Roussin's red salt

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Roussin's Red Salt
CAS number 58204-17-4
Molecular formula Fe2N4K2O4S2
Molar mass 374.04 g/mol
Appearance Dark red crystals
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Roussin’s Red Salt is the inorganic compound with the formula K2[Fe2S2(NO)4]. This metal nitrosyl was first described in 1858, making it the first synthetic iron-sulfur cluster.[1]

Structure and bonding[edit]

Roussin's red salt anion is an edge-shared bitetrahedron, wherein a pair Fe(NO)2 units are bridged by a pair of sulfide ligands. The Fe-NO bonds are linear indicating NO is acting as a three electron donor.[2] The diamagnetic compound obeys the 18-electron rule, and each iron center is assigned the oxidation state of Fe(-I).


The French chemist M. L. Roussin first prepared this salt while investigating reactions between nitroprusside ion ([Fe(CN)5NO]2−) and sulfur.[3] The salt can be prepared by the reaction of sulfide salts with iron nitrosyl halides:[4]

Fe2I2(NO)4 + 2Li2S → Li2Fe2S2(NO)4 + 2LiI

To obtain the "esters", the salt is alkylated:

Li2Fe2S2(NO)4 + 2 RX → Fe2(SR)2(NO)4 + 2 LiX

Esters can also be easily be prepared from the reaction of Fe2I2(NO)4 with the thiol.

Occurrence and potential applications[edit]

It is found in nature as its “esters" with the formula Fe2(SR)2(NO)4, where "R" is any alkyl group [1]. In addition Roussin’s red salt is discussed in the fields of microbiology and food science due to its mutagenic properties.[5]

The ester derivative are being investigated as a nitric oxide donors in biology and medicine. Due to the relatively low toxicity and good stability Roussin’s red salt. Photolysis of the compound induces the release of NO, thereby sensitizing target cells to exposure to radiation [2].

See also[edit]


  1. ^ Roussin, M. L. (1858). "Recherches sur les nitrosulfures doubles de fer (nouvelle classe de sels)". Ann. Chim. Phys. 52: 285–303. 
  2. ^ Thomas, J., Robertson, J., & Cox E. (1958). The Crystal Structure of Roussin’s Red Ethyl Ester. Acta Crystallographica, 11, 599.
  3. ^ Hans Reihlen, Adolf v. Friedolsheim (1927). "Über komplexe Stickoxydverbindungen und das sogenannte einwertige Eisen". Justus Liebigs Annalen der Chemie 457: 71. doi:10.1002/jlac.19274570103. 
  4. ^ TB Rauchfuss; TD Weatherill (1982). "Roussin's Red Salt revisited: reactivity of Fe2 (μ-E) 2 (NO) 42-(E= S, Se, Te) and related". Inorganic Chemistry 21 (2): 827–830. doi:10.1021/ic00132a071. 
  5. ^ Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.