Detailed Structure Analysis of Atomic Positions and Defects in Zirconium Metal–Organic Frameworks

We report the structure of the Zr metal–organic frameworks (MOFs) UiO-66 and UiO-67 to very fine detail using synchrotron single-crystal X-ray diffraction and the synthesis method used to obtain single crystals. Zr terephthalate MOF UiO-66 is known to have missing linkers, and the nature of these are shown to be coordinating water and solvent molecules. Single crystals of the isoreticular material UiO-67 does not show such missing linker defects

Detailed Structure Analysis of Atomic Positions and Defects in Zirconium Metal–Organic Frameworks

We report the structure of the Zr metal–organic frameworks (MOFs) UiO-66 and UiO-67 to very fine detail using synchrotron single-crystal X-ray diffraction and the synthesis method used to obtain single crystals. Zr terephthalate MOF UiO-66 is known to have missing linkers, and the nature of these are shown to be coordinating water and solvent molecules. Single crystals of the isoreticular material UiO-67 does not show such missing linker defects

A Gold Exchange: A Mechanistic Study of a Reversible, Formal Ethylene Insertion into a Gold(III)–Oxygen Bond

The Au­(III) complex Au­(OAc^F)₂(tpy) (<b>1</b>, OAc^F = OCOCF₃; tpy = 2-<i>p</i>-tolylpyridine) undergoes reversible dissociation of the OAc^F ligand <i>trans</i> to C, as seen by ¹⁹F NMR. In dichloromethane or trifluoroacetic acid (TFA), the reaction between <b>1</b> and ethylene produces Au­(OAc^F)­(CH₂CH₂OAc^F)­(tpy) (<b>2</b>). The reaction is a formal insertion of the olefin into the Au–O bond <i>trans</i> to N. In TFA this reaction occurs in less than 5 min at ambient temperature, while 1 day is required in dichloromethane. In trifluoroethanol (TFE), Au­(OAc^F)­(CH₂CH₂OCH₂CF₃)­(tpy) (<b>3</b>) is formed as the major product. Both <b>2</b> and <b>3</b> have been characterized by X-ray crystallography. In TFA/TFE mixtures, <b>2</b> and <b>3</b> are in equilibrium with a slight thermodynamic preference for <b>2</b> over <b>3</b>. Exposure of <b>2</b> to ethylene-<i>d</i>₄ in TFA caused exchange of ethylene-<i>d</i>₄ for ethylene at room temperature. The reaction of <b>1</b> with <i>cis</i>-1,2-dideuterioethylene furnished Au­(OAc^F)­(<i>threo</i>-CHDCHDOAc^F)­(tpy), consistent with an overall <i>anti</i> addition to ethylene. DFT­(PBE0-D3) calculations indicate that the first step of the formal insertion is an associative substitution of the OAc^F <i>trans</i> to N by ethylene. Addition of free ^–OAc^F to coordinated ethylene furnishes <b>2</b>. While substitution of OAc^F by ethylene <i>trans</i> to C has a lower barrier, the kinetic and thermodynamic preference of <b>2</b> over the isomer with CH₂CH₂OAc^F <i>trans</i> to C accounts for the selective formation of <b>2</b>. The DFT calculations suggest that the higher reaction rates observed in TFA and TFE compared with CH₂Cl₂ arise from stabilization of the ^–OAc^F anion lost during the first reaction step

Probing Reactive Platinum Sites in UiO-67 Zirconium Metal–Organic Frameworks

We present three methods of the synthesis of zirconium metal–organic framework UiO-67 functionalized with platinum bipyridine coordination complexes (bpydcPt^IICl₂ and bpydcPt^IVCl₄) acting as linkers in the MOF framework. These Pt complexes can be reduced to bpydcPt⁰ under flow of H₂ gas in the 600–700 K range, as probed by a sophisticated parametric refinement of in situ EXAFS data. IR spectroscopy testifies the high coordinative unsaturation of the reduced centers, able to form bpydcPt⁰(CO)₂ dicarbonyl complexes upon CO adsorption. The large pore size of UiO-67 allows for ligand exchange between 2 Cl^– and even bulky ligands such as toluene-3,4-dithiol. Framework bpydcPt^IICl₂ complexes can also be oxidized at room temperature to bpydcPt^IVBr₄ through oxidative addition of liquid Br₂. XANES spectroscopy was used to monitor the changes in the Pt oxidation state along the observed reactions. Platinum bipyridine-functionalized UiO-67-Pt displays the same exceptional stability as the parent material as testified on both long and local range by in situ XRPD and Pt L₃-edge EXAFS data