Designing ionic liquids with boroncluster anions: alkylpyridinium and imidazolium [nido-C2B9H11] and [closo-CB11H12] carborane salts

Abstract

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.