We demonstrate, based on experimental and theoretical evidence, that the isolated 2(CH3CN)22+ complex prepared in CH3CN and containing a mixed‐valent {Cu2II,IS} core evolves towards a new 2(CH3CN)32+ species upon solvation in CH3CN. Unlike its type III structural analogue 2(H2O)(OTf)+ active toward N2O reduction, this new type I compound is inactive. This outcome opens new perspectives for a rational for N2O activation using bio‐inspired Cu/S complexes, especially on the role of the valence localization/delocalization and the Cu−Cu bond on the reactivity. Delocalized or not delocalized? The mixed valent bis‐copper complex 2(CH3CN)22+ was isolated as a powder and has spectroscopic properties of a fully delocalized class III mixed‐valent system. Solvation in acetonitrile results in its total conversion to 2(CH3CN)32+ with this time a fully localized valence (class I). The effect on nitrous oxide reductase (N2Or) activity is discussed.