Iron-sulfur enzymes are ubiquitous in biology and are used to store, redistribute, and donate electrons. Consequently, iron-sulfur clusters are primary components in electron transfer chains and act as catalytic centers for small molecule reactivity. The structural plasticity of these clusters enables their facile interconversion between many cluster nuclearities and topologies. Notably, several metalloenzyme cofactors feature heterometals bound to iron-sulfur clusters, such as in nitrogenases (V, Fe, and Mo), carbon monoxide dehydrogenase (CODH, Ni) and acetyl coenzyme synthase (ACS, Ni). Several of these cluster topologies are unprecedented in synthetic iron-sulfur clusters and often feature low-coordinate metal sites that are the proposed substrate binding sites. In our efforts to synthesize biomimetic analogues of the Ni-dependent C and A clusters, we explore the reductive insertion of low-valent metals into iron-sulfur clusters. These reactions give new [M-4Fe-4S] clusters with a face-capped tetrahedral metal site (M = Mn, Fe, Co, Ni). Analysis of the structural data in combination with SQUID magnetometry, EPR, and Mössbauer spectroscopy reveals the metal oxidation states and the spin-coupling scheme across these clusters. These give insight into the potential electronic structure determinants of cofactor reactivity.