Predicted geometry DFT calculations are used to resolve the most stable configuration in the ground state. For CO, we find a perpendicular orientation of the pyrazines upon adsorption of 1 molecule per f.u. while for 1.5 and 2 CO per f.u. a parallel orientation is predicted. The energy differences between the two configurations are 0.029 eV, 0.007 eV, and 0.119 eV, respectively, per formula unit. Therefore, for the predicted saturation loading of 2 CO per f.u., the parallel orientation of the pyrazine ring is the most stable. This is consistent with the neutron diffraction patterns of CO-loaded Fe(d4-pz)[Pt(CN)4]. For 1.5 and 2 CO per f.u., the two binding sites obtained in our calculations agree with neutron diffraction: on-top of the open-metal site (site A), and between the pyrazine rings (site B). The occupancy of site B is 0.5 for 1.5 CO per f.u. and 1.0 for 2 CO per f.u. The A site is always fully occupied. The CO molecules are oriented perpendicular to the pyrazine planes and parallel to the Pt[CN]4 plane (see Figure ), regardless of the amount of gas. The unit cell presents a monoclinic distortion (γ = 89.55 • ), in agreement with the neutron diffraction results. In the case of CO2, the orientation of the pyrazines is parallel for 1 and 1.5 CO2 per f.u. with a corresponding energy difference between parallel and perpendicular of 0.016 and 0.036 eV per f.u., respectively. Only the parallel configuration could be converged for 2 molecules suggesting that large interatomic forces could prevent a perpendicular configuration in this case. For a loading of 1 CO2 per f.u. the molecules are located only on site A and are perpendicular to the pyrazine planes. When 1.5 and 2 molecules per f.u. are considered, CO2 locates in both sites A and B. The molecules in site A are again perpendicular to the pyrazine planes, while the molecules in site B are almost parallel to the pyrazine planes and perpendicular to the neighbouring CO2 (Figure ). While molecules in site B are parallel to the Pt(CN)4 plane for a loading of 1.5 CO2, for a 2 molecule-loading, the CO2 the are tilted off-plane. In the first case, the molecules on-top of the platinum in site A move slightly off the metal position (see Figure ). Also in this case, the structure is monoclinically distorted (γ = 89.51 • ), consistent with the neutron diffraction results. Amount of gas adsorbed. Neutron diffraction on the deuterated compound suggests that most of the pyrazines are in parallel orientation for both the CO-and CO2-loaded materials. DFT confirms that this configuration only occurs when 1.5 or 2 molecules of CO are adsorbed per openmetal-site. Therefore, we can deduce that more than one molecule has been adsorbed. Since adsorption isotherms are not available for CO, we estimate the saturation loading at about 2 CO mol / Fe mol from kinetic uptake experiments which are in agreement with our neutron diffraction results. The combination of INS and DFT calculations is consistent with this loading value. In the case of CO2, a parallel configuration is predicted by DFT for all the loading values considered. We have retained the value of 1.5 molecules per f.u. in our calculations, which is consistent with the saturation loading for CO2 determined experimentally from adsorption isotherms (about 1.5 mol of CO2 per Fe mol ), and with the refined value of ca. 1.7 obtained