Breaking Scaling Relationships in CO2 Electroreduction with Isoelectronic Analogs [Fe4N(CO)12]- and [Fe3MnO(CO)12]-

[Fe4N(CO)(12)](-) and [Fe3MnO(CO)(12)](-) have the same total electron count and overall charge, as well as similar reduction potentials of -1.21 and -1.17 V vs SCE in MeCN, respectively. Both clusters form the reduced hydride upon single electron transfer (ET) and proton transfer (PT). It is known that [Fe4N(CO)(12)](-) is an electrocatalyst for selective CO2 reduction to formate at -1.2 V vs SCE in either pH 7 buffered water or in MeCN/H2O (95:5) and an effective electrocatalyst for H+ reduction to H-2 under N-2 under the same conditions. In contrast, [Fe3MnO(CO) (12)]affords no products upon electrolysis, beyond [H-Fe3MnO(CO)(12)](-). We determine that [H-Fe3MnO(CO)(12)](-) is a weaker hydride donor than [H-Fe4N(CO)(12)](-) by about 4 kcal mol(-1), and this is a breaking of the hydricity versus reduction potential scaling relationship previously established for a series of metal carbonyl clusters electrocatalysts.