Iron-sulfur-nitrosyl complexes salts

The isolation of [Fe2(SMe)2(NO)4] from certain preserved vegetables and its implication in diet-related carcinogenesis, underlines the similarities between the iron- sulfur nitrosyl systems and the complexes discussed above. The proto-typic iron-sulfur nitrosyl complexes are Roussin s salts (Section Nitric Oxide Complexes with Sulfur Donors ). [Fe2 (SR)2 (N0)4] complexes are known with a wide range of R groups. They can be synthesized directly from iron(ll) salts, as shown in equation (20), or a variety of other mononuclear iron complex precursors including [Fe(NO)(S2CNMe2)2] (with excess RS ), [Fe(CO)3NO], and [Fe(NO)2(SR)2] . 

Roussin s red and black salts were among the earhest synthesized nitrosyl complexes. These iron-sulfur nitrosyls were discovered by Roussin while studying the action of sulfur on solutions of sodium nitroprusside and described in 1858 [42]. 

Roussin s red salt, K2[Fe2S2(NO)4] is a historically important complex of a great interest for biochemists, being the first synthetic model of iron-sulfur cluster, analogical to those present widely in proteins (vide infra). Moreover, it is already a nitrosylated form of such a cluster, and the cluster nitrosylation just recently has been widely studied, since this process is associated with the regulatory action of many non-heme iron-sulfur enzymes. 

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