Quasi-1D physics in metal-organic frameworks: MIL-47(V) from first principles

Abstract

SummaryThe geometric and electronic structure of the MIL-47(V) metal-organic framework (MOF) is investigated by using ab initio density functional theory (DFT) calculations. Special focus is placed on the relation between the spin configuration and the properties of the MOF. The ground state is found to be antiferromagnetic, with an equilibrium volume of 1554.70 Å3. The transition pressure of the pressure-induced large-pore-to-narrow-pore phase transition is calculated to be 82 MPa and 124 MPa for systems with ferromagnetic and antiferromagnetic chains, respectively. For a mixed system, the transition pressure is found to be a weighted average of the ferromagnetic and antiferromagnetic transition pressures. Mapping DFT energies onto a simple-spin Hamiltonian shows both the intra- and inter-chain coupling to be antiferromagnetic, with the latter coupling constant being two orders of magnitude smaller than the former, suggesting the MIL-47(V) to present quasi-1D behavior. The electronic structure of the different spin configurations is investigated and it shows that the band gap position varies strongly with the spin configuration. The valence and conduction bands show a clear V d-character. In addition, these bands are flat in directions orthogonal to VO6 chains, while showing dispersion along the the direction of the VO6 chains, similar as for other quasi-1D materials.

Mechanical Properties from Periodic Plane Wave Quantum Mechanical Codes: The Challenge of the Flexible Nanoporous MIL-47(V) Framework

“…For the EOS structure with a 2 × 2 × 6 kgrid, the Pulay stress amounts to −0.125 GPa. This value is of the same order of magnitude as calculated transition pressures between the large-and narrow-pore phase from literature (82-125 MPa), 23 which indeed supports the proposed mechanism shown in Fig. 4.…”

“…MIL-53(Al)), it only shows breathing behavior under the application of a significant external pressure. 23,26 Using the insights and methodology developed in the previous sections, the narrow-pore (NP) version of the MIL-47(V) will now be investigated (Fig. 1b).…”

“…In addition, the combination of metal(-oxide) nodes and organic linkers may lead to the emergence of low dimensional physics. 16,20,21,23,29 Furthermore, both covalent and noncovalent interactions are essential to reproduce the equilibrium structure and thus also the unit cell. These interactions and the interplay between them are of fundamental importance to explain the breathing phenomena of some MOFs.…”

“…25,40,41 In contrast, MIL-47(V) shows breathing under significant mechanical pressure. 23,26 Because of this more rigid nature than other breathing MOFs, MIL-47(V) is assumed to be better-behaved in the computations, and thus more suitable for investigating methodological aspects.…”

A Flexible Photoactive Titanium Metal–Organic Framework Based on a [TiIV3(μ3‐O)(O)2(COO)6] Cluster

“…Thec onduction band is made up of Ti states (cyan curves), as also seen in other MOFs. [52] TheHatoms present on the Ti clusters only show contributions deep inside the valence bands (pink curves) and do not modify the electronic structure around the band gap.…”