Designing ionic liquids with boron cluster anions: Alkylpyridinium and imidazolium [nido-C2B9H11] and [closo-CB11H12] carborane salts

A range of new alkylpyridinium and imidazolium carborane salts with [nido-C2B9H12]−, [closo-CB11H12]−, and [RC2B11H11]− (R = methyl or butyl) anions have been prepared and characterized by physical and thermal methods, including the solid state structures of five of the salts determined by single crystal X-ray diffraction. The tendency of the salts to form low-melting ionic liquids has been assessed; all the salts studied with [nido-C2B9H12]− anions melted below 100 °C and, significantly, have melting points that are 25–85 °C lower than those of the corresponding [closo-CB11H12]− analogs, demonstrating that a wider range of boron-rich ionic liquid materials can be readily accessed. © 2008 The Royal Society of Chemistry