Computational and Experimental Studies on the Adsorption of CO, N<sub>2</sub>, and CO<sub>2</sub> on Mg-MOF-74

Adsorption of carbon monoxide, dinitrogen, and carbon dioxide on the porous metal−organic framework Mg-MOF-74 was investigated by means of a combined methodology comprising variable-temperature infrared spectroscopy and ab initio periodic DFT-D calculations using the CRYSTAL code. Both CO and N<sub>2</sub> were found to form nearly linear (Mg<sup>2+</sup>···CO and Mg<sup>2+</sup>···NN) adsorption complexes, in contrast with CO<sub>2</sub>, which forms an angular Mg<sup>2+</sup>···OCO complex. From IR spectra recorded at a variable-temperature, the standard adsorption enthalpy (Δ<i>H</i><sup>0</sup>) was found to be −29, −21, and −47 kJ mol<sup>−1</sup> for CO, N<sub>2</sub>, and CO<sub>2</sub>, respectively. Calculated values of Δ<i>H</i><sup>0</sup>, including an empirical correction for dispersion forces, resulted to be in a reasonably good agreement with those experimentally obtained. Calculations also showed the very significant role played by dispersion forces, which account for about one-half of the adsorption enthalpy for each of the three adsorbates, CO, N<sub>2</sub>, and CO<sub>2</sub>. The results are discussed in the broader context of the adsorption of the same gases on other MOFs and also on zeolites.