Roussin's black salt

Roussin's Black Salt, also known as ammonium iron sulfide, is a chemical compound with the formula (NH4)2[Fe4S3(NO)]2. This compound is notable for its deep black color and its historical significance in the study of nitrosyl complexes. Roussin's Black Salt is named after the French chemist Edmond Frémy's student, Roussin, who first described it in the 19th century. The compound is an example of a transition metal sulfide and is of interest both for its unique chemical properties and for its role in the development of coordination chemistry.

Properties and Structure

Roussin's Black Salt is characterized by its intense black color and solid state at room temperature. The compound's structure consists of a complex anion, [Fe4S3(NO)]2−, where four iron atoms are covalently bonded to three sulfide (S2−) ions and two nitrosyl (NO) groups. This arrangement forms a cluster that is an example of a metal-sulfur cluster, a type of structure that is important in both synthetic chemistry and biochemistry.

The presence of the nitrosyl ligand, which acts as a stabilizing force within the compound, is particularly noteworthy. Nitrosyl complexes like Roussin's Black Salt are significant in the study of coordination chemistry because they help elucidate the bonding and behavior of NO, a molecule of importance in various biological and industrial processes.

Synthesis

Roussin's Black Salt can be synthesized through the reaction of iron salts with sulfide sources in the presence of nitric oxide. The synthesis typically involves the use of ammonium sulfide ((NH4)2S) and an iron(II) salt, such as iron(II) sulfate (FeSO4), under an atmosphere of nitric oxide (NO). The reaction proceeds through the formation of intermediate species, eventually yielding the black salt as a precipitate.

Applications

While Roussin's Black Salt is primarily of academic interest, studying its properties and reactions can provide insights into the behavior of similar metal-sulfur and nitrosyl complexes. These insights have implications for understanding catalytic processes, the behavior of metalloenzymes, and the industrial application of similar compounds.

Safety and Handling

As with many chemical compounds, especially those containing transition metals and sulfide ions, Roussin's Black Salt requires careful handling. The compound should be stored in a well-ventilated area, away from sources of moisture and incompatible materials. Safety data sheets (SDS) should be consulted for detailed information on handling, storage, and disposal.

See Also

• Nitrosyl complex
• Coordination chemistry
• Transition metal sulfide