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Reduction of neutral binuclear nitrosyl iron complexes of ''m-S'' structural type [Fe 2 (SR) 2 (NO) 4 ] with R = 3-nitro-phenol-2-yl, 4-nitro-phenol-2-yl, 5-nitropyridine-2-yl and pyridine-2-yl in aprotic solution has been studied by a cyclic voltammetry (CVA) method at a wide range of potential scan rates.A complex with R = 3-nitro-phenol-2-yl was synthesized for the first time; therefore it was studied by X-ray and Mo ¨ssbauer spectroscopy. The parameters of the Mo ¨ssbauer spectrum are: isomer shift d Fe = 0.115(1) mm s À1 , quadrupole splitting DE Q = 1.171(1) mm s À1 , and line width = 0.241(1) mm s À1 at 85 K. From the current-voltage curve, the transfer of the first electron was found to be reversible, and the redox-potentials of these reactions were determined. The further reduction of the complexes was determined to be irreversible because the product of the second electron addition is instable and decomposes partially during the potential scan. Calculations of geometric and electronic structures of monoanions and dianions of the complexes under study and their theoretical redox-potentials were performed by DFT methods. Introduction of the electron-acceptor NO 2 group into the phenyl and pyridine rings of sulfur-containing ligands of the nitrosyl iron complexes was found to affect the geometry of the anions and the distribution of the additional negative charge, as well as to increase the redox-potential and to facilitate reduction of these complexes.

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A new method is developed for the synthesis of the binuclear iron tetranitrosyl complex with 5 nitropyridine 2 thiolate, [Fe 2 (SC 5 H 3 N 2 O 2 ) 2 (NO) 4 ] (I), from 2,2' dithiobis(5 nitropyridine) and hydra zine hydrate in an aqueous alcohol solution followed by the replacement of the thiosulfate ligands in an aque ous solution of salt Na 2 [Fe 2 (S 2 O 3 ) 2 (NO) 4 ] ⋅ 4H 2 O by functional 5 nitropyridine 2 thiolates. It is established by the X ray diffraction method that the complex has the structure of the μ SR type and crystallizes as two polymorphs. The Moessbauer spectral parameters at 293 K (quadrupole splitting ΔE Q = 1.243(1) mm/s, iso meric shift δ Fe = 0.095(1) mm/s, and absorption line width Γ = 0.263(1) mm/s) for studied compound I are similar to the isoelectronic complexes with thiophenoxide, pyridyl 2 thiolate, and pyrimidyl 2 thiolate. According to the electrochemical analysis data, complex I is a more efficient donor of NO in hydrolytic decomposition in protic media with NO formation than its isostructural analog with the unsubstituted pyridylthiolate ligand. The maximum amount of NO generated by complex I in a 1% aqueous solution of dimethyl sulfoxide at T = 25°C and pH 7.0 is 7.4 nmoles and increases twofold with an increase in the acidity of the medium (to pH 6.5) or temperature (37°C).