Mercuric Ionic Liquids: [Cnmim][HgX3], Where n=3, 4 and X = Cl, Br

A series of mercury(II) ionic liquids, [C(n)mim][HgX3], where [C(n)mim] = n-alkyl-3-methylimidazolium with n = 3, 4 and X = Cl, Br, have been synthesized following two different synthetic approaches, and structurally characterized by means of single-crystal X-ray structure analysis ([C(3)mim][HgCl3] (1), Cc (No. 9), Z = 4, a = 16.831(4) angstrom, b = 10.7496(15) angstrom, c = 7.4661(14) angstrom, beta = 105.97(2)degrees, V = 1298.7(4) angstrom(3) at 298 K; [C(4)mim][HgCl3] (2), Cc (No. 9), Z = 4, a = 17.3178(28) angstrom, b = 10.7410(15) angstrom, c = 7.4706(14) angstrom, beta = 105.590(13)degrees, V = 1338.5(4) angstrom(3) at 170 K; [C(3)mim][HgBr3] (3), P2(1/c) (No. 14), Z = 4, a = 10.2041(10) angstrom, b =10.7332(13) angstrom, c = 14.5796(16) angstrom, beta = 122.47(2)degrees, V = 1347.2(3) angstrom(3) at 170 K; [C(4)mim][HgBr3] (4), Cc (No. 9), Z = 4, a = 17.093(3) angstrom, b = 11.0498(14) angstrom, c = 7.8656(12) angstrom, beta = 106953(13)degrees, V = 1421.1(4) angstrom(3) at 170 K). Compounds 1, 2, and 4 are isostructural and are characterized by strongly elongated trigonal [HgX5] bipyramids, which are connected via common edges in chains. In contrast, 3 contains [Hg2Br6] units formed by two edge-sharing tetrahedra. With melting points of 69.3 degrees C (1), 93.9 degrees C (2), 39.5 degrees C (3), and 58.3 degrees C (4), all compounds qualify as ionic liquids. 1, 2, and 4 solidify upon fast cooling as glasses, whereas 3 crystallizes. Cyclic voltammetry shows two separate, quasi-reversible redox processes, which can be associated with the 2Hg(2+)/Hg-2(2+) and Hg-2(2+)/2Hg redox couples.