Roussin's black salt explained

Roussin's black salt is a chemical compound with the formula KFe₄S₃(NO)₇. It consists of the potassium salt of the [Fe₄S₃(NO)₇]⁻ anion, metal nitrosyl compound. First described by Zacharie Roussin in 1858,^[1] it is one of the first synthetic iron-sulfur clusters along with the red salt also bearing his name.

Structure

The cluster anion has the geometry of an incomplete cubane-type cluster with C_3v symmetry. The dark colour of the complex is attributed to a number of charge-transfer interactions.^[2] thumb|left|Structure of the hydrated ammonium salt of [Fe₄S₃(NO)₇]⁻.

Synthesis

Roussin’s black salt is produced by the reaction of nitrous acid, potassium hydroxide, potassium sulfide, and iron(II) sulfate in aqueous solution.^[3] It can also be formed by the conversion of Roussin's red salt in mildly acidic conditions. This reaction is reversible and Roussin’s red salt is reformed upon alkalization of the reaction solution.

Uses

Roussin’s black salt is a nitric oxide donor.^[4] Also, Roussin’s Black Salt exhibits antibacterial activity in some food processing applications.

See also

• Roussin's red salt

Notes and References

1. Butler. Anthony R.. The chemist Z. Roussin (1827-94). Journal of Chemical Education. July 1982. 59. 7. 549. 10.1021/ed059p549. 1982JChEd..59..549B.
2. Jaworska. Maria. Stasicka. Zofia. Structure and UV–vis spectroscopy of roussin black salt [Fe4S3(NO)7]−. Journal of Molecular Structure. March 2006. 785. 1–3. 68–75. 10.1016/j.molstruc.2005.09.030. 2006JMoSt.785...68J.
3. Marchlewski. L.. Sachs. J.. Studien über ROUSINS Salz. Zeitschrift für anorganische Chemie. 1892. 2. 1. 175–181. 10.1002/zaac.18920020117.
4. Janczyk. Agnieszka. Wolnicka-Glubisz. Agnieszka. Chmura. Antonina. Elas. Martyna. Matuszak. Zenon. Stochel. Grazyna. Urbanska. Krystyna. NO-dependent phototoxicity of Roussin's black salt against cancer cells. Nitric Oxide. February 2004. 10. 1. 42–50. 10.1016/j.niox.2004.01.009. 15050534.