A combined experimental and quantum chemical study of CO2 adsorption in the metal–organic framework CPO-27 with different metals

Abstract

A first principles study of CO 2 adsorption is presented for a group of metal-organic frameworks (MOFs) known as CPO-27-M, where M ¼ Mg, Mn, Fe, Co, Ni, Cu, and Zn. These materials consist of onedimensional channels with a high concentration of open metal sites and have been identified as among the most promising MOFs for CO 2 capture. In addition, extensive, high-pressure, experimental adsorption results are reported for CO 2 , CH 4 , and N 2 at temperatures ranging from 278 K to 473 K. Isosteric heats of adsorption were calculated from the variable-temperature isotherms. The binding energies of CO 2 calculated using an MP2-based QM/MM method are in good agreement with those obtained from experiments. The relative CO 2 binding strengths for the different transition metals can be explained by the relative strength of electrostatic interactions caused by the effective charge of the metal atom in the direction of the open metal site induced by incomplete screening of 3d electrons. The Mn, Fe, Co, Ni, and Cu versions of CPO-27 are predicted to be anti-ferromagnetic in their ground states. Selectivities for CO 2 over CH 4 or N 2 were calculated from the experimental isotherms using ideal adsorbed solution theory.

Force-Field Development from Electronic Structure Calculations with Periodic Boundary Conditions: Applications to Gaseous Adsorption and Transport in Metal–Organic Frameworks

“…35−37 The model B Figure 8. Comparison between the experimental and simulated isotherms of CO 2 inside Zn-MOF-74 at 298 K. The experimental data of Yu et al 33 and the corresponding scaled isotherm (assume only 80% of material are accessible, which is the same value we have used for Mg-MOF-74) are shown by the closed black squares and red close circle with dashed line, respectively. The symbols are the isotherms from the GCMC simulations as predicted by the different models.…”

“…Figure 8 shows that, for Zn-MOF-74, our predicted isotherm is also in good agreement with the experimentally scaled one. 33 Given that we can obtain such a good agreement by only reparameterizing the metal−guest interactions, indicating that the parameters obtained in the Mg-MOF-74 are transferable to the Zn-MOF-74 as well as the method itself.…”

Understanding Small‐Molecule Interactions in Metal–Organic Frameworks: Coupling Experiment with Theory

“…[ 68 ] Since these studies of CO 2 adsorption in Mg 2 (dobdc), several combined experimental and theoretical approaches have been taken to identify the host-guest interactions that lead to signifi cant differences in isosteric heats among all of the metal-substituted analogs in the M 2 (dobdc) series. [ 54,69 ] Among those members, isosteric heats of adsorption ( Figure 3 ) follow a trend (Mg > Ni > Co > Fe > Mn > Zn >Cu) that unexpectedly does not correlate with the ionic radii. [ 68 ] A recent study by Yu [ 54 ] gives an explanation for the observed trend through a description of nuclear screening effects by M 2+ d-orbitals.…”

“…[ 54,69 ] Among those members, isosteric heats of adsorption ( Figure 3 ) follow a trend (Mg > Ni > Co > Fe > Mn > Zn >Cu) that unexpectedly does not correlate with the ionic radii. [ 68 ] A recent study by Yu [ 54 ] gives an explanation for the observed trend through a description of nuclear screening effects by M 2+ d-orbitals. Their fi rst-principles study reveals that the relative strength of the electrostatic interaction is dictated by the effective charge of the metal cation at the open coordination site where the CO 2 binds.…”

“…It also undergoes chemical substitution with a wide range of fi rst-row transition metals, which is perhaps only rivaled by MOFs of the type M-BTT (BTT 3− = 1,3,5-benzenetristetrazolate), where M = Mn, Fe, Co, Ni, Cu or Cd, [45][46][47][48] and M 3 (btc) 2 (btc 3− = 1,3,5-benzenetricarboxylate), where M = Cr, Cu, Zn, Mo, or Ru, [49][50][51][52][53] providing a mechanism for tuning the adsorption properties ( Figure 3 ) whilst retaining the same framework bonding motif. [ 54 ] Furthermore, all structural analogs within the M 2 (dobdc) family are of high crystalline quality, allowing for detailed studies of structure-property relationships and providing an experimental platform to test how accurately developing force fi elds can describe the guest interaction in slightly varying chemical environments. [ 55,56 ] Recent studies on this framework encompass a wide range of experimental and theoretical methodologies utilized to characterize interactions with various guests in the M 2 (dobdc) compound family ( Figure 3 ).…”