Na[B(hfip)4] (hfip = OC(H)(CF3)2): a weakly coordinating anion salt and its first application to prepare ionic liquids.

The fast, high yield synthesis and full characterization of Na[B(hfip)(4)] (hfip: OC(H)(CF(3))(2)) from NaBH(4) 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 (C(6)MIMB(hfip)(4)) and 113 °C (C(4)MMorphB(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 V(m)-viscosity-/conductivity-correlations, also in comparison to ILs with BF(4)/PF(6), N(CN)(2), Tf(2)N 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.