Paramagnetic Ionic Liquid 1-Butyl-3-methylimidazolium Tetrabromidocobaltate(II): Activity Coefficients at Infinite Dilution of Organic Solutes and Crystal Structure

Activity coefficients at infinite dilution, γ∞ i, of different solutes (alkanes, alkenes, and alkylbenzenes as well as of the linear C1-C6 alcohols) in the paramagnetic ionic liquid 1-butyl-3-methylimidazolium tetrabromidocobaltate(II), (C 4MIm)2[CoBr4], have been determined by gas chromatography using the ionic liquid as the stationary phase. The measurements were carried out at different temperatures between (308 and 413) K. From the temperature dependence of the limiting activity coefficients, partial molar excess enthalpies at infinite dilution HiE,∞ of the solutes in the ionic liquid have been derived. Values of γ ∞i of solutes in the paramagnetic ionic liquid (C4MIm)2[CoBr4] have been compared at 298 K with results of γ∞i for ionic liquids containing the 1-butyl-3-methylimidazolium cation and different nonmagnetic anions. No significant effects caused by the paramagnetic anion have been observed. Furthermore, the single-crystal X-ray structure has been determined. It crystallizes monoclinic (C2/c), a = 16.7027(7), b = 10.3163(4), c = 15.4136(7) Å, and β = 114.246(2)°. The structure consists of isolated tetrahedral [CoBr4]2- complex anions and 1-butyl-3-methylimidazolium cations. © 2009 American Chemical Society.