Carbon monoxide ligation at single metal atom sites in a 2D manganese-cobalt coordination network: equilibrium at room temperature

We find that CO ligates selectively to nitrogen tetra-coordinated Co(i) single metal atom sites at room temperature in a manganese–cobalt bi-metallic coordination network self-assembled on graphene. The bound state is metastable, determined by pressure-dependent equilibrium conditions between adsorption and desorption, with an upright, end-on bonding geometry (binding energy 0.73 eV). The ligand vibrational hot-band can be populated due to the weak coupling with the substrate. The CO uptake/saturation curve is modeled using Temkin and Hill isotherms, unveiling network-mediated anti-cooperative adsorption. While contributions from direct dipole–dipole interactions and Förster energy transfer are ruled out, the observed anti-cooperativity originates from network-mediated electronic and magnetic effects. Our findings provide direct insight into ligand dynamics at single metal atom sites in 2D materials and suggest tunable reactivity properties of a 2D biomimetic functional material through its tailored design.