Halogenated MOF-5 variants show new configuration, tunable band gaps and enhanced optical response in the visible and near infrared

Abstract

Inspired by recent experimental fabrication of mono-halogenated versions of Metal-Organic Framework MOF-5 (i.e., X-MOF-5, X = F to I) and some experimentally known fully halogenated MOF compounds, we systematically studied frameworks incorporating full halogenation of the BDC linkers of the prototypical Iso-Reticular Metal-Organic Framework (IRMOF) series, exemplified by MOF-5. Using quantum chemistry calculations, we find that halogenation leads to a 90° rotation of the aryl group, which is mainly ascribed to overcrowding between halogen atoms and the carboxyl and benzene ring and strong repulsion among in-plane atoms/groups. The 90° configuration decreases the repulsion, and maximizes the stabilization energy, and is therefore more stable than 0° configuration. We find that the band gap can be tuned from 4.1 to 1.5 eV as we go from F, Cl, Br, to I. This extends the optical response of these experimentally accessible materials through the visible and infrared region. We have also considered a broader range of new materials that substitute various metals for Zn. Totally, 70 materials were systematically examined computationally including (MO)(BDC-Z) (M = Zn, Cd, Be, Mg, Ca, Sr, Ba; Z = H, F, Cl, Br, I). For the full range of materials, we calculate band gaps of 4.2 to 1.0 eV, corresponding to a threshold of absorption of 290-1240 nm. Four selected materials were tested for stability using short 5 ps molecular dynamics simulations up to 600 K. The new materials with the smallest band gaps could potentially be used in near-infrared (NIR) light-emitting devices. Other properties, e.g., bulk moduli, formation energy, chemical bonding, and optical properties, were also investigated. The present results may provide new materials for use as novel photocatalysts, photoactive materials for photovoltaic cells, or functional devices in nanoelectronics and optoelectronics.

Two New Coordination Polymers with UO22+ Units and Fluorinated Aromatic Carboxylate Linkers

“…These torsion angles are surprising, as the occupancy of F2 was refined to a higher value (65 %) than that of F3 (35 %). Nevertheless, a higher torsion angle is observed with F3 in α position, which is different to most reports in the literature , . In our former work with the monofluorinated 4‐ mF ‐BPTC 4– linker we found a torsion angle of 28.9(9)°, which is significantly larger than those found for anion A in this work.…”

“…Several years ago we started to synthesize fluorinated aromatic carboxylic acids,, which – in a next step – were used to synthesize new CPs and MOFs with these linkers . With respect to their structural chemistry it is a remarkable feature that the torsion angle between the phenyl ring and the carboxylate group is no longer close to 0° as found in most MOFs and CPs with non‐fluorinated ligands, but significantly increased especially for fluoro substituents in α position and even more for perfluorinated ligands , . In this respect, it seems to be worthwhile to examine how the structural chemistry of uranium‐based CPs and MOFs develops, when fluorinated aromatic carboxylate ligands are introduced.…”

Metal–Organic‐Framework‐Based Catalysts for Photoreduction of CO2

“…Furthermore, the functionalizations of organic linkers [94,95,97,98] and the modifications of the structures of metal clusters [99,100] in MOFs can both reduce their HOMO-LUMO gap width, leading to their expanded light-absorption capacity. Hence, most MOF photocatalysts can exhibit photocatalytic activities in a visible range, which is favorable to the improved light-utilization efficiency.…”

“…[66][67][68]94,95,98,99,151] Amino-modified, photosensitizer-functionalized, and electron-rich conjugated linkers possess broad optical absorptions, excess electron densities, and strong interactions with CO 2 , which could be selected to act as linkers in MOF photocatalysts with high catalytic activities.…”

“…Moreover, the functionalization of organic linkers in synthesized MOFs (e.g., the inlay of foreign metal cations into the organic linkers, and the PSE and PSM of organic linkers) is an effective strategy for the formation of new MOF materials with broadened optical absorptions and enhanced CO 2 adsorption capacities. [66][67][68]94,95,98,99,151]…”