Roussin's black salt

Roussin's black salt is a chemical compound with the formula KFe₄S₃(NO)₇.^[1] It consists of the potassium salt of the [Fe₄S₃(NO)₇]⁻ anion, metal nitrosyl compound. First described by Zacharie Roussin in 1858,^[2] it is one of the first synthetic iron-sulfur clusters along with the red salt also bearing his name.

Roussin's black salt

Names
Other names potassium heptanitrosyltri-μ3-thiotetraferrate
Identifiers
CAS Number	12518-87-5 (potassium salt) Y 12518-87-5 (anion) N 54724-04-8 (ammonium salt) N 83017-31-6 (sodium salt) N
3D model (JSmol)	Interactive image
PubChem CID	119057276
InChI InChI=1S/4Fe.K.7NO.3S/c;;;;;7*1-2;;;/q4*-2;8*+1;;; Key: HCASECMHPPKIPY-UHFFFAOYSA-N
SMILES [K+].[Fe-3]12([N+]#[O+])S3[Fe-4]([N+]#[O+])([N+]#[O+])S1[Fe-4]([N+]#[O+])([N+]#[O+])S2[Fe-4]3([N+]#[O+])[N+]#[O+]
Properties
Chemical formula	Fe4KN7O7S3
Molar mass	568.70 g·mol−1
Appearance	Black solid
Melting point	198 to 200 °C (388 to 392 °F; 471 to 473 K)
Related compounds
Related	Roussin's Red Salt
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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.^[3]

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.^[4] 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.^[5] Also, Roussin’s Black Salt exhibits antibacterial activity in some food processing applications.^[6]

See also

• Roussin's red salt

References

1. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 1094. ISBN 978-0-08-037941-8.
2. Butler, Anthony R. (July 1982). "The chemist Z. Roussin (1827-94)". Journal of Chemical Education. 59 (7): 549. Bibcode:1982JChEd..59..549B. doi:10.1021/ed059p549.
3. Jaworska, Maria; Stasicka, Zofia (March 2006). "Structure and UV–vis spectroscopy of roussin black salt [Fe4S3(NO)7]−". Journal of Molecular Structure. 785 (1–3): 68–75. Bibcode:2006JMoSt.785...68J. doi:10.1016/j.molstruc.2005.09.030.
4. Marchlewski, L.; Sachs, J. (1892). "Studien über ROUSINS Salz". Zeitschrift für anorganische Chemie. 2 (1): 175–181. doi:10.1002/zaac.18920020117.
5. Janczyk, Agnieszka; Wolnicka-Glubisz, Agnieszka; Chmura, Antonina; Elas, Martyna; Matuszak, Zenon; Stochel, Grazyna; Urbanska, Krystyna (February 2004). "NO-dependent phototoxicity of Roussin's black salt against cancer cells". Nitric Oxide. 10 (1): 42–50. doi:10.1016/j.niox.2004.01.009. PMID 15050534.
6. Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 1094–1095. ISBN 978-0-08-037941-8.