Ionic liquids (ILs), especially task-specific ILs, are capable of dissolving various solids at moderate temperatures without the need for special reaction vessels. Direct synthesis of binary sulfides of B, Bi, Ge, Mo, Cu, Au, Sn, In, Ti, V, Fe, Co, Ga, Ni, Al, Zn, and Sb in [P66614]Cl was tested at 100 °C, i.e. below the melting point of sulfur. Under these conditions, substantial sulfide formation occurred only for nickel (Ni3S4, Ni3S2, NiS) and copper (Cu2S, CuS). Sb showed no formation of crystalline sulfide, but after addition of EtOH, an orange material precipitated which was identified as amorphous metastibnite. Subsequently, the dissolution of antimony sulfide (Sb2S3), the main source of antimony production, in the phosphonium-based ILs [P66614][OAc] and [P66614]Cl at 100 °C was studied in detail. The dissolution proceeds without H2S evolution, and amorphous Sb2S3 can be precipitated from these solutions. Heating Sb2S3 in the Lewis-acidic IL [BMIm]Cl·4.7AlCl3 led to the crystallization of [Sb13S16Cl2][AlCl4]5, which contains a new quadruple heterocubane cation.