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Ruthenium MOF [Ru3(BTC)2Yy] ⋅ Gg (BTC=benzene‐1,3,5‐tricarboxylate; Y=counter ions=Cl−, OH−, OAc−; G=guest molecules=HOAc, H2O) is modified via a mixed‐linker approach, using mixtures of BTC and pyridine‐3,5‐dicarboxylate (PYDC) linkers, triggering structural defects at the distinct Ru2 paddlewheel (PW) nodes. This defect‐engineering leads to enhanced catalytic properties due to the formation of partially reduced Ru2‐nodes. Application of a hydrogen pre‐treatment protocol to the Ru−MOFs, leads to a further boost in catalytic activity. We study the benefits of (1) defect engineering and (2) hydrogen pre‐treatment on the catalytic activity of Ru−MOFs in the Meerwein‐Ponndorf‐Verley reaction and the isomerization of allylic alcohols to saturated ketones. Simple solvent washing could not avoid catalyst deactivation during recycling for the latter reaction, while hydrogen treatment prior to each catalytic run proved to facilitate materials recyclability with constant activity over five runs. [ABSTRACT FROM AUTHOR]

Abstract: Three Zr‐oxo‐cluster node and porphyrin‐linker based MOFs, MOF‐525, PCN‐222 and PCN‐224 exhibiting different linker connectivities of 12, 8 and 6 and their porphyrin‐linker metalated analogues, were synthesized and tested as catalysts for CO2 fixation by using the cycloaddition of CO2 and propylene oxide to propylene carbonate as the test reaction. In general, the catalytic activity correlates with the connectivity of the Zr‐oxo nodes. The lowest connected PCN‐224 (6‐fold) exhibits a superior catalytic activity in this series, while higher connected PCN‐222 (8‐fold) and MOF‐525 (12‐fold) are less active. Interestingly, the catalytic activity of the higher connected MOFs significantly depends on defects. The (ideally) 12‐connected MOF‐525, however exhibiting 16% of missing linker defects, features a higher catalytic activity compared to the 8‐connected PCN‐222 with less defects. The overall catalytic activity is increased in dual site catalysts when the porphyrin linkers are metalated with Mn(III) and Zn(II) centers, which are acting as additional Lewis acid sites. Here, the metalated MOFs with higher connectivity exhibit the highest activity. [ABSTRACT FROM AUTHOR]

Tailoring defects in metal–organic frameworks is important for enhancing sorption and reaction properties. Defects in UiO-66 have been characterized for the first time by using water adsorption measurements. We found that the defect-induced hydrophilicity, quantitatively expressed by the Henry constant and the saturation water uptake, correlates well with the catalytic performance in the cyanosilylation of benzaldehyde. [ABSTRACT FROM AUTHOR]

By employing various synthetic conditions, such as Cu(NO3)2·3H2O and Cu(BF4)2·6H2O as copper ion sources and different solvents, defect-engineered analogues of metal–organic framework (MOF) [Cu3(BTC)2] (HKUST-1; BTC = 1,3,5-benzenetricarboxylate) with isophthalate (IP) incorporation (DEMOFs) were synthesised and characterised by powder XRD, SEM, IR spectroscopy, thermogravimetric analysis, NMR spectroscopy and N2 sorption. The results show that the choice of counter ions impacts the properties of the samples especially at high concentrations of IP. The combination of DMF and Cu(BF4)2·6H2O turns out to be superior for DEMOFs with IP incorporation up to 25 %. Ultrahigh-vacuum IR spectra recorded upon CO adsorption together with the results of X-ray photoelectron spectroscopic studies show the generation of coordinatively unsaturated Cu+ sites. The results suggest the presence of two different defect types, that is, missing-linker defects and missing paddlewheels for high concentrations of IP. [ABSTRACT FROM AUTHOR]

By employing the mixed-component, solid-solution approach, various functionalized ditopic isophthalate (ip) defect-generating linkers denoted 5-X-ipH2, where X=OH ( 1), H ( 2), NH2 ( 3), Br ( 4), were introduced into the mixed-valent ruthenium analogue of [Cu3(btc)2] n (HKUST-1, btc=benzene-1,3,5-tricarboxylate) to yield Ru-DEMOFs (defect-engineered metal-organic frameworks) of the general empirical formula [Ru3(btc)2− x(5-X-ip) xY y] n. Framework incorporation of 5-X-ip was confirmed by powder XRD, FTIR spectroscopy, ultrahigh-vacuum IR spectroscopy, thermogravimetric analysis, 1H NMR spectroscopy, N2 sorption, and X-ray absorption near edge structure. Interestingly, Ru-DEMOF 1 c with 32 % framework incorporation of 5-OH-ip shows the highest BET surface area (≈1300 m2 g−1, N2 adsorption, 77 K) among all materials (including the parent framework [Ru3(btc)2Y y] n). The characterization data are consistent with two kinds of structural defects induced by framework incorporation of 5-X-ip: modified paddlewheel nodes featuring reduced ruthenium sites (Ru δ+, 0< δ<2, type A) and missing nodes leading to enhanced porosity (type B). Their relative abundances depend on the choice of the functional group X in the defect linkers. Defects A and B also appeared to play a key role in sorption of small molecules (i.e., CO2, CO, H2) and the catalytic properties of the materials (i.e., ethylene dimerization and the Paal-Knorr reaction). [ABSTRACT FROM AUTHOR]

Host-guest inclusion properties of UiO-66 and UiO-67 metal-organic frameworks have been studied using ferrocene (FeCp2) as probe molecule. According to variable-temperature solid-state 1H and 13C CP-MAS-NMR, two different environments exist for adsorbed FeCp2 inside UiO-66 and UiO-67, which have been assigned to octahedral and tetrahedral cavities. At room temperature, a rapid exchange between these two adsorption sites occurs in UiO-67, while at -80 °C the intracrystalline traffic of FeCp2 through the triangular windows is largely hindered. In UiO-66, FeCp2 diffusion is already impeded at room temperature, in agreement with the smaller pore windows. Palladium nanoparticles (Pd NPs) encapsulated inside UiO-66 and UiO-67 have been prepared by chemical vapor infiltration of (allyl)Pd(Cp) followed by UV light irradiation. Infiltration must be carried out at low temperature (-10 °C) to avoid uncontrolled decomposition of the organometallic precursor and formation of Pd NPs at the external surface of the MOF. The resulting Pd-MOFs are shape selective catalysts, as shown for the hydrogenation of carbonyl compounds with different steric hindrance. [ABSTRACT FROM AUTHOR]

A controlled secondary building unit approach (CSA) was employed to obtain a series of ruthenium metal-organic frameworks (MOFs) of the general formula [Ru3(BTC)2X x] ·G g (BTC = 1,3,5-benzenetricarboxylate; X = counter-anion, G = guest molecules) which are structural analogues of [M3(BTC)2] (M = Cu, Zn, Ni, Cr, Mo). The compounds [Ru2(OOCR)4X] and [Ru2(OOCCH3)4]Y were varied as Ru sources for CSA; namely strong coordinating X (Cl-) and weakly coordinating Y ([BF4]- or [BPh4]-) as well as the alkyl groups at the carboxylate ligand [R = CH3 or C(CH3)3] were utilized. Four phase-pure Ru-MOFs were obtained: [Ru3(BTC)2Cl0.5(OH)] ·(AcOH)1.5 ( 1), [Ru3(BTC)2Cl1.2(OH)0.3] ·(H3BTC)0.15(AcOH)2.4(PivOH)0.45 ( 2), [Ru3(BTC)2F0.5(OH)] ·(AcOH)1.0 ( 3) and [Ru3(BTC)2(OH)1.5] ·(H3BTC)0.5 ·(AcOH)1.4 ( 4) {AcOH = CH3COOH, PivOH = (CH3)3CCOOH}. The series of characterization data support the analytical composition and isostructural nature of 1- 4, i.e. powder X-ray diffraction (PXRD), IR- and 1H-NMR spectroscopy, thermal gravimetric analysis (TGA) and N2 sorption were employed. The valence state of the Ru-sites were studied by X-ray absorption spectroscopy (XAS). The chosen precursors for CSA and optimized synthesis, work-up and activation protocols allowed improvement of the overall crystallinity, purity (i.e., residual solvent molecules) and surface area of the Ru-MOF materials. [ABSTRACT FROM AUTHOR]

When the dinuclear Ru II,II precursor [Ru 2 (OOCCH 3 ) 4 ] is employed under redox-inert conditions, a Ru II,II analogue of HKUST-1 was successfully prepared and characterized as a phase-pure microcrystalline powder. X-ray absorption near-edge spectroscopy confirms the oxidation state of the Ru centers of the paddle-wheel nodes in the framework. The porosity of 1371 m 2 /mmol of Ru II,II -HKUST-1 exceeds that of the parent compound HKUST1 (1049 m 2 / mmol).