The concept of outer-sphere coordination (OSC) is surveyed in the context of bioinorganic chemistry. A distinction is made between electronic and structural OSC, both arising from the interaction of the protein matrix with inner sphere ligands. Electronic OSC entails the electronic interaction between the polypeptide and inner-sphere ligands. These effects principally arise from hydrogen-bonding interactions, though through-space dipolar interactions are also encountered. Structural OSC comprises primarily steric effects that do not necessarily impact ligand electronics but rather influence inner sphere topology. Additionally, the protein matrix can be envisioned as a local "solvent" whose bulk dielectric and point charges influence the metal center. Recurring themes are highlighted where OSC regulates the properties of various metalloproteins distinguished by cofactors and/or function. Finally, cases are presented where OSC has guided molecular design. © 2011 Springer Verlag Berlin Heidelberg.
Lancaster, K. M. (2012). Biological outer-sphere coordination. Structure and Bonding, 142, 119–154. https://doi.org/10.1007/430_2011_49