Carbon monoxide adsorbed at a low-temperature on the zeolite Li-ZSM-5 forms Li⁺ ⋯ CO and Li⁺ ⋯ (CO)₂ species characterized by C-O stretching bands at 2195 and 2187 cm^-1, respectively. These C-bonded carbonyls are in a temperature-dependent equilibrium with Li⁺ ⋯ OC and CO ⋯ Li⁺ ⋯ CO species having O-bonded CO. By means of variable-temperature FTIR spectroscopy, the enthalpy change involved in the corresponding isomerization process was found to be ΔH° = 7.8 kJ mol^-1 for the monocarbonyl and ΔH° = 5.1 kJ mol^-1 for the dicarbonyl. Therefore, although C-bonded species were always found to show a higher cation-CO interaction energy than O-bonded species, the difference is smaller in the case of dicarbonyls.