Proteins provide metal ions with specialized coordination environments that enable a range of remarkable reactivity, many of which are considered highly challenging to replicate in synthetic systems. For example, metalloenzymes efficiently mediate the transformation of substrates like CO2, N2, H2, O2, and C-H bonds. Synthetic mimics of metalloproteins are useful tools to understand structure-function relationships, as well as for enriching abiotic systems with bioinspired properties. However, the primary coordination spheres within metalloproteins have several essential and interrelated attributes that have been difficult to simultaneously recapitulate in model systems. In natural systems, weak-field ligands like carboxylates, water, and imidazoles promote unique reactivity associated with high-spin electronic states. Although these ligands are intrinsically labile, bulky protein scaffolds chelate and site-isolate the metal center(s). Immobilization of the site prevents shuffling or aggregation that would otherwise occur in a small molecule system. Furthermore, ligands coordinating through carboxylates (from Asp, Glu, and the C-terminus of proteins) have variable denticity, bridging modes, and geometries that are often influenced by secondary sphere hydrogen-bonding interactions from residues near the metal site.