Tetrahalidometallate(II) Ionic Liquids with More than One Metal: The Effect of Bromide versus Chloride.

Fifteen N-butylpyridinium salts - five monometallic [C 4 Py] 2 [MBr 4 ] and ten bimetallic [C 4 Py] 2 [M 0.5 a M 0.5 b Br 4 ] (M=Co, Cu, Mn, Ni, Zn) - were synthesized, and their structures and thermal and electrochemical properties were studied. All the compounds are ionic liquids (ILs) with melting points between 64 and 101 °C. Powder and single-crystal X-ray diffraction show that all ILs are isostructural. The electrochemical stability windows of the ILs are between 2 and 3 V. The conductivities at room temperature are between 10 -5 and 10 -6  S cm -1 . At elevated temperatures, the conductivities reach up to 10 -4  S cm -1 at 70 °C. The structures and properties of the current bromide-based ILs were also compared with those of previous examples using chloride ligands, which illustrated differences and similarities between the two groups of ILs.