Gold Compounds as Ionic Liquids. Synthesis, Structures, and Thermal Properties of N,N‘-Dialkylimidazolium Tetrachloroaurate Salts

The salts [C₆H₁₁N₂][AuCl₄] (1) and [C₈H₁₅N₂][AuCl₄] (2) ([C₆H₁₁N₂]⁺ = 1-ethyl-3-methylimidazolium; [C₈H₁₅N₂]⁺ = 1-butyl-3-methylimidazolium), prepared by a solvent-free method, display similar crystal structures. 1 crystallizes in the monoclinic P2₁/c space group (a = 11.1915(15) Å, b = 12.380(2) Å, c = 9.2883(13) Å; β = 98.810(16)°; Z = 4) and 2 in the triclinic P1̄ space group (a = 7.9354(14) Å, b = 8.3930(15) Å, c = 11.397(2) Å; α = 83.94(2)°, β = 87.93(2)°, γ = 78.04(2)°; Z = 2). In both cases, a unique motif is seen consisting of linear chains of alternating corner-to-face arranged [AuCl₄]^- ions at Au···Cl separations of 3.356(3) Å (1) and 3.452(3) Å (2). Ionic liquid behavior is observed from 58 to 220 °C for 1 and 50 to 250 °C for 2.