Synthesis, structure, and NO-donor activity of bis(5-nitropyridine-2-thiolato)tetranitrosyliron

A new method is developed for the synthesis of the binuclear iron tetranitrosyl complex with 5-nitropyridine-2-thiolate, [Fe2(SC5H3N2O2)2(NO)4] (I), from 2,2’-dithiobis(5-nitropyridine) and hydrazine hydrate in an aqueous-alcohol solution followed by the replacement of the thiosulfate ligands in an aqueous solution of salt Na2[Fe2(S2O3)2(NO)4] · 4H2O 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 ΔEQ = 1.243(1) mm/s, isomeric shift δFe = 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).