Reversible dioxygen uptake at [Cu] clusters.

Dioxygen binding solely through non-covalent interactions is rare. In living systems, dioxygen transport takes place iron or copper-containing biological cofactors. Specifically, a reversible covalent interaction is established when O binds to the mono or polynuclear metal center. However, O stabilization in the absence of covalent bond formation is challenging and rarely observed. Here, we demonstrate a unique example of reversible non-covalent binding of dioxygen within the cavity of a well-defined synthetic all-Cu(i) tetracopper cluster.