ENigM proposes a family of evolutionary mimics of nitrogenase cofactor FeMo-co, for the understanding of the structure/properties relationship accounting for the exceptional reducing power of this complex structure. As a benchmark reaction, we choose the reduction of CO2, as it will enlarge and complete the information provided in the frame of N2 reduction usually considered in the field of nitrogenase mimics. This work will allow for the identification of systems able to perform the multi-electron reduction of small molecules, as the conversion of CO2 to formate, methanol or methane. The initial platform shows several structural analogies with FeMo-co: coordination sphere made of carbon and sulfur only, strongly charged carbon bridging between two iron centers. The easy modification of the ligand brings a strong modularity to our system, without the risk of denaturing the central metal-carbon interaction. A methodological ground will be established : redox and acido-basic properties of the initial platform, reactivity in the presence of CO2. This family of FeMo-co mimics will then be extended by stepwise increase of the number of metallic centers, while studying the properties of the obtained clusters.