Roussin’s red salt ester

Wecksler SR, Mikhailovsky A, Korystov D, Buller F. Single- and two-photon properties of a dye-derivatized Roussin s red salt ester (Fe2( i-RS)2(NO)4) with a large TPA cross section. Inorg Chem 2007 46 395-402. 

Special attention was also paid to understanding the basic properties and reactivity patterns of the dinitrosyl iron complexes and Roussin s red salt esters, and to resolve the mechanism of their biological functions and NO emission (43-47). The quantum yield of NO release from [Fe2(p2-SR)2(NO)4] under visible light irradiation can be considerably enhanced by incorporating into the ester a proper chromophore then single- or two-photon processes were observed (46,48,49). 

Wang R, Camacho-Femandez MA et al (2009) Neutral and reduced Roussin s red salt ester [Fe2 p-RS>2(NO)4] (R = N-Pr, T-Bu, 6-Methyl-2-Pyridyl and 4,6-Dimethyl-2-Pyrimidyl) synthesis. X-ray crystal structures, spectroscopic, electrochemical and density functional theoretical investigations. Dalton Trans 777-786... 

Salts containing the anions [Fe2S2(NO)4]2 and [Fe4S3(NO)7] are often called, from their colors, Roussin s red and black salts, respectively similarly the organic derivatives [Fe2(SR)2(NO)4] are often called esters of Roussin s red salt. These names are nonsystematic and, in the case of [Fe2(SR)2(NO)4], scarcely accurate nonetheless they are convenient and they carry the sanction of long usage, and will on occasion be used here. 

Figure 3.4 Iron-sulfur nitrosyl compounds (a) Roussin s black salt and (b) Roussin s methyl red ester.

The most familiar complexes in this class are Roussin s red and black salts140 obtained as a mixture from the reaction of iron(III) sulfide with nitric oxide and an alkali metal sulfide.141 The dimeric and diamagnetic red salt, K2[Fe(NO)2S]2 gives rise to a series of stable esters [Fe(NO)2SR]2 (R = Me, Et, Ph etc.) which are also diamagnetic, dark red and soluble in organic solvents. Some preparative routes142 to the red salt and its esters are shown in Scheme 3. 

Francois-Zacharie Roussin (1827-1894) discovered the first polynuclear cluster compound of nitric oxide as a result of his study of the reactions of iron(II) sulphate, ammonium sulphide and nitrous acid (HNO2), and this black crystalline material was subsequently characterised as a salt of [Fe4S3(NO)7] (Roussin s black salt), 2. It may be converted into a red salt on treatment with alkaline, which reacts with ethyl bromide to give Roussin s red ester, [Fe2(SEt)2(NO)4], 3 [7]. 

Figure 25.6 The stnicmre of Roussin s salts (a) the ethyl ester [Fe(NO>2SEt]2 of the red salt showing pseudo-tetrahedral coordination of each iron (Fe-Fe = 272 pm), and (b) the anion of the black salt Cs[Fe4(N0)7S3].H20 showing a pyramid of 4 Fe atoms with an S atom above each of its three non-horizontal faces (Fejp —Fhast = 271 pm, Fei 5c Fcbas 357 pm). (The anion may alternatively be viewed as an FesSj ring with the chair" conformation.) Note that even the short Fe-Fc distances are appreciably greater than the Fe-Fe "single-bond distance of 250pm.

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