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This paper describes selected thermophysical properties of the newly obtained paramagnetic inky. opaque ionic liquid. 1-butyl-3-methylimidazolium tetraisothiocyanato-cobaltate(II) ((BMlm) 2 (Co(NCS) 4 ]). Some properties of the homologous ionic liquid (IL), 1-ethyl-3-methylimidazolium tetraisothiocyanato-cobaltate(II) ((EMIm) 2 [Co(NCS) 4 ]), have been presented earlier and are discussed here together with those for (BMIm) 2 [(Co(NCS) 4 ]. On the basis of experimental densities, kinematic viscosities, conductivities, and surface tensions, some additional parameters have been determined, i.e., expansivity coefficients and surface thermodynamic properties. The influence of structural variation in the 1-alkyl-3-methylimidazolium cation is also discussed.

Activity coefficients at infinite dilution, γi∞, 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), (C4MIm)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 γi∞ of solutes in the paramagnetic ionic liquid (C4MIm)2[CoBr4] have been compared at 298 K with results of γi∞ 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 =...