Antimony pentasulfide is an inorganic compound of antimony and sulfur, also known as antimony red. It is a nonstoichiometric compound with a variable composition. Its exact structure is unknown. Commercial samples are usually contaminated with sulfur, which may be removed by washing with carbon disulfide in a Soxhlet extractor.
Antimony pentasulfide can be produced by the reaction of antimony with sulfur at a temperature between 250-400 °C in an inert atmosphere.
It may be used as a red pigment and is one possible precursor to Schlippe's Salt, Na3SbS4, which can be prepared according to the equation:
Like many sulfides, this compound liberates hydrogen sulfide upon treatment with strong acids like hydrochloric acid.
Analysis by Mössbauer spectroscopy indicates that this compound is a derivative antimony(III), explaining the production of antimony(III) chloride, rather than antimony(V) chloride, upon acidification. It is therefore not analogous to the phosphorus(V) compound phosphorus pentasulfide.