; the local symmetry and the cation orientations are different in the two stripes. These stripes are reflected in the organization of the anion/solvent layer. The ca 80:20 inversion twinning found indicates that enantiomeric preference is transmitted less perfectly across the anion/solvent layer than within the cation layer. The structure is exceptional in having nine independent formula units and an unbalanced set (ratio 4:5) of resolvable enantiomers. The difficulty in growing crystals of this material is consistent with its structural complexity. [ABSTRACT FROM AUTHOR]

Recognition and regulation of G-quadruplex nucleic acid structures is an important goal for the development of chemical tools and medicinal agents. The addition of a bromo-substituent to the dipyridylphenazine (dppz) ligands in the photophysical 'light switch', [Ru(bpy)2dppz]2+, and the photochemical 'light switch', [Ru(bpy)2dmdppz]2+, creates compounds with increased selectivity for an intermolecular parallel G-quadruplex and the mixed-hybrid G-quadruplex, respectively. When [Ru(bpy)2dppz-Br]2+ and [Ru(bpy)2dmdppz-Br]2+ are incubated with the G-quadruplexes, they have a stabilizing effect on the DNA structures. Activation of [Ru(bpy)2dmdppz-Br]2+ with light results in covalent adduct formation with the DNA. These complexes demonstrate that subtle chemical modifications of RuII complexes can alter G-quadruplex selectivity, and could be useful for the rational design of in vivo G-quadruplex probes. [ABSTRACT FROM AUTHOR]

Dimers of 2-substituted N,N′-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer CC bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2, yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2) dissociation and of D2-to-A electron transfer, D2 reacts with A to form D+ and A− by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D+/0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. −1.9 V vs. FeCp2+/0) (Cp=cyclopentadienyl) due to cancelation of trends in the D+/0 potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed. [ABSTRACT FROM AUTHOR]

Tri-isopropylsilylethynyl (TIPS)-functionalized polycyclic aromatic hydrocarbon (PAH) molecules incorporate structural components of graphene nanoribbons and represent a family of model molecules that form organic crystal semiconductors for electronic devices. Here, we report a series of TIPS-functionalized PAHs and discuss their electronic properties and crystal packing features. We observe that these soluble compounds easily form one-dimensional (1 D) packing arrangements and allow a direct evolution of the π stacking by varying the geometric shape. We find that the aspect ratio between length and width plays an important role on crystal packing. Our result indicates that when the PAH molecules have zigzag edges, these can provide enough volume for the molecules to rotate and reorient, alleviating the unfavorable electrostatic interactions found in perfectly cofacial π-π stacking. Density functional theory calculations were carried out to provide insights into how the molecular geometric shape influences the electronic structure and transport properties. The calculations indicate that, among the compounds studied here, 'brick-layer' stacks provide the highest hole mobility. [ABSTRACT FROM AUTHOR]

Crystals of 2-chloro-benzo-1,3,2-dithiarsole have a strongly modulated structure that can be solved and refined with relative ease in a P, Z′ = 17 approximate supercell but that is better described as incommensurate. Two conventional refinements (different superstructure approximations that differ in the placement of their crystallographic inversion centers) and a (3 + 1)-dimensional superspace refinement are all nearly equally successful, at least as measured by the usual agreement factors; the data integration, however, shows that the incommensurate description is preferable. The overall packing is determined by the stacking of the aromatic rings and probably by the segregation of As and Cl atoms to give short As...Cl contacts. A refinement of the average ( Z′ = 1) structure shows that there are two basic orientations of the C6S2 plane, but that those orientations must be correlated in several directions to avoid impossibly short intermolecular contacts. Along the modulation vector q the orientation of the C6S2 plane varies smoothly, but q is not a direction in which the molecules are in contact. Along the directions in which the molecules are in contact the orientation of the C6S2 plane alternates; there are also positional shifts. The single modulation q relieves packing problems in several different directions well enough that crystals that diffract well can be grown. [ABSTRACT FROM AUTHOR]

Novel ninhydrin-creatinine heterocyclic condensation products ( 3-5) were synthesized under different solvent conditions. The compound 2-(2-amino-1-methyl-4-oxo-4,5-dihydro-1 H-imidazol-5-yl)-2-hydroxy-1 H-ind-ene-1,3(2 H)-dione ( 3) was formed by reacting ninhydrin ( 1) with creatinine ( 2) in the presence of sodium acetate in acetic acid. The same reactants afforded the zwitterionic compound 4 when the reaction was carried out in water, and a novel oxadiazine ring system (product 5) was generated when benzene was used as solvent. [ABSTRACT FROM AUTHOR]

A sequence of four phases has been found for an acetonitrile-solvated co-crystal with 15-crown-5 of the nickel complex [acetonitrilediaqua-κ1 O-nitrato-κ2 O-nitratonickel(II)]. The structure could be determined at intervals of ca 10 K in the range 90-273 K because crystals remain single through the three transitions. In phase (I) ( T≥ ca 240 K; P21/ m, Z′ = ½), there is extensive disorder, which is mostly resolved in phase (III) ( ca 230-145 K; P21/ c, Z′ = 1). Phase (IV) ( ca 145-90 K, and probably below; P, Z′ = 2) is ordered. Phase (II) ( ca 238-232 K) is modulated, but the satellite reflections are too weak to allow the structure to be determined within its stability range by standard methods. Most crystals that were flash-cooled from room temperature to 90 K have a metastable P21, Z′ = 5 superstructure that (at least in a commensurate approximation) was identified as similar to the structure of phase (II) by comparison of reconstructed reciprocal-lattice slices and by analogy with the phase behavior of the very similar compound [Ni(H2O)6](NO3)2·(15-crown-5)·2H2O [Siegler et al. (2011). Acta Cryst. B 67, 486-498]. In the phase (II) structure slab-like regions that are like the disordered phase (I) structure alternate with regions of similar shape and size that are like the more ordered phase (III) structure. [ABSTRACT FROM AUTHOR]

In the range 308-90 K single crystals of [Ni(H2O)6](NO3)2·(15-crown-5)·2H2O continue to diffract well as they undergo three phase transitions. Structures have been determined at 28 different temperatures; data were collected at six more but could not be refined satisfactorily. The transitions identified structurally are in good agreement with those found by thermal analysis. Phase I (above ca 292 K; I2/ m, Z = 2, Z′ = ¼) is disordered because the 15-crown-5 molecule is located on a 2/ m site. Phase II ( ca 292-248 K; P21/ m, Z = 2, Z′ = ½) is less disordered. Phase III ( ca 248-208 K; B21, Z = 28, Z′ = 7 in a commensurate approximation) is modulated with some regions resembling phase II and the rest resembling the fully ordered phase IV ( P21/ c, Z = 4, Z′ = 1) that is stable below ca 208 K. The modulated structure could be determined well because crystals flash-cooled to 90 K usually retain the phase III structure. The unusual phase III may be a consequence of the differing thermal contraction of two types of alternating layers, one composed of neutral 15-crown-5 molecules and the other composed of the cations, anions and lattice water molecules, which form a hydrogen-bonded network. The two kinds of layers are linked by Oether...H2Oaxial-Ni hydrogen bonds. [ABSTRACT FROM AUTHOR]

The article provides the crystal structure of 5-hydroxy-5-methyl-2-pyridone grown from various solvents. The crystals are constantly trigonal which include 5-hydroxy-6-methyl-2-pyridone acetone 0.1887=solvate, 6-methyl-5-hydroxy-2-pyridone propan-2-ol 0.1667-solvate as well as the form from methanol, water, benzonitrile and benzyl alcohol. They have channels running at the c axis with disordered solvent molecules. The bond lengths and angles are within normal ranges and the molecules are flat.

The article focuses on the phase transition between 190 and 200 K in [Ni(H2O)6](NO3)2·(15-crown-5)·H2O. It states that differential scanning calorimetry (DSC) was conducted to examine the compound's thermal behavior while packings' rotatable overlays were made to compare the transition. Results show that structural changes expand over a wide range of temperature while the transition temperature ranges near the upper end.

Five structures of co-crystals grown from aqueous solutions equimolar in 15-crown-5 (or 15C5) and [ M(H2O)6](NO3) n, M = Al3+, Cr3+ and Pd2+, are reported. The hydrogen-bonding patterns in all are similar: metal complexes including the fragment trans-H2O- M-OH2 alternate with 15C5 molecules, to which they are hydrogen bonded, to form stacks. A literature survey shows that this hydrogen-bonding pattern is very common. In each of the two polymorphs of the compound [Al(H2O)6](NO3)3·15C5·4H2O there are two independent cations; one forms hydrogen bonds directly to the 15C5 molecules adjacent in the stack, while the other cation is hydrogen-bonded to two water molecules that act as spacers in the stack. These stacks are then crosslinked by hydrogen bonds formed by the three nitrate counterions and the three lattice water molecules. The hydrogen-bonded stacks in [Cr(H2O)5(NO3)](NO3)2·1.5(15C5)·H2O are discrete rather than infinite; each unit contains two Cr3+ complex cations and three 15C5 molecules. These units are again crosslinked by the uncoordinated nitrate ions and a lattice water molecule. In [Pd(H2O)2(NO3)2]·15C5 the infinite stacks are electrically neutral and are not crosslinked. In [Pd(H2O)2(NO3)2]·2(15C5)·2H2O·2HNO3 a discrete, uncharged unit containing one Pd complex and two 15C5 molecules is `capped off' at either end by a lattice water molecule and an included nitric acid molecule. In all five structures the infinite stacks or discrete units form an array that is at least approximately hexagonal. [ABSTRACT FROM AUTHOR]

Initial attempts to make {Ni(H2O)2(15-crown-5)](NO3)2, i.e. to insert the Ni2+ ion into the 15-crown-5 macrocycle, gave the mono-(two polymorphs) and dihydrate of a co-crystal of [Ni(H2O)6] (NO3)2 and 15-crown-5 (1,4,7,10,13-pentaoxacyclo- pentadecane = 15C5). Synthetic routes designed to restrict the water available to the Ni2+ cation gave three additional compounds, [Ni(H2O)6] (NO3)2-trans-[Ni(H2O)4(MeOH)2]- (NO3)2·2(15C5), cis-[Ni(H2O)4(NO3)2]-trans-[Ni(H2O)4- (NO3)2]·2(15C5) and [Ni(H2O)2(MeCN)(NO3)2]·15C5 MeCN. All five compounds contain Ni2+ ions with two trans aqua ligands. In all six structures these aqua ligands make hydrogen bonds to the 15C5 molecules to form stacks in which the Ni complexes and 15C5 molecules alternate. The structures are surprisingly complicated: all are co-crystals, some are also solvates, and most have Z' > 1. The target compound was finally prepared by heating pale green crystals of [Ni(H2O)6](NO3)2·15C5·2H2O to over 350 K and then cooling the resulting mixture of yellow crystals and solution to room temperature. Formation of the target compound seems to be favored at higher temperatures by a positive ΔrxnS° and an increased rate of ligand exchange. [ABSTRACT FROM AUTHOR]

A 1:1 co-crystal of rac- trans-1,2-C6H10(OH)2 and (C6H5)3PO has been found that is unusual because there are no strong interactions between the two kinds of molecules, which are segregated into layers. Furthermore, neither pure rac-1,2-cyclohexanediol (CHD) nor pure triphenylphosphine oxide (TPPO) has any obvious packing problem that would make the formation of inclusion complexes likely. The TPPO layers are very much like those found in two of the four known polymorphs of pure TPPO. The hydrogen-bonded ribbons of CHD are similar to those found in other vic-diol crystals. The co-crystals are triclinic (space group P ), but the deviations from monoclinic symmetry (space group C2/ c) are small. The magnitudes of those deviations depend on the solvent from which the crystal is grown; the deviations are largest for crystals grown from acetone, smallest for crystals grown from toluene, and intermediate for crystals grown from ethanol. The deviations arise from incomplete enantiomeric disorder of the R, R and S, S diols; this disorder is not required by symmetry in either space group, but occupancy factors are nearly 0.50 when the structure is refined as monoclinic. When the structure is refined as triclinic the deviations of the occupancy factors from 0.50 mirror the deviations from monoclinic symmetry because information about the partial R, R/ S, S ordering is transmitted from one diol layer to the next through the very pseudosymmetric TPPO layer. Analyses suggest individual CHD layers are at least mostly ordered. The degree of order seems to be established at the time the crystal is grown and is unlikely to change with heating or cooling. Thermal data suggest the existence of the co-crystal is a consequence of kinetic rather than thermodynamic factors. [ABSTRACT FROM AUTHOR]

The phases of 1,2,3,4-tetrahydro-2,3-naphthalenediol (or 2,3-tetralindiol) and of 1,2-cyclohexanediol have been investigated. The structure of a very stable 1:1 compound (or co-crystal) of the cis and trans isomers of 2,3-tetralindiol, the existence of which has been known for nearly a century, has finally been determined. No evidence of any analogous compound between the cis and trans isomers of 1,2-cyclohexanediol has been found. The formation of solid-state compounds of stereoisomers is rare; it probably occurs only if the crystal packing of at least one of the isomers is unfavorable, e.g. if at least one of the melting points is lower than expected. Compound formation is usually unlikely because of the difficulty of simultaneously optimizing the translational spacings for both isomers, but that packing problem is avoided in the cis/ trans compound of 2,3-tetralindiol because the two isomers are in very similar environments. In the structures of the individual 2,3-tetralindiol isomers there are clear conflicts between the competing packing requirements of the 1,2-diol moiety and the aromatic ring system; these conflicts are resolved better in the co-crystal than in the structures of the individual isomers. [ABSTRACT FROM AUTHOR]

The structures of [ M(H2O)2(15-crown-5)](NO3)2, M = Cu, Zn, Mg and Co, and 15-crown-5 = 1,4,7,10,13-pentaoxacyclopentadecane, have been redetermined at 294 and 90 K. The four structures, and a second form of the Cu structure, have been reported in the literature, but are all incorrect in some significant way. The structures, which all have at least two independent formula units ( i.e. Z′≥ 2), are related; each water ligand is hydrogen-bonded to two nitrate anions, while each nitrate anion is hydrogen bonded to the water ligands of two cations. In the tetragonal Co structure the hydrogen-bond pattern is three-dimensional; in the monoclinic Cu, Zn and Mg structures the hydrogen-bond patterns are two-dimensional. In the isostructural Zn and Mg structures Z′ = 3, while in the Cu structure Z′ = 5. The Cu, Zn and Mg structures are modulated variants of a basic structure, which was reported for Cu but which probably does not exist. The conformations of the 11 independent cations are remarkably similar; they all have approximate twofold symmetry and so exist as conformational enantiomers. The most important modulation is imperfect enantiomeric alternation of the cations along the longest cell axis; the independent cations are related by very good pseudotranslation and pseudoinversion operations. The diffraction patterns for all four structures have classes of weak, even very weak, reflections. [ABSTRACT FROM AUTHOR]

The structure of highly twinned pinacol (2,3-dimethyl-2,3-butanediol) monohydrate, the existence of which has been known since 1922, has been determined, and the structures of anhydrous pinacol and its two other known hydrates have been reinvestigated. All the phases are unusual. The anhydrous phase [Jeffrey & Robbins (1978). Acta Cryst. B 34, 3817–3820] is exceptional among molecular crystals in having molecules located on three different symmetry sites (1, and 2). A hexagonal form of pinacol originally described as a second polymorph [Dahlqvist & Sillanpää (2000). J. Mol. Struct. 524, 141–149] has been shown to be a solvate of uncertain composition that is very loosely packed. Pinacol hexahydrate, which was originally reported as tetragonal and highly disordered [Kim & Jeffrey (1970). J. Chem. Phys. 53, 3610–3615], appears to be described better as having an orthorhombic structure that is both disordered and twinned; the diffraction pattern at 90 K shows structured diffuse scattering that suggests short-range correlations of disordered molecules. The occurrence of this unusual set of structures is attributed to the combination of the hydrogen-bonding requirements of the pinacol molecule with its small size and limited conformational flexibility. [ABSTRACT FROM AUTHOR]

The structure of N′ -cyan o-N,N-diisopropylguanidine, a push- pull nitrile that includes the H2N - C=N - CN fragment, has been determined. Although the number of molecules in the asymmetric unit is exceptionally high (Z′' = 10), there were no special crystallographic difficulties associated with data collection, structure solution or structure refinement because the individual molecules are small (12 non-H atoms) and because there is no important crystallographic pseudosym- metry. A complete set of N - …N bonds is formed. Pairs of molecules form dimer's, which associate to form ribbons that twist into a helix having five dimer's per turn. The helices lie parallel to [1011 and fit together with close contacts in three different directions perpendicular to that axis. The problems with optimizing so many different intermolecular contacts lead to a loosely packed structure. [ABSTRACT FROM AUTHOR]

Dimers of the partially fluorinated amphiphile 1-(perfluorobutyl)undecanoic acid, CF3(CF2)3(CH2)10COOH, crystallize in the same basic packing arrangement found for many n-alkyl carboxylic acids. The unit cell of the fluorinated compound, however, contains five independent molecules rather than the one found for most n-alkyl carboxylic acids including CH3(CH2)13COOH. The structures of the two C15 acids are compared. The structural modulations that lead to the large value of Z′ can be understood as resulting from the conflict between the necessity of filling space densely and uniformly and the tendency of unlike groups to be segregated spatially. The few other known structures of compounds with both (CF2)n and (CH2)m regions show evidence of the same conflict. [ABSTRACT FROM AUTHOR]

The substantially disordered structure of 2-biphenylol [Perrin et al. (1987). Acta Cryst. C43, 980-982; Kapon & Reisner (1988). Acta Cryst. C44, 2039] has been reinvestigated as a function of temperature. The structure was determined at 305, 294, 145 and 90 K; crystals were taken to the lowest temperature both rapidly and slowly (0.1 K min-1). The results of the previous room-temperature study were confirmed and no important structural change was found down to 90 K. Comparisons with structures known for other simple 2- and 2,2'-substituted biphenyl derivatives suggest that the molecular stacks found for 2-biphenylol are probable for related molecules. The disorder in 2-biphenylol allows the formation of some O-H···O bonds, but packing efficiency is a more important factor in this structure than is hydrogen bonding. [ABSTRACT FROM AUTHOR]

Flash-cooled crystals of the /222 form of concanavalin. A undergo a sharp non-destructive non-reversible phase transition upon warming to between 160 and 165 K. characterized by an anomalous increase in unit-cell volume, The expansion is anisotropic and primarily affects the p and c axes. Three sets of 1.7 Å X-ray diffraction data were collected from one crystal: immediately after flash-cooling (130 K), after slow warming to 170 K and after re-cooling to 130 K. Measurable changes in reflection width after the transition were apparent. Each data set was collected under very similar conditions (aside from temperature). Structures refined against each data set using a powerful phase-bias reduction algorithm indicate negligible rearrangement of the protein molecule and its first hydration shell. Further away from the protein surface, on the edge of the fully disordered solvent regions, a small number of more dramatic changes were apparent. Little is known about the behaviour of water confined within dimensionally restricted spaces, but solvent cavities and channels in protein crystals provide a rich source of reproducible nanoscale water assemblies. This paper presents information on the behaviour of water continued within protein cavities in relation to the physics of protein crystal annealing. [ABSTRACT FROM AUTHOR]

Investigates the supramolecular aggregation in 4,4'-bipyridin-1,1'-ium dichloride and 4,4'-bipyridin-1,1'-ium dinitrate. Crystal structure; Hydrogen bonds; Molecular interactions.

Crystals of 4-chloro-2'-tiphenylol grown at 263 K and studied at both 293 and 142 K are loosely packed and contain OH…O bonded tetramers composed of four crystallographically independent molecules (Z' = 4). Approximate symmetry relationships between independent molecules are apparent in many, perhaps even most, structures with Z' > 1, but are not obvious in this structure. The inefficient crystal packing, the surprisingly large value of Z' and the absence of pseudosymmetry reflect the difficulty of finding a dense molecular arrangement that also allows for hydrogen-bond formation. Impediments to good packing are the steric congestion around the ortho hydroxyl groups and the difficulty in filling space with significantly twisted biphenyl fragments. The packing arrangement adopted is strongly reminiscent of the structure type found for eight simple 44'-biphenyl derivatives, but one of the four independent 4'-chloro-2-biphenylol molecules has an orientation that is significantly different from the orientations of the other three and that does not fit the 4,4'-XPhPhY pattern. It is suggested that molecules that crystallize with Z'> 1 are good candidates for solid-state compound formation. [ABSTRACT FROM AUTHOR]

Reports findings of a study where structures of two derivatives of the curved fluoradene ring system (C[sub 19]H[sub 12]) were determined. Finding that both have phases that are pseydosymmetric; Characterization of some of the atomic ellipsoids as very large and eccentric.

Details a simple general method to quantify spatial variations in scalar statistics. Use of the R tensor to represent the local average residual as a function of diffraction geometry; Differences in the effective R indices for individual reflections or groups of reflections to help steer refinement strategy and assess the final structure.

Reports on crystals of pure laboratory-grown uric acid dihydrate which are monoclinic. Exhibition of pseudo-orthorhombic twinning with refined twin fractions; Existence of a disorder about a noncrystallographic twofold; Epitaxy of uric acid dihydrate with its anhydrous counterpart.