Chalcogenide chemistry in ionic liquids: nonlinear optical wave-mixing properties of the double-cubane compound [Sb7S8Br2](AlCl4)3.

The new cation [Sb(7)S(8)Br(2)](3+) has a double-cubane structure and forms as the [AlCl(4)](-) salt from the ionic liquid EMIMBr-AlCl(3) (EMIM = 1-ethyl-3-methylimidazolium) at 165 degrees C. The compound is noncentrosymmetric with space group P2(1)2(1)2(1) and exhibits second-harmonic and difference-frequency nonlinear optical response across a wide range of the visible and near-infrared regions.