<p>A new analog of the active site of mononuclear dinitrosyl [1Fe–2S] proteins, [C<sub>3</sub>N<sub>2</sub>H<sub>8</sub>SFe(NO)<sub>2</sub>Cl][Fe(NO)<sub>2</sub>(C<sub>3</sub>N<sub>2</sub>H<sub>8</sub>S)<sub>2</sub>]<sup>+</sup>Cl<sup>−</sup> (<b>I</b>), has been synthesized by reacting NO with an aqueous mixture of iron(II) sulfate and N-ethylthiourea in acidic medium. The structure and properties of the complex were studied by X-ray diffraction, IR, Mössbauer, and EPR spectroscopy, in addition to quantum chemical calculations. Complex <b>I</b> spontaneously generates NO in protic media. The cytotoxicity of <b>I</b> was investigated against human cervical carcinoma (HeLa), breast cancer (MCF7), and non-immortalized (FetMCS) cell lines. The cytotoxicity of <b>I</b> against HeLa is similar to that of anticancer agents currently used clinically (platinum complexes), but <b>I</b> is 10 times less toxic in normal cells. The cytotoxicity of MCF7 cells to <b>I</b> is low.</p