In nature, the anaerobic CO dehydrogenase (CODH) enyzmes interconvert CO2 and CO with high rates and selectivity that are an inspiration for chemists interested in catalytic reduction of CO2. The active site for CODH is an unusual iron-sulfur cluster with a nickel atom inserted into the cluster. Crystallographic models suggested that the nickel site was three-coordinate, but there were no examples of three-coordinate nickel in synthetic iron-sulfur clusters until we prepared the first examples. We examined these novel clusters in detail using crystallography, spectroscopy, and magnetism with complementary DFT calculations to elucidate the electronic structures. There is no evidence that nickel(0) is accessible in these clusters; however, nickel(I) can have metal-metal bonds that store extra electrons. The clusters can bind CODH inhibitors, and the products are analyzed using ENDOR spectroscopy. These results help to understand the structure-function relationships that govern multimetallic clusters for catalytic CO2 reduction.