Decomposition of the binuclear nitrosyl iron complex with thiosulfato ligands in aqueous solutions: Experimental and theoretical study

[Display omitted] •Thiosulfato NIC undergoes intramolecular isomerization during anaerobic decay.•Thiosulfato ligand of NIC is able to coordinate on the iron atom.•Paramagnetic mononuclear NICs are formed from NICs with thiosulphato ligands on air. In this work, transformations of the anionic binuclear tetranitrosyl iron complex with thiosulfato ligands (Na2[Fe2(S2O3)2(NO)4]·4H2O) (1) have been studied in aqueous anaerobic and aerobic solutions. Under anaerobic conditions, complex 1 was shown to undergo intramolecular isomerization, in addition to NO generation, due to embedding of the oxygen atom of the thiosulfato ligand in the Fe-S bonds. The complex becomes more stable, so its further transformation, including NO release, is unlikely. The model for the complex decomposition has been suggested, and reaction rate constants have been calculated using the kinetic modeling method. As follows from the experimental data, under aerobic conditions, complex 1 is oxidized and becomes a more effective NO donor. Due to the incorporation of the oxygen atom into the Fe-S bonds, mononuclear nitrosyl intermediates are formed, which have a typical EPR signal (g = 2.03).