The diamagnetic Roussin esters Fe
2(SR)
2(NO)
4 readily underwent exchange with thiols R′SH to yield Fe
2(SR′)
2(NO)
4: the exchange was faster in polar, coordinating solvents where paramagnetic, mononuclear complexes of types [Fe(NO)
2(solvent)
2]
+ and Fe(NO)
2(SR)(solvent) were formed. With the corresponding thiolate anions RS
-, the esters Fe
2(SR)
2(NO)
4 formed the mononuclear complexes [Fe(SR)
2(NO)
2]
-, which were fully characterised by EPR spectroscopy for R = H, Me, Et,
i-Pr,
t-Bu and PhCH
2: assignments of hyperfine couplings were confirmed by use of
15N. With Fe
2(SR)
2(NO)
4 and a different set of thiolate anion, R′S
-, in excess, thiol exchange occurred to give [Fe(SR′)
2(NO)
2]
-. A mechanism for formation of Fe
2(SR′)
2(NO)
4 from Fe
2(SR)
2(NO)
4 has been proposed. The paramagnetic mononuclear complexes [Fe(SR)
2(NO)
2] were also readily formed from the diamagnetic clusters [Fe
4S
3(NO)
7]
- and Fe
4S
4(NO)
4, together with [Fe(SR)
3(NO)]
-, and additionally from [Fe(CO)
3NO]
-. [Fe(SMe)
2(NO)
2]
-. was found to be a precursor of isolable Fe
2(SMe)
2(NO)
4, and [Fe(SH)
2 (NO)
2]
- to be the common precursor of both Roussin′s red anion [Fe
2S
2(NO)
4]
- and Roussin's black anion [Fe
4S
3 (NO)
7]
- interconvertible by appropriate adjustment of pH. The nitrosyl groups in these complexes were freely labile, and mononitrosyliron and dinitrosyliron fragments were readily interconvertible: FE(NO) fragments were favoured by the dimethyldithiocarbamate ligand (Me
2NCS
2) and Fe(NO)
2 fragments by thiolate ligands, RS
-, regardless of the origin of the Fe(NO)
x(
x = 1,2) fragment: both mono- and dinitrosyliron complexes persisted with [(
i-PrO)
2S
2]
- as ligand. Isotopic labelling showed the occurrence of rapid exchange of nitrogen between nitrosyl ligands and added nitrite in Fe(NO)(S
2CNMe
2)
2 and [Fe(SR)
2(NO)
2]
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