The study investigates the cooperative insertion of CO₂ into metal–amine bonds in diamine-appended metal-organic frameworks (MOFs), leading to step-shaped CO₂ adsorption isotherms. The mechanism involves the insertion of CO₂ molecules into metal–amine bonds, causing a reorganization of the amines into well-ordered chains of ammonium carbamate. This results in large CO₂ separation capacities with small temperature swings and lower regeneration energies compared to aqueous amine solutions. The findings provide a framework for designing efficient adsorbents for CO₂ capture and offer insights into the conservation of Mg²⁺ in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco).The study investigates the cooperative insertion of CO₂ into metal–amine bonds in diamine-appended metal-organic frameworks (MOFs), leading to step-shaped CO₂ adsorption isotherms. The mechanism involves the insertion of CO₂ molecules into metal–amine bonds, causing a reorganization of the amines into well-ordered chains of ammonium carbamate. This results in large CO₂ separation capacities with small temperature swings and lower regeneration energies compared to aqueous amine solutions. The findings provide a framework for designing efficient adsorbents for CO₂ capture and offer insights into the conservation of Mg²⁺ in ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco).