BF4 as a probe for ion pair solution structure using interionic one‐ and two‐dimensional 19F{1H} NOEs

Hofstetter, Christine; Pochapsky, Thomas C.

doi:10.1002/(sici)1097-458x(200002)38:2<90::aid-mrc608>3.3.co;2-g

Cited by 7 publications

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“…5.3 Å, from the reported solid-state structure for the Bu 4 N cation entrapped in a cationic host [made up of a tetrahedral coordination cage containing 24+ charges with M 12 L 6 stoichiometry where M = (en)Pd 2+ and L denotes a 1,4-bis(3,5-pyrimidyl)benzene], and (b) close to the r H value, ca. 4.9 Å, calculated from the diffusion data of Pochapsky et al for the Bu 4 NCl in a 1.5 mM chloroform solution 20a 2 Complex 3 …”

Section: Resultsmentioning

confidence: 99%

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

2005

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(1)H, (19)F, and (7)Li pulsed gradient spin-echo (PGSE) NMR measurements for a series of salts are reported. The (7)Li is shown to complement the (1)H and (19)F measurements; however, the use of higher concentrations (for the less-sensitive (7)Li) can lead to aggregation. For all of the salts discussed {Li(BF(4)); (n-Bu(4)N)(BF(4)), a trinuclear Ru cluster; [Ir(1,5-COD)(4)](BF(4)), where 4 is a chiral P,N ligand; and the crown ether stabilized potassium salt, [K(18-crown-6)(NPh(2))], 6}, the use of THF seems to promote strong ion pairing. In several cases, the degree of ion pairing approaches 100%. In THF solution, the potassium salt, 6, prefers to exist as a more classical ion pair rather than as the pi complex found in the solid state. In some cases, (1)H, (1)H NOESY and (1)H, (19)F HOESY spectra help to pinpoint the cation/anion spatial relationship.

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Section: Resultsmentioning

confidence: 99%

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

2005

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“…Moreover, the difference in the electron density between the surface layers of [bmim][BF 4 ] and [bmim][PF 6 ], which have the same [bmim] + cation, should stem from the different size, and number of electrons, of the respective anions. Using the ionic radii of PF 6 - (2.76 Å) and BF 4 - (2.20 Å), we obtain the electron densities of ρ PF 6 ≈ 0.78 e/Å 3 and ρ BF 4 ≈ 0.92 e/Å 3 for the two anions, respectively…”

Section: Discussionmentioning

confidence: 99%

Surface Layering in Ionic Liquids: An X-ray Reflectivity Study

et al. 2005

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The surface structure and thermodynamics of two ionic liquids, based on the 1-alkyl-3-methylimidazolium cations, were studied by X-ray reflectivity and surface tensiometry. A molecular layer of a density approximately 18% higher than that of the bulk is found to form at the free surface of these liquids. In common with surface layering in liquid metals and surface freezing in melts of organic chain molecules, this effect is induced by the lower dimensionality of the surface. The concentrations of the oppositely charged ions within the surface layer are determined by chemical substitution of the anion. The temperature-dependent surface tension measurements reveal a normal, negative-slope temperature dependence. The different possible molecular arrangements within the enhanced-density surface layer are discussed.

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“…For this reason, there is nowadays a growing interest aimed at elucidating the structure of transition-metal complexes in solution. Very useful NMR procedures have been developed for this purpose, with special emphasis on the interaction between cationic complexes and fluorine-containing anions .…”

Section: Introductionmentioning

confidence: 99%

The Structure of ([W₃Q₄X₃(dmpe)₃]⁺, Y^-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF₄, PF₆, dmpe = Me₂PCH₂CH₂PMe₂) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W₃S₄H₃(dmpe)₃]⁺

et al. 2006

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The 1H,19F HOESY spectra of the title compounds in CD2Cl2 solution indicate that the cluster cations form ion pairs with the BF4- and PF6- anions with a well-defined interionic structure that appears to be basically determined essentially by the nature of the X- ligand. For the clusters with X = H and OH, the structure of the ion pairs is such that the counteranion (Y-) and the X- ligands are placed close to each other. However, when the size and electron density of X- increase (X = Br), Y- is forced to move to a different site, far away from X-. The relevance of ion-pairing on the chemistry of these compounds is clearly seen through a decrease in the rate of proton transfer from HCl to the hydride cluster [W3S4H3(dmpe)3]+ in the presence of an excess of BF4-. The kinetic data for this reaction can be rationalized by considering that the ([W3S4H3(dmpe)3]+, BF4-) ion pairs are unproductive in the proton-transfer process. Theoretical calculations indicate that the real behavior can be more complex. Although the cluster can still form adducts with HCl in the presence of BF4-, the structures of the most-stable BF4--containing HCl adducts show H...H distances too large to allow the subsequent release of H2. In addition, the effective concentration of HCl is also reduced because of the formation of adducts as ClH...BF4-. As a consequence of both effects, the proton transfer takes place more slowly than for the case of the dihydrogen-bonded HCl adduct resulting from the unpaired cluster.

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BF4 as a probe for ion pair solution structure using interionic one‐ and two‐dimensional 19F{1H} NOEs

Cited by 7 publications

References 0 publications

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

Surface Layering in Ionic Liquids: An X-ray Reflectivity Study

The Structure of ([W₃Q₄X₃(dmpe)₃]⁺, Y^-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF₄, PF₆, dmpe = Me₂PCH₂CH₂PMe₂) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W₃S₄H₃(dmpe)₃]⁺

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BF4 as a probe for ion pair solution structure using interionic one‐ and two‐dimensional 19F{1H} NOEs

Cited by 7 publications

References 0 publications

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

Multinuclear PGSE Diffusion and Overhauser NMR Studies on a Variety of Salts in THF Solution

Surface Layering in Ionic Liquids: An X-ray Reflectivity Study

The Structure of ([W3Q4X3(dmpe)3]+, Y-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF4, PF6, dmpe = Me2PCH2CH2PMe2) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W3S4H3(dmpe)3]+

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The Structure of ([W₃Q₄X₃(dmpe)₃]⁺, Y^-) Ion Pairs (Q = S, Se; X = H, OH, Br; Y = BF₄, PF₆, dmpe = Me₂PCH₂CH₂PMe₂) in Dichloromethane Solution and the Effect of Ion-Pairing on the Kinetics of Proton Transfer to the Hydride Cluster [W₃S₄H₃(dmpe)₃]⁺