75 results found
Turnell-Ritson RC, Sapsford JS, Cooper RT, et al., 2018, Base-induced reversible H-2 addition to a single Sn(II) centre, Chemical Science, Vol: 9, Pages: 8716-8722, ISSN: 2041-6520
A range of amines catalyse the oxidative addition (OA) of H2 to [(Me3Si)2CH]2Sn (1), forming [(Me3Si)2CH]2SnH2 (2). Experimental and computational studies point to ‘frustrated Lewis pair’ mechanisms in which 1 acts as a Lewis acid and involve unusual late transition states; this is supported by the observation of a kinetic isotope effect Image ID:c8sc03110j-t1.gif for Et3N. When DBU is used the energetics of H2 activation are altered, allowing an equilibrium between 1, 2 and adduct [1·DBU] to be established, thus demonstrating reversible oxidative addition/reductive elimination (RE) of H2 at a single main group centre.
Heller BSJ, Kolbeck C, Niedermaier I, et al., 2018, Surface enrichment in equimolar mixtures of non-functionalized and functionalized imidazolium-based ionic liquids, ChemPhysChem, Vol: 19, Pages: 1733-1745, ISSN: 1439-7641
For equimolar mixtures of ionic liquids with imidazolium‐based cations of very different electronic structure, we observe very pronounced surface enrichment effects by angle‐resolved X‐ray photoelectron spectroscopy (XPS). For a mixture with the same anion, that is, 1‐methyl‐3‐octylimidazolium hexafluorophosphate+1,3‐di(methoxy)imidazolium hexafluorophosphate ([C8C1Im][PF6]+[(MeO)2Im][PF6]), we find a strong enrichment of the octyl chain‐containing [C8C1Im]+ cation and a corresponding depletion of the [(MeO)2Im]+ cation in the topmost layer. For a mixture with different cations and anions, that is, [C8C1Im][Tf2N]+[(MeO)2Im][PF6], we find both surface enrichment of the [C8C1Im]+ cation and the [Tf2N]− (bis[(trifluoromethyl)sulfonyl]imide) anion, while [(MeO)2Im]+ and [PF6]− are depleted from the surface. We propose that the observed behavior in these mixtures is due to a lowering of the surface tension by the enriched components. Interestingly, we observe pronounced differences in the chemical shifts of the imidazolium ring signals of the [(MeO)2Im]+ cations as compared to the non‐functionalized cations. Calculations of the electronic structure and the intramolecular partial charge distribution of the cations contribute to interpreting these shifts for the two different cations.
Fogarty RM, Matthews RP, Ashworth CR, et al., 2018, Experimental validation of calculated atomic charges in ionic liquids, Journal of Chemical Physics, Vol: 148, ISSN: 0021-9606
A combination of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy has been used to provide an experimental measure of nitrogen atomic charges in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital population analysis, and the atoms in molecules approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of the charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (<0.3 e) should be interpreted with care. We use these validated charges to provide physical insight into nitrogen atomic charges for the ILs probed.
Heid E, Hunt PA, Schroeder C, 2018, Evaluating excited state atomic polarizabilities of chromophores, Physical Chemistry Chemical Physics, Vol: 20, Pages: 8554-8563, ISSN: 1463-9076
Ground and excited state dipoles and polarizabilities of the chromophores N-methyl-6-oxyquinolinium betaine (MQ) and coumarin 153 (C153) in solution have been evaluated using time-dependent density functional theory (TD-DFT). A method for determining the atomic polarizabilities has been developed; the molecular dipole has been decomposed into atomic charge transfer and polarizability terms, and variation in the presence of an electric field has been used to evaluate atomic polarizabilities. On excitation, MQ undergoes very site-specific changes in polarizability while C153 shows significantly less variation. We also conclude that MQ cannot be adequately described by standard atomic polarizabilities based on atomic number and hybridization state. Changes in the molecular polarizability of MQ (on excitation) are not representative of the local site-specific changes in atomic polarizability, thus the overall molecular polarizability ratio Image ID:c7cp08549d-t1.gif does not provide a good approximation for local atom-specific polarizability changes on excitation. Accurate excited state force fields are needed for computer simulation of solvation dynamics. The chromophores considered in this study are often used as molecular probes. The methods and data reported here can be used for the construction of polarizable ground and excited state force fields. Atomic and molecular polarizabilities (ground and excited states) have been evaluated over a range of functionals and basis sets. Different mechanisms for including solvation effects have been examined; using a polarizable continuum model, explicit solvation and via sampling of clusters extracted from a MD simulation. A range of different solvents have also been considered.
Addicoat M, Atkin R, Lopes JNC, et al., 2018, Structure and dynamics of ionic liquids: general discussion, FARADAY DISCUSSIONS, Vol: 206, Pages: 291-337, ISSN: 1359-6640
Fogarty RM, Rowe R, Matthews RP, et al., 2018, Atomic charges of sulfur in ionic liquids: experiments and calculations, FARADAY DISCUSSIONS, Vol: 206, Pages: 183-201, ISSN: 1359-6640
Fogarty RM, Matthews RP, Clough MT, et al., 2017, NEXAFS spectroscopy of ionic liquids: experiments versus calculations, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 19, Pages: 31156-31167, ISSN: 1463-9076
Kuzmina O, Hassan NH, Patel L, et al., 2017, The impact of ionic liquids on the coordination of anions with solvatochromic copper complexes, DALTON TRANSACTIONS, Vol: 46, Pages: 12185-12200, ISSN: 1477-9226
Brooks NJ, Castiglione F, Doherty CM, et al., 2017, Linking the structures, free volumes, and properties of ionic liquid mixtures, CHEMICAL SCIENCE, Vol: 8, Pages: 6359-6374, ISSN: 2041-6520
Hunt PA, 2017, Quantum Chemical Modeling of Hydrogen Bonding in Ionic Liquids, TOPICS IN CURRENT CHEMISTRY, Vol: 375, ISSN: 2365-0869
Ward BJ, Hunt PA, 2017, Hydrophosphination of Styrene and Polymerization of Vinylpyridine: A Computational Investigation of Calcium-Catalyzed Reactions and the Role of Fluxional Noncovalent Interactions, ACS CATALYSIS, Vol: 7, Pages: 459-468, ISSN: 2155-5435
Ashworth CR, Matthews RP, Welton T, et al., 2016, Doubly ionic hydrogen bond interactions within the choline chloride-urea deep eutectic solvent, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 18, Pages: 18145-18160, ISSN: 1463-9076
Kuzmin O, Bordes E, Schmauck J, et al., 2016, Solubility of alkali metal halides in the ionic liquid [C(4)C(1)im][OTf], PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 18, Pages: 16161-16168, ISSN: 1463-9076
Clough MT, Geyer K, Hunt PA, et al., 2016, Azoniaspiro salts: towards bridging the gap between room-temperature ionic liquids and molten salts, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 18, Pages: 3339-3351, ISSN: 1463-9076
Lau GV, Hunt PA, Mueller EA, et al., 2015, Water droplet excess free energy determined by cluster mitosis using guided molecular dynamics, JOURNAL OF CHEMICAL PHYSICS, Vol: 143, ISSN: 0021-9606
Clough M, Grasvik J, Hunt P, et al., 2015, Physicochemical investigation of ionic liquid mixtures, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Clough M, Geyer K, Hunt P, et al., 2015, Ionic liquids: Not always innocent solvents for cellulose, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Lau GV, Ford IJ, Hunt PA, et al., 2015, Surface thermodynamics of planar, cylindrical, and spherical vapour-liquid interfaces of water, JOURNAL OF CHEMICAL PHYSICS, Vol: 142, ISSN: 0021-9606
Hunt PA, Ashworth CR, Matthews RP, 2015, Hydrogen bonding in ionic liquids, CHEMICAL SOCIETY REVIEWS, Vol: 44, Pages: 1257-1288, ISSN: 0306-0012
Clough MT, Geyer K, Hunt PA, et al., 2015, Ionic liquids: not always innocent solvents for cellulose, GREEN CHEMISTRY, Vol: 17, Pages: 231-243, ISSN: 1463-9262
Scarbath-Evers LK, Hunt PA, Kirchner B, et al., 2015, Molecular features contributing to the lower viscosity of phosphonium ionic liquids compared to their ammonium analogues, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 20205-20216, ISSN: 1463-9076
Xue L, Tamas G, Matthews RP, et al., 2015, An OHD-RIKES and simulation study comparing a benzylmethylimidazolium ionic liquid with an equimolar mixture of dimethylimidazolium and benzene, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 9973-9983, ISSN: 1463-9076
Matthews RP, Welton T, Hunt PA, 2015, Hydrogen bonding and pi-pi interactions in imidazolium-chloride ionic liquid clusters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 14437-14453, ISSN: 1463-9076
Clough MT, Crick CR, Grasvik J, et al., 2015, A physicochemical investigation of ionic liquid mixtures, CHEMICAL SCIENCE, Vol: 6, Pages: 1101-1114, ISSN: 2041-6520
Matthews RP, Ashworth C, Welton T, et al., 2014, The impact of anion electronic structure: similarities and differences in imidazolium based ionic liquids, JOURNAL OF PHYSICS-CONDENSED MATTER, Vol: 26, ISSN: 0953-8984
Mac Dowell N, Llovell F, Sun N, et al., 2014, New Experimental Density Data and Soft-SAFT Models of Alkylimidazolium ([C(n)C(1)im](+)) Chloride (Cl-), Methylsulfate ([MeSO4](-)), and Dimethylphosphate ([Me2PO4](-)) Based Ionic Liquids, JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 118, Pages: 6206-6221, ISSN: 1520-6106
Matthews RP, Welton T, Hunt PA, 2014, Competitive pi interactions and hydrogen bonding within imidazolium ionic liquids, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 3238-3253, ISSN: 1463-9076
Herrington TJ, Ward BJ, Doyle LR, et al., 2014, Bypassing a highly unstable frustrated Lewis pair: dihydrogen cleavage by a thermally robust silylium-phosphine adduct, CHEMICAL COMMUNICATIONS, Vol: 50, Pages: 12753-12756, ISSN: 1359-7345
Skarmoutsos I, Welton T, Hunt PA, 2014, The importance of timescale for hydrogen bonding in imidazolium chloride ionic liquids, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 3675-3685, ISSN: 1463-9076
Ge L, Bernasconi L, Hunt P, 2013, Linking electronic and molecular structure: insight into aqueous chloride solvation., Phys Chem Chem Phys, Vol: 15, Pages: 13169-13183
Aqueous chloride solutions are ubiquitous and diverse; systems include sea water, atmospheric droplets, geological processes and biological organisms. However, despite considerable effort, a complete microscopic model of the hydration shell, and local electronic structure of the aqueous chloride ion and its dynamics has not been established. In this work we employ ab initio molecular dynamics to study an aqueous chloride solution. In particular, local solvation events and the electronic structure around the chloride ion are interrogated. We employ the Effective Molecular Orbital (EMO) method which partitions the electronic structure into solute and solvent components while maintaining a rigorous quantum mechanical description of both. Movement of the chloride highest occupied molecular orbital (HOMO) energy within the valence band of water is revealed. The chloride ion has little impact on the average water electronic structure, however, locally the electronic effect of the chloride ion is significant. With the Hofmeister series in mind we find that the electronic effect of the chloride ion extends beyond the first solvation shell, but not beyond the edge of the second solvation shell. The chloride ion sits near the centre of the Hofmeister series because of an essential degeneracy between water-water and water-Cl H-bonding and because of a strong similarity in the water and chloride electronic structure. The chloride ion prefers to be symmetrically solvated by six H-bonding water molecules, however, the chloride HOMO energy and the coordination number oscillate in response to local fluctuations driven by the dynamics of the bulk water. A combined structural and electronic analysis has led to a distinction between two types of water molecule within the first solvation shell, those that H-bond to the chloride ion, and those that remain local (i.e. within the first solvation shell) but which H-bond to other water molecules. There are indications that these exhibit dif
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