The free primary hydroxyl groups in the metal-organic framework of CDMOF-2, an extended cubic structure containing units of six gamma-cyclodextrin tori linked together in cube-like fashion by rubidium ions, has been shown to react with gaseous CO2 to form alkyl carbonate functions. The dynamic covalent carbon-oxygen bond, associated with this chemisorption process, releases CO2 at low activation energies. As a result of this dynamic covalent chemistry going on inside a metal-organic framework, CO2 can be detected selectively in the atmosphere by electrochemical impedance spectroscopy. The "as-synthesized" CDMOF-2 which exhibits high proton conductivity in pore-filling methanolic media, displays a similar to 550-fold decrease in its ionic conductivity on binding CO2. This fundamental property has been exploited to create a sensor capable of measuring CO2 concentrations quantitatively even in the presence of ambient oxygen.