Monitoring Mechanical, Electronic, and Catalytic Trends in a Titanium Metal Organic Framework Under the Influence of Guest-Molecule Encapsulation Using Density Functional Theory

Abstract

In this study, we conduct a density functional theory investigation to study the mechanical stability of a titanium-based metal organic framework (MOF-901), which was hypothetically assumed to possess 2D characteristics. It is systematically found that the encapsulation of methanol enhances the mechanical stability of MOF-901 as the elastic tensors Cij of MOF-901∙nMeOH are higher than the corresponding Cij quantities reported for solvent-free MOF-901. Moreover, the 2D characteristics of MOF-901 is confirmed by verifying the negative values of C33. At the same time, the band gap of MOF-901 is observed to be solvent-dependent. In its pure form, MOF-901 possesses a direct gap (Eg) of 2.07 eV, with the valence and conduction bands mainly constituted by electrons of 4-aminobenzoate linkers. Introducing methanol into MOF-901 causes distortion to the 4-aminobenzoate geometry, thereby induces electronic degeneracy to the conduction bands. Consequently, Eg is narrowed to 1.84 eV with 5.7 wt% MeOH or 1.63 eV with 11.4 wt% MeOH. Hence, it is possible to tailor the band gap of MOF-901 by controlling methanol guest, which only acquires van der Waals interaction to the framework. In addition, our theoretical prediction shows a Ti(IV) site can undergo electronic hopping to become Ti(III) under the effect of visible light (~440–443 nm). Then, Ti(III) is capable of breaking the C-Br bond in ethyl α-bromophenylacetate spontaneously, which in turn activates the polymerization of methyl methacrylate with an energy barrier of 0.30 eV.

Electronic Structure Modeling of Metal–Organic Frameworks

“…A similar conclusion was reached in another study examining a larger selection of MOFs with an analogous metal and ligand chemistry, Figure . The data in Figures and also highlight a common theme in the literature: GGA functionals tend to underestimate both the experimental and hybrid-computed band gap, and the addition of exact (HF) exchange is necessary to recover more realistic electronic band gaps. − In sum, assuming a sufficiently high-fidelity basis set, pure GGA functionals are the lowest level of theory required to provide a reasonable electronic description of most MOFs. However, the recovery of experimental semiconducting properties requires the incorporation of some exact exchange.…”

Metal–Organic Frameworks: Molecules or Semiconductors in Photocatalysis?

“…At the very least, we can expect the solvent to affect and even shape the electric field within the pore. This affects not only the electrochemical properties described in Section 4.2, but also the band energies [110–112] . We know these effects to be very real, through, for example, the dependency of C=O vibrational modes [113] …”

Synthesis and Characterization of MOF‐Derived Structures: Recent Advances and Future Perspectives

“…MOFs contain metal oxo-clusters and organic linkers, resulting in electronic transitions between the valence band and conductive band of metal oxo-clusters or between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of organic linkers when exposed to light with the appropriate energy. [346] This leads to the formation of an absorption spectrum with multiple bands, depending on the constituents promoting electron transitions. Additionally, UV-vis DRS is valuable for studying electronic properties, ligand interactions, and photochemical reactions in MOF derivatives.…”