Metal Substitutions in the MOF-5 Metal-Organic Framework: A Hybrid Density Functional Theory Study

Doping properties of the MOF-5 metal-organic framework [Zn₄O(BDC)₃, BDC = benzodicarboxylate] are explored using density functional theory calculations, with hybrid functional. Our investigation primarily focused on the stability, electronic structure, and formation energy of MOF-5 when doped with an M atom (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Al), occupying a single Zn site per unit cell. Our findings reveal that MOF-5 exhibits insulating characteristics with an electronic band gap of 4.8 eV. However, after metal doping, impurity levels are observed throughout the band gap. Sc and Al introduce semioccupied levels close to the conduction band minimum, which can impart donor-like characteristics to the material. Formation energy calculations indicate that Sc, Al, Ti, and V exhibit stability in the single-positive charge state for Fermi energy values lower than 3 eV, while Cr, Mn, Fe, Co, and Ni are stable in neutral charge states. It is noteworthy that dopants with unpaired electrons retain this property when inserted at Zn sites, inducing local magnetization in MOF-5. Consequently, our findings suggest that the electronic properties of MOF-5 undergo drastic modification after the incorporation of specific metal dopants, indicating the potential for the development of metal-organic frameworks as functional materials.