Computational chemistry
Defect hydroxides in UiO-66 shuttle protons
Open access · cc by · source: Europe PMC
Simulations of missing-linker UiO-66 put charge-balancing OH on under-coordinated Zr and show those sites swap between hydroxide and water by rapid proton transfer with extra-framework water.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
AIMD of defective UiO-66 makes a proton shuttle that diffraction cannot see. Average Zr⋯O = 2.23 Å matches 300 K experiment, but a direct O0–O1 proton-transfer barrier is only 6.5 kJ mol⁻¹ versus 27.5 kJ mol⁻¹ for an O3-mediated path. NH₃ binds 110.1 versus 75.8 kJ mol⁻¹ at defect versus perfect regions; water can leave, exposing frustrated-Lewis-pair-like Zr. The dynamics are computed, not a measured catalytic turnover.
Evidence for the claim as stated.
MD that is later tested in a cuvette is not the same deliverable as MD that stays inside the computer. Mpro peptides have micromolar IC₅₀ values; GFP AIMD proton-transfer times disagree with 3/10 ps FSRS phases; UiO-66 proton hops are invisible to time-averaged XRD. A student who says 'MD showed the mechanism' must say whether a wet observable confirmed it.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
MD that is later tested in a cuvette is not the same deliverable as MD that stays inside the computer. Mpro peptides have micromolar IC₅₀ values; GFP AIMD proton-transfer times disagree with 3/10 ps FSRS phases; UiO-66 proton hops are invisible to time-averaged XRD. A student who says 'MD showed the mechanism' must say whether a wet observable confirmed it.
Study at a glance
- Design
- Computational / modelling — PBE0+D3 and AIMD of defective UiO-66 proton transfer and NH3 binding
- N
- Periodic DFT/AIMD study of MOF defects — no sample N
- Population
- Defective UiO-66 zirconium MOF models
- Outcome
- Dynamic Brønsted acidity and proton-transfer barriers at defect sites
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
Defect hydroxides in UiO-66 shuttle protons
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Mean AIMD Zr⋯O distance was 2.23 Å, matching 2.24(3) Å experiment at 300 K.
Averaging the two Zr⋯O distances over the trajectory of the whole AIMD simulation, we obtain a mean Zr⋯O distance of 2.23 Å, which is in excellent agreement with the experimental Zr⋯O distance of 2.24(3) Å at the same temperature of 300 K by Trickett et al. and 2.22 Å by Øien et al. at 100 K.
Direct proton transfer barrier is 6.5 kJ mol−1, 21.0 kJ mol−1 below the O3-mediated path.
We estimate the transition barrier of this single proton transfer process in the same manner as the O3 mediated case, which is found to be only 6.5 kJ mol −1 per defect centre (at the PBE0 + D3 level of theory), 21.0 kJ mol −1 per defect centre lower than the two-step O3 mediated case.
Key findings
Average Zr⋯O = 2.23 Å matches 300 K experiment. Direct O0–O1 proton transfer barrier is only 6.5 kJ mol−1 versus 27.5 for an O3-mediated path. NH3 binds 110.1 vs 75.8 kJ mol−1 at defect vs perfect regions. Water can leave, exposing frustrated Lewis pair-like Zr sites.
Methodology
Authors ran PBE0+D3 static optimisations and AIMD at 100–700 K on defective UiO-66, compared Zr–O distances to diffraction, estimated proton-transfer barriers, and used NH3 binding as a Brønsted-acidity probe.
Limitations
The dynamics are computed; they are invisible to time-averaged XRD and are not a measured catalytic turnover of a substrate.
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