Recent Publications

| 2017 | 2016 | 2015 | 2014 | 2013 | 2012 | 2011 | 2010 | more >

  1. Title: Effect of hydrophobic nanopatches within an ionic surface on the structure of liquids

    Author(s): Youngs T.G.A., Hardacre C.,

    Physical Chemistry Chemical Physics, 13, No. 2, pp. 582-585 (2011)

    Abstract


    The structures of liquid water and isopropanol have been studied as a function of the size of a hydrophobic patch present in a model hydrophilic surface via molecular dynamics simulations. A significant anisotropy extending into the first few solvent layers is found over the patch which suggests implications for many real-world systems in which nanoscale heterogeneity is found.

  2. Title: Dispersion interactions in room-temperature ionic liquids: Results from a non-empirical density functional

    Author(s): Kohanoff J.J., Pinilla C., Youngs T.G.A., Artacho E., Soler J.M

    Journal of Chemical Physics, 135, pp. 154505- (2011)

    Abstract


  3. Title: Aten-An Application for the Creation, Editing, and Visualization of Coordinates for Glasses, Liquids, Crystals, and Molecules

    Author(s): Youngs T.G.A.,

    Journal of Computational Chemistry, 31, No. 3, pp. 639-648 (2010)

    doi: 10.1002/jcc.21359
    Abstract



    Aten is a tool for Linux, Mac, and Windows platforms to ease the creation, editing, and visualization of coordinates for use in, for example, molecular dynamics simulations. The code handles gas-phase molecules in addition to crystals, surfaces, and liquids, providing standard tools to edit "by the atom" along with specific "by the box" methods suited to periodic systems, including full crystallographic spacegroup packing definitions. Visualization of systems encompasses the standard drawing styles and may be mixed with an arbitrary number of other basic objects, such as arrows and geometric objects allowing creation of scenes involving vector fields, coarse-grained particles, etc. Standard molecular mechanics forcefields can be read in, edited, applied to molecules using the built-in chemical typing language, and subsequently used to calculate energies and forces, minimize energies with respect to coordinates, decompose energies into contribution by molecule type, etc. Monte Carlo methods are available with which to generate random configurations of N-component systems, or solvate around molecules or in specific regions within existing configurations. Supported file formats are governed by user-defined "filters," which provide flexibility of input/output as well as the ability to define custom or extended formats of traditional files. Forcefield descriptions for loaded systems can be output and formatted for use as input to common codes. All features can be accessed by a comprehensive GUI and scripting language based on the C syntax. (C) 2009 Wiley Periodicals, Inc. J Comput Chem 31: 639-648, 2010

  4. Title: Solid and liquid charge-transfer complex formation between 1-methylnaphthalene and 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

    Author(s): Hardacre C., Holbrey J.D., Mullan C.L., Nieuwenhuyzen M., Youngs T.G.A., Bowron D.T., Teat S.J.,

    Physical Chemistry Chemical Physics, 12, No. 8, pp. 1842-1853 (2010)

    doi: 10.1039/b921160h
    Abstract



    Liquid charge-transfer (CT) complexes were observed to form on contacting electron-rich aromatics with electron withdrawing group appended 1-alkyl-4-cyanopyridinium ionic liquids (ILs). Cooling below the melting point of the ionic liquid resulted in crystallisation of ionic liquid from the complex for 2-cyano and 3-cyano pyridinium isomers and in the formation of a 1 : 1 IL : aromatic crystalline CT-complex with the 4-cyanopyridinium isomer. The liquid structure of a 1 : 1 mixture of 1-methyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl} imide with 1-methylnaphthalene has been probed by neutron diffraction experiments and molecular dynamics simulations. A high degree of correlation between the experimental data and the simulations was found with a significant displacement of the anions from around the cation by the aromatic species and the resulting structure having pi-pi stacks between the cations and the aromatic.

  5. Title: Ionic liquids through the looking glass: theory mirrors experiment and provides further insight into aromatic substitution processes

    Author(s): Jones S.G., Yau H.M., Davies E., Hook J.M., Youngs T.G.A., Harper J.B., Croft A.K.,

    Physical Chemistry Chemical Physics, 12, No. 8, pp. 1873-1878 (2010)

    doi: 10.1039/b919831h
    Abstract



    Aromatic substitution of 1-fluoro-2,4-dinitrobenzene has been shown to proceed more rapidly in an ionic liquid than in ethanol, primarily due to entropic, rather than enthalpic, effects. By using molecular dynamics simulations, an anion-pi interaction appears to contribute to strong ordering within the starting material complex that accounts for the relative differences in the SNAr k.

  6. Title: Structure and Dynamics of 1-Ethyl-3-methylimidazolium Acetate via Molecular Dynamics and Neutron Diffraction

    Author(s): Bowron D.T., D'Agostino C., Gladden L.F., Hardacre C., Holbrey J.D., Lagunas M.C., McGregor J., Mantle M.D., Mullan C.L., Youngs T.G.A.,

    Journal of Physical Chemistry B, 114, No. 23, pp. 7760-7768 (Jun 17 2010)

    Abstract


    The liquid state structure of the ionic liquid, 1-ethyl-3-methylimidazolium acetate ([C(2)mim][OAc]), an excellent nonderivitizing solvent for cellulosic biomass, has been investigated at 323 K by molecular dynamics (MD) simulation and by neutron diffraction using the SANDALS diffractometer at ISIS to provide experimental differential neutron scattering cross sections from HID isotopically substituted materials. Ion-ion radial distribution functions both calculated from MD and derived from the empirical potential structure refinement (EPSR) model to the experimental data show the alternating shell structure of anions around the cation, as anticipated. Spatial probability distributions reveal the main anion-to-cation features as in-plane interactions of anions with the three imidazolium ring hydrogens and cation-cation planar stacking above/below the imidazolium rings. Interestingly, the presence of the polarized hydrogen-bond acceptor (HBA) anion (acetate) leads to an increase in anion-anion tail-tail structuring within each anion shell, an indicator of the onset of hydrophobic regions within the anion regions of the liquid. MD simulations show the importance of scaling of the effective ionic charges in the basic simulation approach to accurately reproduce both the observed experimental neutron scattering cross sections and ion self-diffusion coefficients.

  7. Title: Small angle neutron scattering from 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids ([C(n)mim][PF6], n=4, 6, and 8)

    Author(s): Hardacre C., Holbrey J.D., Mullan C.L., Youngs T.G.A., Bowron D.T.,

    Journal of Chemical Physics B, 133, No. 7, pp. 074510- (Aug 21 2010)

    Abstract


    The presence of local anisotropy in the bulk, isotropic, and ionic liquid phases-leading to local mesoscopic inhomogeneity-with nanoscale segregation and expanding nonpolar domains on increasing the length of the cation alkyl-substituents has been proposed on the basis of molecular dynamics (MD) simulations. However, there has been little conclusive experimental evidence for the existence of intermediate mesoscopic structure between the first/second shell correlations shown by neutron scattering on short chain length based materials and the mesophase structure of the long chain length ionic liquid crystals. Herein, small angle neutron scattering measurements have been performed on selectively H/D-isotopically substituted 1-alkyl-3-methylimidazolium hexafluorophosphate ionic liquids with butyl, hexyl, and octyl substituents. The data show the unambiguous existence of a diffraction peak in the low-Q region for all three liquids which moves to longer distances (lower Q), sharpens, and increases in intensity with increasing length of the alkyl substituent. It is notable, however, that this peak occurs at lower values of Q (longer length scale) than predicted in any of the previously published MD simulations of ionic liquids, and that the magnitude of the scattering from this peak is comparable with that from the remainder of the amorphous ionic liquid. This strongly suggests that the peak arises from the second coordination shells of the ions along the vector of alkyl-chain substituents as a consequence of increasing the anisotropy of the cation, and that there is little or no long-range correlated nanostructure in these ionic liquids.

  8. Title: Simulations of imidazolium ionic liquids: when does the cation charge distribution matter?

    Author(s): Lynden-Bell R.M., Youngs T.G.A.,

    Journal of Physics: Condensed Matter, 21, No. 42, Art. No. 424120 (OCT 21 2009)

    doi: 10.1088/0953-8984/21/42/424120
    Abstract



    We compare the properties of models of liquids and crystals constructed from a number of intermolecular potentials for dimethylimidazolium chloride [dmim][Cl]. The force fields differ in the charge distribution in the cation but all include short range interactions which determine the shape of the cation. In addition to 'realistic' models intended for simulation of [dmim][Cl] we take two extreme 'unrealistic' models in which the cation charge is localized on the ring atoms or at the ring centre in order to study the effects of the cation charge distribution. The effects of polarizability are investigated by using shell models for the chloride ion. We find that, while equilibrium properties such as energetics, crystal structure, liquid structure and charge screening depend on the charge distribution in the cation but are little affected by including polarizability, dynamical properties such as diffusion are strongly affected by polarizability.

  9. Title: Evaluation of Gas Solubility Prediction in Ionic Liquids using COSMOthermX

    Author(s): Ab Manan N., Hardacre C., Jacquemin J., Rooney D.W., Youngs T.G.A.,

    Journal of Chemical and Engineering Data, 54, No. 7, pp. 2005-2022 (2009)

    doi: 10.1021/je800857x
    Abstract



    As the range of available ionic liquids increases, methods by which important engineering parameters such as gas solubilities can be estimated from simple structural information become ever more desirable. COSMO-based thermodynamic models, such as that used by COSMOthermX, allow the determination of such data for pure and mixed component systems. Herein, we evaluate the predictive capability of COSMOthermX through a comparison with literature data obtained from the IUPAC database which contains data for 15 gases in 27 ionic liquids, To determine any effect inherent to ionic liquids, gas solubility predictions were first performed for selected molecular solvents at constant temperature and pressure. Further estimations of gas solubility at temperatures ranging from (278 to 368) K at 0.1 MPa in water were performed for 14 gases. The Study has demonstrated that COSMOthermX is capable of predicting, qualitatively, gas solubilities in ionic liquids and, hence, reducing the amount of unnecessary experimental measurements prior to specific applications using ionic liquids.

  10. Title: Liquid Structure and Dynamics of Aqueous Isopropanol over gamma-Alumina

    Author(s): Youngs T.G.A., Weber D., Gladden L.F., Hardacre C.,

    Journal of Physical Chemistry C, 113, No. 51, pp. 21342-21352 (2009)

    doi: 10.1021/jp906677c
    Abstract



    The liquid structures of thin films of aqueous solutions of 0, 7, 19, 50, and 100 mol % isopropanol above O/Al-terminated gamma-alumina < 001 > surfaces have been investigated by means of classical molecular dynamics simulations. The structuring effect of the oxide oil the liquid mixtures is strong and heavily dependent on the local structure of the oxide. Two distinct re-ions are found oil the oxide Surface characterized by the degree of coordination of Al atoms. Above octahedral Al atoms, water and isopropanol molecules adsorb via the oxygen atoms to maximize the electrostatic interaction, whereas above tetrahedral Al sites the solvent molecules adsorb via hydrogen atoms with the oxygen atoms away front the surface. More mobility is found in the second layer compared with the first; however, its structure is still influenced significantly by the orientation of molecules in the first adsorbed layer. Qualitatively, the displacement of water from the surface by the adsorption of isopropanol occurs with 2.6 Water molecules lost for every alcohol molecule present based on the effective surface areas of the two species calculated from the pure simulations. Diffusion in the liquid has been investigated by both molecular dynamics and PFG-NMR Studies. Both show that the first adsorbed layer is slower moving than the bulk by several orders of magnitude, as expected, and thereafter the simulations show a gradual increase in diffusivity with increasing distance from the interface, lending toward the bulk value. Experimental diffusion coefficients of isopropanol inside the gamma-alumina pore are found to be approximately one-quarter of that found in the bulk liquid. When compared with the simulated Values, this suggests that the Surface properties probed by the NMR technique encompass the first two layers interacting with the surface. In addition, because of the time scale of the measurements, the largest diffusion coefficient obtained includes the pore tortuosity and, therefore, a reduced experimental value is found compared with that obtained front the simulations.

  11. Title: The importance of solvent reorganisation in the effect of an ionic liquid on a unimolecular substitution process

    Author(s): Yau H.M., Barnes S.A., Hook J.M., Youngs T.G.A., Croft A.K., Harper J.B.,

    Chemical Communications, No. 30, pp. 3576-3578 (2008)

    doi: 10.1039/b805255g
    Abstract



    Temperature dependent rate studies demonstrate an enthalpic bene. t and an entropic cost associated with the change in the rate of a unimolecular substitution process on addition of a high proportion of an ionic liquid, the latter e. ect being supported by molecular dynamics simulations.

  12. Title: Simulations of ionic liquids, solutions, and surfaces

    Author(s): Lynden-Bell R.M., Del Popolo M.G., Youngs T.G.A., Kohanoff J., Hanke C.G., Harper J.B., Pinilla C.C.

    Accounts of Chemical Research, 40, No. 11, pp. 1138-1145 (OCT 2007)

    doi: 10.1021/ar700065s
    Abstract



    We have been using atomistic simulation for the last 10 years to study properties of imidazolium-based ionic liquids. Studies of dissolved molecules show the importance of electrostatic interactions in both aromatic and hydrogen-bonding solutes. However, the local structure strongly depends upon ion–ion and solute–solvent interactions. We find interesting local alignments of cations at the gas–liquid and solid–liquid interfaces, which give a potential drop through the surface. If the solid interface is charged, this charge is strongly screened over distances of a few nanometres and this screening decays on a fast time scale. We have studied the sensitivity of the liquid structure to force-field parameters and show that results from ab initio simulations can be used in the development of force fields.

  13. Title: Glucose solvation by the ionic liquid 1,3-dimethylimidazolium chloride: A simulation study

    Author(s): Youngs T.G.A., Hardacre C., Holbrey J.D.,

    J. Phys. Chem. B, 111, pp. 13765-13774 (2007)

    doi: 10.1021/Jp076728k
    Abstract



  14. Title: Structure and solvation in ionic liquids

    Author(s): Hardacre C., Holbrey J.D., Nieuwenhuyzen M., Youngs T.G.A.,

    Acc. Chem. Res., 40, pp. 1146-1155 (2007)

    doi: 10.1021/ar700068x
    Abstract



  15. Title: Using DL_POLY to study the sensitivity of liquid structure to potential parameters

    Author(s): Lynden-Bell R.M., Youngs T.G.A.

    Molecular Simulation, 32, No. 12-13, pp. 1025-1033 (OCT-NOV 2006)

    doi: 10.1080/08927020600823133
    Abstract



    Two case studies are presented showing the local structure in liquids and how it responds to changes in the intermolecular potential. The idea is to use realistic and unrealistic potentials in order to determine the sensitivity of local liquid structure to potential parameters. The first case study concerns two families of modified water models. In the "hybrid" family, the hydrogen bond strength is reduced, but the geometry kept constant; in the second family, the molecular geometry is changed by reducing the bond angle, keeping a constant molecular dipole moment. The local structure is measured by radial distribution functions, three-dimensional probability distribution functions and three-body angular correlations. The second case study concerns the ionic liquid dimethylimidazolium chloride ([C(1)mim]Cl). The effect of reducing the hydrogen bonding potential of the cations while maintaining their charge is examined.

  16. Title: A molecular dynamics study of glucose solvation in the ionic liquid 1,3-dimethylimidazolium chloride

    Author(s): Youngs T.G.A., Holbrey J.D., Deetlefs M., Nieuwenhuyzen M., Gomes M.F.C., Hardacre C.

    Chemphyschem, 7, No. 11, pp. 2279-2281 (NOV 13 2006)

    doi: 10.1002/cphc.200600569
    Abstract



  17. Title: Molecular electrostatic properties of ions in an ionic liquid

    Author(s): Prado C.E.R., Del Popolo M.G., Youngs T.G.A., Kohanoff J., Lynden-Bell R.M.

    Molecular Physics, 104, No. 15, pp. 2477-2483 (AUG 10 2006)

    doi: 10.1080/00268970600765748
    Abstract



    We have analysed the electronic wave functions from an ab initio simulation of the ionic liquid ( room temperature molten salt) dimethyl imidazolium chloride ([dmim][Cl] or [C(1)mim][CI]) using localized Wannier orbitals. This allows us to assign electron density to individual ions. The probability distributions of the ionic dipole moments for an isolated ion and for ions in solution are compared. The liquid environment is found to polarize the cation by about 0.7D and to increase the amplitude of the fluctuations in the dipole moments of both cation and anion. The relative changes in nuclear and electronic contributions are shown. The implications for classical force fields are discussed.

  18. Title: New bis(triazinyl) pyridines for selective extraction of americium(III)

    Author(s): Hudson M.J., Boucher C.E., Braekers D., Desreux J.F., Drew M.G.B., Foreman M.R.S., Harwood L.M., Hill C., Madic C., Marken F., Youngs T.G.A.

    New Journal Of Chemistry, 30, No. 8, pp. 1171-1183 (AUG 2006)

    doi: 10.1039/b514108g
    Abstract



    New hydrophobic, tridentate nitrogen heterocyclic reagents (BATPs) such as 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl) pyridine (1) and 2,6-bis(9,9,10,10-tetramethyl-9,10-dihydro-1,2,4-triaza-anthrane-3-yl) pyridine (2) have been studied. I is resistant to hydrolysis in 3 M nitric acid, whereas 2 is resistant to both acid hydrolysis and radiolysis. The molecules are able to give significantly enhanced separations of americium(III) from an excess of europium(III) in nitric acid. Typically, for 1 D-Am = 500 and SFAm,/Eu = 5000 compared with D-Am = 30 and SFAm /Eu = 400 with the reference molecule 2,6-bis(isopropyl[1,2,4]triazin-3-yl) pyridine (7). In order to increase the stability of 1 and 2, the labile alpha-benzylic hydrogens that are present in 7 have been replaced by alkyl groups. Three molecules of 1 are able to enclose completely the coordination sphere of the M(III) in the crystal structure of [Y(1)(3)][Y(NO3)(5)]center dot NO3 center dot 2.5H(2)O.

  19. Title: Dissociative electron attachment to HCCCN

    Author(s): Graupner K., Merrigan T.L., Field T.A., Youngs T.G.A., Marr P.C.

    New Journal Of Physics, 8, Art. No. 117 (JUL 20 2006)

    doi: 10.1088/1367-2630/8/7/117
    Abstract



    Dissociative electron attachment to cyanoacetylene (propiolonitrile) HCCCN has been observed in the electron energy range 0-12 eV. Negative ions are formed in two main bands with maxima at similar to 1.6 eV (CCCN-) and similar to 5.3 eV (CCCN-, CN-, HCC- and CC-). There are also weaker resonances which lead to dissociative electron attachment to form CN-, HCC- and CC- with a maximum intensity at similar to 8.1 eV and CCCN-, CN- and CC- at similar to 11.2 eV. A trace of CCN- is observed at similar to 9.1 eV. The positions of the main dissociative attachment bands observed are close to positions of pi* resonances recently calculated by Sommerfeld and Knecht. Calculations have also been performed in this work, which confirm the position of the p* orbitals. The electron affinity of the CCCN radical is determined as 4.59 +/- 0.25 eV from the threshold for CCCN- formation at 1.32 +/- 0.15 eV. Dissociative electron attachment to this molecule will act as a source of negative ions in extraterrestrial environments where electrons are present with more than 1.3 eV energy.

  20. Title: Development of complex classical force fields through force matching to ab initio data: Application to a room-temperature ionic liquid

    Author(s): Youngs T.G.A., Del Popolo M.G., Kohanoff J.

    Journal Of Physical Chemistry B, 110, No. 11, pp. 5697-5707 (MAR 23 2006)

    doi: 10.1021/jp056931k
    Abstract



    Recent experimental neutron diffraction data and ab initio molecular dynamics simulation of the ionic liquid dimethylimidazolium chloride ([dmim]Cl) have provided a structural description of the system at the molecular level. However, partial radial distribution functions calculated front the latter, when compared to previous classical Simulation results, highlight some limitations in the structural description offered by force field-based simulations. With the availability of ab initio data it is possible to improve the classical description of [dmim]Cl by using the force matching approach, and the strategy for fitting complex force fields in their original functional form is discussed. A self-consistent optimization rnethod for the generation of classical potentials of general functional forill is presented and applied, and a force field that better reproduces the observed first principles forces is obtained. When used in Simulation, it predicts structural data which reproduces more faithfully that observed in the ab initio studies. Some possible refinements to the technique, its application, and the general Suitability of common potential energy functions used within many ionic liquid force fields are discussed.

  21. Title: Fragrance release from the surface of branched poly(amide)s

    Author(s): Aulenta F., Drew M.G.B., Foster A., Hayes W., Rannard S., Thornthwaite D.W., Youngs T.G.A.

    Molecules, 10, No. 1, pp. 81-97 (JAN 2005)

    Abstract

    Full Text

    Enzymes are powerful tools in organic synthesis that are able to catalyse a wide variety of selective chemical transformations under mild and environmentally friendly conditions. Enzymes such as the lipases have also found applications in the synthesis and degradation of polymeric materials. However, the use of these natural catalysts in the synthesis and the post-synthetic modification of dendrimers and hyperbranched molecules is an application of chemistry yet to be explored extensively. In this study the use of two hydrolytic enzymes, a lipase from Candida cylindracea and a cutinase from Fusarium solani pisii, were investigated in the selective cleavage of ester groups situated on the peripheral layer of two families of branched polyamides. These branched polyamides were conjugated to simple fragrances citronellol and L-menthol via ester linkages. Hydrolysis of the ester linkage between the fragrances and the branched polyamide support was carried out in aqueous buffered systems at slightly basic pH values under the optimum operative conditions for the enzymes used. These preliminary qualitative investigations revealed that partial cleavage of the ester functionalities from the branched polyamide support had occurred. However, the ability of the enzymes to interact with the substrates decreased considerably as the branching density, the rigidity of the structure and the bulkiness of the polyamide-fragrance conjugates increased.

  22. Title: Synthesis and characterization of fluorescent poly(aromatic amide) dendrimers

    Author(s): Aulenta F., Drew M.G.B., Foster A., Hayes W., Rannard S., Thornthwaite D.W., Worrall D.R., Youngs T.G.A.

    Journal Of Organic Chemistry, 70, No. 1, pp. 63-78 (JAN 7 2005)

    doi: 10.1021/jo048799a
    Abstract



    The synthesis of a series of poly(aromatic amide) dendrimers up to the second generation is described herein. The AB, building block used throughout the synthesis of the dendrimers was the allyl ester of 3,5-diaminocinnamic acid, which has been synthesized from 3,5-dinitrobenzoic acid in good yield with use of a four-step procedure. Dendron synthesis was achieved via a convergent approach with use of a sequence of deprotection/coupling steps. Two commercially available alcohols, L-menthol and citronellol, were coupled to the AB(2) monomer by using an alkyl diacid spacer and two core units; 1,7-diaminoheptane and tris(2-aminoethyl)amine have been used to produce the final dendrimers. Characterization was carried out by NMR and IR spectroscopies, MALDI-TOF mass spectrometry, GPC, and DSC. The novel monomer and dendritic derivatives exhibited a strong fluorescence emission in the visible region (lambda approximate to 500 nm) of the spectrum and a weak emission in the near-infrared (lambda approximate to 850 nm) upon excitation in the near-UV region. The fluorescence emission characteristics were found to be solvent and dendrimer generation dependent.

  23. Title: QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes

    Author(s): Drew M.G.B., Hudson M.J., Youngs T.G.A.

    Journal Of Alloys And Compounds, 374, No. 1-2, pp. 408-415 (JUL 14 2004)

    doi: 10.1016/j.jallcom.2003.11.047
    Abstract



    Quantitative structure activity relationships (QSARs) have been developed to optimise the choice of nitrogen heterocyclic molecules that can be used to separate the minor actinides such as americium(III) from europium(III) in the aqueous PUREX raffinate of nuclear waste. Experimental data on distribution coefficients and separation factors (SFs) for 47 such ligands have been obtained and show SF values ranging from 0.61 to 100. The ligands were divided into a training set of 36 molecules to develop the QSAR and a test set of 11 molecules to validate the QSAR. Over 1500 molecular descriptors were calculated for each heterocycle and the Genetic Algorithm was used to select the most appropriate for use in multiple regression equations. Equations were developed fitting the separation factors to 6-8 molecular descriptors which gave r(2) values of >0.8 for the training set and values of >0.7 for the test set, thus showing good predictive quality. The descriptors used in the equations were primarily electronic and steric. These equations can be used to predict the separation factors of nitrogen heterocycles not yet synthesised and/or tested and hence obtain the most efficient ligands for lanthanide and actinide separation. (C) 2003 Elsevier B.V. All rights reserved.

  24. Title: Separation of lanthanides and actinides(III) using tridentate benzimidazole, benzoxazole and benzothiazole ligands

    Author(s): Drew M.G.B., Hill C., Hudson M.J., Iveson P.B., Madic C., Vaillant L., Youngs T.G.A.

    New Journal Of Chemistry, 28, No. 4, pp. 462-470 (APR 2004)

    doi: 10.1039/b314321j
    Abstract



    The ability of new hydrophobic tridentate ligands based on 2,6-bis(benziinidazol-2-yl)pyridine, 2,6-bis(benzoxazol-2-yl)pyridine and 2,6-bis(benzothiazol-2-yl)pyridine to selectively extract americium(III) from europium(III) was measured. The most promising ligand-2,6-bis(benzoxazol-2-yl)-4-(2-decyl-1-tetradecyloxy)pyridine L-9 was found to give separation factors (SFAm/Eu) of up to 70 when used to extract cations from 0.02-0.10 M HNO3 into TPH in synergy with 2-bromodecanoic acid. Six structures of lanthanide complexes with 2,6-bis(benzoxazol-2-yl)pyridine L-6 were then determined to evaluate the types of species that are likely to be involved in the separation process. Three structural types were observed, namely [LnL(6)(NO3)(3)(H2O)2], 11-coordinate only for La, [LnL(6) (NO3)(3) (CH3CN)], 10-coordinate for Pr, Nd and Eu and [LnL(6) (NO3)(3)(H2O)], L 10-coordinate for Eu and Gd. Quantum Mechanics calculations were carried out on the tridentate ligands to elucidate the conformational preferences of the ligands in the free state and protonated and diprotonated forms and to assess the electronic properties of the ligands for comparison with other terdentate ligands used in lanthanide/actinide separation processes.

  25. Title: Solvent extraction and lanthanide complexation studies with new terdentate ligands containing two 1,3,5-triazine moieties

    Author(s): Drew M.G.B., Hill C., Hudson M.J., Iveson P.B., Madic C., Youngs T.G.A.

    Dalton Transactions, No. 2, pp. 244-251 (2004)

    doi: 10.1039/b312582c
    Abstract



    The extracting agent 2,6-bis(4,6-di-pivaloylamino-1,3,5-triazin-2-yl)-pyridine (L-5) in n-octanol was found, in synergy with 2-bromodecanoic acid, to give D-Am/D-Eu separation factors (SFs) between 2.4 and 3.7 when used to extract the metal ions from 0.02-0.12 M HNO3. Slightly higher SFs (4-6) were obtained in the absence of the synergist when the ligand was used to extract Am(III) and Eu(III) from 0.98 M HNO3. In order to investigate the possible nature of the extracted species crystal structures of L-5 and the complex formed between Yb(III) with 2,6-bis(4,6-di-amino-1,3,5-triazin-2-yl)-pyridine (L-4) were also determined. The structure of L-5 shows 3 methanol solvent molecules all of which form 2 or 3 hydrogen bonds with triazine nitrogen atoms, amide nitrogen or oxygen atoms, or pyridine nitrogen atoms. However, L-5 is relatively unstable in metal complexation reactions and loses amide groups to form the parent tetramine L-4. The crystal structure of Yb(L-4)(NO3)(3) shows ytterbium in a 9-coordinate environment being bonded to three donor atoms of the ligand and three bidentate nitrate ions. The solvent extraction properties of L-4 and L-5 are far inferior to those found for the 2,6-bis-(1,2,4-triazin-3-yl)-pyridines (L-1) which have SF values of ca. 140 and theoretical calculations have been made to compare the electronic properties of the ligands. The electronic charge distribution in L-4 and L-5 is similar to that found in other terdentate ligands such as terpyridine which have equally poor extraction properties and suggests that the unique properties of L-1 evolve from the presence of two adjacent nitrogen atoms in the triazine rings.

  26. Title: The coordination chemistry of 1,2,4-triazinyl bipyridines with lanthanide(III) elements - implications for the partitioning of americium(III)

    Author(s): Hudson M.J., Drew M.G.B., Foreman M.R.S., Hill C., Huet N., Madic C., Youngs T.G.A.

    Dalton Transactions, No. 9, pp. 1675-1685 (2003)

    doi: 10.1039/b301178j
    Abstract



    It has been established that 6-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2'-bipyridines (R,hemi-BTPs) have properties which are intermediate between those of the terpyridines and the bis(1,2,4-triazin-3-yl)pyridines (BTPs). However, they resemble the terpyridines much more closely than the BTPs. It has been shown that Et, hemi-BTP when dissolved in TPH-a dodecane-like solvent-is a selective reagent for the separation of americium(III) from europium(III). Solution NMR in acetonitrile largely confirmed the crystallographic results. There was no evidence for a 1 : 3 complex cation, or for significant differences between metal(III)-N distances for the pyridine and 1,2,4-triazine rings. Intramolecular hydrogen bonding plays a crucial role in the formation of metal coordination spheres, which explains the differences between the terpyridyl, R,hemi-BTPs and the BTPs. Protonation of the R,hemi-BTPs facilitates a conformational change which is necessary for complexation.

  27. Title: Americium(III) and europium(III) solvent extraction studies of amide-substituted triazine ligands and complexes formed with ytterbium(III)

    Author(s): Boubals N., Drew M.G.B., Hill C., Hudson M.J., Iveson P.B., Madic C., Russell M.L., Youngs T.G.A.

    Journal Of The Chemical Society-Dalton Transactions, No. 1, pp. 55-62 (JAN 7 2002)

    doi: 10.1039/b104181a
    Abstract



    4-Amino-bis(2,6-(2-pyridyl))-1,3,5-triazine L-4 and several, amide derivatives with hydrophobic alkyl substituents have been synthesised. Solvent extraction studies carried out on Am(III) and Eu(III) with L-4 and its amide derivatives in synergistic combination with alpha-bromodecanoic acid, show that these ligands can selectively extract actinides with respect to lanthanides. The structures of [H2L4].2Cl.2.5H(2)O and two amide derivatives have been determined and show respectively the trans, trans; cis, cis; and cis, trans conformations of the adjacent aromatic rings. These observed conformations are in agreement with the results of quantum mechanics calculations on L-4 and its protonated derivatives. The structures of two Yb complexes with amide derivatives are also reported with stoichiometry [Yb(L)(NO3)(H2O)(4)].2NO(3).0.5H(2)O and [Yb(L)(NO3)(3)(H2O)].2MeCN and show the metal in 9 coordinate environments.