Understanding and solving disorder in the substitution pattern of amino functionalized MIL-47(V)

Abstract

Electronic energies and elastic constants of four amino functionalized MIL-47(V) supercells were computed using plane wave density functional theory to determine the influence of the substituent positions on the organic linker. An inverse relationship between the ab initio energies and the elastic constants was found, indicating that the high electronic stability correlates with high mechanical stability. Torsion in all supercells was induced upon substitution, which caused strain in the NH₂-MIL-47(V) supercell. The combined effect of the substituent bulkiness and the induced torsion reduced the pore volume of the NH₂-MIL-47(V) structures by >7% and the surface area by >14% with respect to MIL-47(V). This reduction was confirmed by lower saturation capacities of methane, CO₂ and benzene. When unfavourable substituent positions are chosen, large torsions caused a further reduction of the saturation capacity. Differences in surface area, pore volume and saturation capacity illustrate the importance of choosing the correct NH₂-MIL-47(V) supercell.