- Na[B(hfip)4] (hfip = OC(H)(CF3)2): A weakly coordinating anion salt and its first application to prepare ionic liquids
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The fast, high yield synthesis and full characterization of Na[B(hfip) 4] (hfip: OC(H)(CF3)2) from NaBH4 and hexafluoroisopropanol (hfipH) is presented. By anion metathesis, five [B(hfip)4]- salts with classical/functionalized ionic liquid (IL) cations with melting points between 0 ([C6MIM] +[B(hfip)4]-) and 113 °C ([C 4MMorph]+[B(hfip)4]-) were prepared. Four of these qualify as ILs and one as room temperature IL (RTIL). The properties of the borate anion [B(hfip)4]- and its aluminum analogue [Al(hfip)4]- were compared based on the available structural information from XRD. Viscosities (10.3 (90 °C) to 855 (0 °C) mPa s-1) and conductivities (0.603 (30 °C) to 4.844 (90 °C) mS cm-1) were measured between 0 and 90 °C, and described by the Vogel-Fulcher-Tammann (VFT) equations. The properties of the [B(hfip)4]- ILs were analyzed in the context of the anion-dependent molecular volume Vm-viscosity-/conductivity- correlations, also in comparison to ILs with [BF4] -/[PF6]-, [N(CN)2]-, [Tf2N]- and [Al(hfip)4]- counterions. The viscosities and conductivities of [B(hfip)4] - ILs are slightly inferior to [Al(hfip)4]- ILs, similar to/better than all other anions given above. According to the Walden plots, the ionicity of the [B(hfip)4]- ILs may at least be classified as "good". By sharp contrast to the [Al(hfip) 4]- ILs, the [B(hfip)4]- ILs have good stability against humidity/water. Thus, handling of [B(hfip) 4]- ILs in an open laboratory atmosphere over hours and days is allowed and further facilitates the use of this new IL class. The Royal Society of Chemistry 2011.
- Bulut, Safak,Klose, Petra,Krossing, Ingo
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- The synthesis of a new family of boron-based anion receptors and the study of their effect on ion pair dissociation and conductivity of lithium salts in nonaqueous solutions
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A new family of anion receptors based on boron compounds has been synthesized. These compounds can be used as anion receptors in lithium battery electrolytes. This family includes various borane and borate compounds with different fluorinated aryl and fluorinated alkyl groups. When these anion receptors are used as additives in 1,2-dimethoxyethane (DME) solutions containing various lithium salts, the ionic conductivities of these solutions are greatly increased. The electrolytes tested in this study were DME solutions containing the following lithium salts: LiF, LiCl, LiBr, LiI, CF3COOLi, and C2F5COOLi. Without the additive, the solubility of LiF in DME (and all other nonaqueous solvents) is very low. With some of these boron compounds as additives, LiF solutions in DME with concentration as high as 1 M were obtained. The solubilities of the other salts were also increased by these additives. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy studies show that Cl- and I- anions are complexed with these compounds in DME solutions containing LiCl or LiI salts. The degree of complexation is also closely related to the structures of the fluorinated aryl and alkyl groups, which act as electron-withdrawing groups. The NEXAFS results are in good agreement with ionic conductivity studies.
- Lee,Yang,Xiang,McBreen,Choi
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p. 2813 - 2818
(2008/10/08)
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