Synthesis and crystal structure of 1,3,5-tris [4-(phenylethynyl)phenyl]benzene

The crystal structure of 1,3,5-tris[4-(phenylethynyl)phenyl]benzene (1) has been investigated. Compound1 represents a model of the repeating unit of the most typical polyphenylene, which contains 1,3,5-trisubstituted benzene rings (chain centers) and acetylenic groups (complex-forming and cross-linking centers) in the main chain. The acetylene groups of neighboring molecules have a tendency to close mutual arrangement, which is favorable for their topochemical interaction. However, the relative conformational rigidity of molecules1 restricts not only the possibility of the optimal adjustment of the reactive sites of neighboring molecules to one another, but also hampers the close packing of molecules in the crystal, which contains channels filled by the solvent molecules (chloroform).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1986–1992, November, 1994.The work was carried out with the financial support of the International Science Foundation and the American Crystallographic Association.     

Heterometallic zirconocene(iii) aluminum hydride complex (Cp2ZrH)2HAlCl2·C4H8O2·C6H6

The heterometallic zirconocene(iii) aluminum hydride complex (Cp₂ZrH)₂HAlCl₂·C₄H₈O₂·C₆H₆ was synthesized by reduction of Cp₂ZrCl₂ with lithium aluminum hydride in the presence of Cp₂TiBH₄ and 1,4-dioxane, and its structure was established by X-ray diffraction analysis.     

Solvates of Indomethacin

Indomethacin is known to exhibit polymorphism and solvates, the different forms obtained do not exhibit the same solubility and their bioavailabilities are different. It is of a prime importance to identify the various polymorphic and solvated forms. This study was carried out by: DSC (different scanning calorimetry), TG (thermogravimetric analysis), X-ray diffraction and thermomicroscopy. Seven solvates, with acetone, benzene, dichloromethane, tetrahydrofurane, propanol, chloroform and diethylether, were isolated and studied. Their formulae have been determined by thermogravimetric analysis and their X-ray patterns on powder are presented, by DSC their behaviour after desolvation is recorded, the temperature and the enthalpy of fusion are measured and by this way the form obtained is deduced. This revised version was published online in July 2006 with corrections to the Cover Date.     

Properties of 8-Cyano-5-phenyl-7-trifluoromethyl-2,3-dihydroimidazo[1,2-a]pyridines

The alkylation, acylation, halogenation, nitration, oxidation, and hydrolysis reactions of 8-cyano-5-phenyl-7-trifluoromethyl-2,3-dihydroimidazo[1,2-a]pyridine have been studied. It was found that the 6-halo derivatives add alcohol to give covalent solvates. X-ray analysis has been carried out on one of the solvates (6-chloro-8-cyano-7-ethoxy-5-phenyl-7-trifluoromethyl-1,2,3,7-tetrahydroimidazo[1,2-a]pyridine) as well as on 8-cyano-5-phenyl-7-trifluoromethyl-2,3-dihydroimidazo[1,2-a]pyridine trifluoroacetate.     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Caracterisation par analyse calorimetrique differentielle des complexes entre LiAlH4 et les ethers-couronnes 12-C-4, 15-C-5, dicyclohexano-18-C-6

The thermal behaviour of complexes [Li⁺-EC](AlH₄)^– withEC=12-C-4, 15-C-5, DC 18-C-6 (cis-anti-cis andcis-syn-cis isomers) was investigated by Differential Scanning Calorimetry (DSC). These complexes were prepared as solids from benzene solutions. Pure EC and several solvated species [Li⁺-EC](AlH₄)^–·nC₆H₆ (EC=15-C-5, DC 18-C-6syn) were also studied. DSC has revealed various phenomena. Solid-solid transitions were observed before melting for [Li⁺-EC](AlH₄)^– withEC=12-C-4 and 15-C-5. They are probably explained by small molecular modifications strongly dependent on the thermal history of the sample. A glass-transition was found for the pure crown-ether DC 18-C-6anti, the complex [Li⁺-EC](A1H₄)^– withEC=DC-18-C-6anti and the two solvates mentioned above.

     

Stoichiometry,Association Constant,and Solvation Model of Chiral Hydroxyfuranones in the Presence of Pirkle's Alcohols

ABSTRACT

(S)-(+)-Dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone, (R)-(-)-dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone, (S)-(-)-dihydro-4-hydroxy-2(3H)-furanone, and (S)-(-)-5-hydroxymethyl-2(5H)-furanone in the presence of pure enantiomers of 2,2,2-trifluoro-1-(9-anthryl)ethanol were studied by ¹H NMR in deuterated chloroform solutions. Experimental Job's plots suggest that the resulting solvates are formed with one molecule of solute and one of the chiral solvating agent. From the magnitude of the association constant determined for (S)-(+)-dihydro-3-hydroxy-4,4-dimethyl-2(3H)-furanone in the presence of (R)-(-)-2,2,2-trifluoro-1-(9-anthryl)ethanol (1.26 ± 0.09 M^?1), it is inferred that the solvate is weak and cannot be isolated at 298 K. The correlation between the magnitude of induced chemical shifts, NOESY maps, and the known configuration of solutes and chiral solvating agents suggests that intermolecular hydroxyl-hydroxyl interaction is the primary interaction. Accordingly, the secondary interaction might occur between benzylic-hydrogen of the chiral solvating agent and the carbonyl- or furan ring-oxygen atoms of the solute.     

Diverse Modes of Solvent Inclusion in Crystalline Pseudopolymorphs of the Anthelmintic Drug Niclosamide

Single crystal X-ray structures of solvated forms of theanthelmintic drug Niclosamide reveal distinctly differentmodes of inclusion for different solvents. These modes are,respectively, cavity occupation by water molecules in 1 : 1niclosamide.H₂O, channel occupation by tetrahydrofuranmolecules in 1 : 1 niclosamide.THF, and intercalation bytetraethylene glycol molecules in 2 : 1 niclosamide.TEG. Inall three compounds the host drug molecule adopts the same,nearly planar conformation, which is maintained by anintramolecular N-H.O hydrogen bond. Host-guest recognitioninvariably involves hydrogen bonding between the drughydroxyl group and an oxygen acceptor atom of the solventmolecule. The observed modes of solvent inclusion can bereconciled with the behaviour of the crystals on heating.     

Towards prediction of stoichiometry in crystalline multicomponent complexes

We report on the crystal structure of urea (U) with acetic acid (A), its physical stability and its predictability using computational methods. The crystal structure of urea:acetic acid (U:A) shows hydrogen-bond ribbons and a 1:2 stoichiometry. Crystal structure prediction calculations are presented for two sets of U:A stoichiometries: 1:1 and 1:2. A 1:3 stoichiometry is also partially explored by means of a synthon approach. The calculated lattice energies, along with hydrogen-bond patterns, of crystal structures predicted with the three stoichiometries are presented and analysed to provide a rationalisation for the stoichiometry observed. Exploring stoichiometric diversity using computational methods provides a tool for the rationalisation of stoichiometry preferences in crystalline multicomponent systems and a first step towards their prediction.     

Thermal Analysis,Microcalorimetry and Combined Techniques for the Study of Pharmaceuticals

Modern thermal analysis, microcalorimetry and new emerging combined techniques which deliver calorimetric, microscopic and spectroscopic data offer a powerful analytical battery for the study of pharmaceuticals. These techniques are very useful in all steps of development of new drug products as well as methods for quality control in production. The characterization of raw materials enables to understand the relationships between polymorphs, solvates and hydrates and to choose the proper development of new drug products with very small amount of material in a very short time. Information on stability, purity is valuable for new entities as well as for marketed drug substances from different suppliers. Excipients which vary from single organic or inorganic entity to complexes matrixes or polymers need to be characterized and properly controlled. The thermodynamic phase-diagrams are the basis of the studies of drug-excipients interactions. They are very useful for the development of new delivery systems. A great number of new formulations need proper knowledge of the behaviour of the glass transition temperature of the components. Semi-liquid systems, interactions in aqueous media are also successfully studied by these techniques. This revised version was published online in August 2006 with corrections to the Cover Date.