Supramolecular chemistry

The article discusses molecular recognition and overviews the key concepts -storage and retrieval of chemical information by molecular structures, supramolecular reagents and catalysts, molecular transport, semiochemistry and self assembly. The prospects of controlling supramolecular architecture through engineered molecular recognition and design of ‘programmed systems’ controlled by molecular information are also discussed.     

Stereochemistry of reaction paths at carbonyl centres

Results of recent experimental and theoretical studies of nucleophilic addition to carbonyl groups are described. The reaction paths found by different methods for different nucleophiles show some striking similarities that appear to be characteristic for the reaction type.     

Molecular Ionics of Anion Receptor Molecules: A Microcalorimetric Study

The coordination of divalent and monovalent inorganic anions to synthetic polyammonium receptors is investigated in aqueous solution around neutral pH by titration calorimetry and NMR spectroscopy. High-affinity 1:1 complexes are formed by a pyrrole type cryptand (1) with sulfate and phosphate, characterized by association constants of almost 107 M^-1. Affinities close to 105 M^-1 are found for polyazacryptands (3 and 4) exhibiting F^-/Cl^- selectivity. The binding affinities and the anion selectivities are mainly caused by the charges of ligands and anions, which is discussed on the basis of simple calculations of the electrostatic contribution to the anion/receptor interactions. The binding of all investigated anions is exothermic at 298.2 K. The contribution of the large negative ΔH values to the free energy of anion binding of the pyrrole type ligand is partially compensated by marked negative ΔS values. These unfavorable entropic contributions are attributed to the additional inclusion of water molecules in the anion/receptor complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phase transfer of metal cations by induced dynamic carrier agents: biphasic extraction based on dynamic covalent chemistry

In contrast to the classical method where a single molecule is designed to extract metal cations under specific conditions, dynamic covalent chemistry provides an approach based on the implementation of an adaptive dynamic covalent library for inducing the generation of the extractant species. This approach has been applied to the liquid–liquid extraction of copper(ii) nitrate based on a dynamic library of acylhydrazones constituents that self-build and distribute through the interface of a biphasic system. The addition of copper(ii) cations to this library triggers a modification of its composition and the up-regulation of the ligand molecules driven by coordination to the metal cations. Among these, one species has proven to be sufficiently lipophilic to play the role of carrier agent and its formation by component exchange enables the partial extraction of the copper(ii). The study of different pathways to generate the dynamic covalent library demonstrates the complete reversibility and the adaptability of the system. The detailed analytical investigation of the system provides a means to assess the mechanism of the dynamic extraction process.

Phase transfer of Cu(ii) cations is achieved by component exchange in a dynamic covalent library of acylhydrazone ligands. B1/B2 component exchange leads to the generation of a lipophilic carrier agent that extracts Cu(ii) into chloroform.     

The electronic structure of bicyclo [2.1.1] hexane

Non empirical SCF-LCAO-MO calculations have been performed on bicyclo [2.1.1] hexane using a molecule optimized minimal basis set of gaussian functions. The electronic structure, the nature of the molecular orbitals and of the bonds are analyzed. The most notable results lie in the strong interaction between the two bridgehead sites and between two of the CH bonds of the methylene bridges. Interactions between fragment orbitals are considered. The relations with the molecular properties are discussed, especially with respect to molecular strain.

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Zusammenfassung Nichtempirische SCF-LCAO-MO-Rechnungen wurden für das Bicyclo [2.1.1]-Hexan durchgeführt, wobei ein minimaler am Äthylen optimierter Basissatz von Gaußfunktionen verwendet wurde. Die Elektronenstruktur sowie die Art der Molekülorbitale und der Bindungen wird untersucht. Als bemerkenswerte Resultate erscheinen die starke Wechselwirkung zwischen den beiden Brückenkopf-Gruppen sowie zwischen den beiden CH-Bindungen der Methylenbrücken. Die Wechselwirkungen zwischen den Orbitalen von Molekülbruchstücken werden untersucht. Die Beziehungen zu den molekularen Eigenschaften werden diskutiert, insbesondere im Hinblick auf molekulare Ringspannung.

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Résumé Une étude théorique ab initia SCF-LCAO-MO du bicyclo [2.1.1] hexane a été effectuée en utilisant une base minimale de fonctions gaussiennes optimisée sur une molécule. La structure électronique, la nature des orbitales moléculaires et des liaisons ont été analysées. Le résultat le plus marquant est l'existence d'une forte interaction entre les deux sites en tête de pont et aussi entre deux des liaisons C-H des ponts méthylène. Par ailleurs on peut mettre en évidence des interactions entre «orbitales de fragments». Les relations entre structure électronique et propriétés moléculaires (spécialement la tension de cycle) sont discutées.

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Equipe de Recherche Associée au C.N.R.S. N 265.     

Synthesis and structures of zirconium amide-iodide complexes

Zirconium amide-iodide complexes were synthesized for possible use as chemical vapor deposition precursors to zirconium nitride films. The series of six complexes Zr(NR(2))(4-n)I(n)(R = Me or Et; n = 1-3) was prepared by reacting ZrI(4) and Zr(NR(2))(4) in hot toluene. X-ray crystallographic analyses were performed for Zr(NMe(2))(3)I, Zr(NEt(2))(2)I(2), and Zr(NEt(2))I(3). In the solid state, Zr(NMe(2))(3)I and Zr(NEt(2))(2)I(2) are the discrete dimers [Zr(NMe(2))(2)I(mu-NMe(2))](2) and [Zr(NEt(2))(2)I(mu-I)](2), and Zr(NEt(2))I(3) is the polymer of dimers ([Zr(NEt(2))I(2)(mu-I)](2))(n). In solution, Zr(NEt(2))(3)I is proposed to be monomeric on the basis of NMR data and a molecular weight determination. The complex Zr(NEt(2))(3)I is the most promising precursor candidate because of its physical properties.