Free energy of ligand removal in the metal-organic framework UiO-66

We report an investigation of the "missing-linker phenomenon" in the Zr-based metal organic framework UiO-66 using atomistic force field and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge-capping mechanism involves acetic acid or Cl-/H2O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the formation of molecular aggregates, which provide an additional driving force for ligand loss. These results are expected to be of relevance to a wide range of metal-organic frameworks

Supplementary Data for "How Strong is the Hydrogen Bond in Hybrid Perovskites?

DFT optimised structures for the hybrid perovskites with the X organic cation and the Y anion: POSCAR-X-Y-D3 NMRdata.zip with NMR data for the four Zn formate perovskites and the X organic cation: X.d

Supplementary information for "Anharmonic origin of large thermal displacements in the metal-organic framework UiO-67"

<p>Supplementary information for DOI: 10.1021/acs.jpcc.7b04757</p> <p>POSCAR-XXX: DFT optimised structures</p> <p>Phonons-XXX.zip: Folders containing the force constants (FORCE_SETS), the resulting phonon frequencies (mesh.yaml), phonon partial density of states (partial_dos.dat), animations of all phonon modes (anime.ascii) e.g. to be visualized in VMD and gifs of selected phonon modes.  </p> <p>XDATCAR-XXX: MD trajectories</p

Theoretical Optimization of Compositions of High-Entropy Oxides for the Oxygen Evolution Reaction**

High‐entropy oxides are oxides consisting of five or more metals incorporated in a single lattice, and the large composition space suggests that properties of interest can be readily optimised. For applications within catalysis, the different local atomic environments result in a distribution of binding energies for the catalytic intermediates. Using the oxygen evolution reaction on the rutile (110) surface as example, here we outline a strategy for the theoretical optimization of the composition. Density functional theory calculations performed for a limited number of sites are used to fit a model that predicts the reaction energies for all possible local atomic environments. Two reaction pathways are considered; the conventional pathway on the coordinatively unsaturated sites and an alternative pathway involving transfer of protons to a bridging oxygen. An explicit model of the surface is constructed to describe the interdependency of the two pathways and identify the composition that maximizes catalytic activity

Anharmonic Origin of Giant Thermal Displacements in the Metal–Organic Framework UiO-67

The crystallography of mechanically soft materials such as hybrid organic–inorganic compounds often reveals large thermal displacement factors and partially occupied lattice sites, which can arise from static or dynamic disorder. A combination of <i>ab initio</i> lattice dynamics and molecular dynamics simulations reveals the origin of the giant thermal displacements in the biphenyl-4,4′-dicarboxylate (BPDC) linker in the metal–organic framework UiO-67. The dihedral angle between the two phenyl rings has two equivalent minima at ±31°, which cannot be described by harmonic phonons. Instead, anharmonic switching between the minima results in the experimentally observed large thermal ellipsoids. The switching frequency is found to be similar in the topologically distinct framework IRMOF-10, suggesting that dynamic disorder is a general feature of MOFs based on BPDC and structurally similar linkers

Free Energy of Ligand Removal in the Metal–Organic Framework UiO-66

We report an investigation of the “missing-linker phenomenon” in the Zr-based metal–organic framework UiO-66 using atomistic force field and quantum chemical methods. For a vacant benzene dicarboxylate ligand, the lowest energy charge-capping mechanism involves acetic acid or Cl–/H2O. The calculated defect free energy of formation is remarkably low, consistent with the high defect concentrations reported experimentally. A dynamic structural instability is identified for certain higher defect concentrations. In addition to the changes in material properties upon defect formation, we assess the formation of molecular aggregates, which provide an additional driving force for ligand loss. These results are expected to be of relevance to a wide range of metal–organic frameworks