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The reaction of HfCl4 with fumaric acid (C4H4O4, H2Fum) in a DMF/HCOOH solvent mixture at 120 °C for 24 h results in the formation of a defect‐free sample of Hf‐UiO‐66‐Fum with UiO‐66 structure type. Treatment of the (as)‐synthesized sample in boiling ethanol followed by a thermal treatment at 70 °C leads to a sample of composition [Hf6(μ3‐O)4(μ3‐OH)4(Fum)6]·18H2O·2EtOH. In the crystal structure the hexanuclear clusters {Hf6(μ3‐O)4(μ3‐OH)4} are twelve‐fold connected by C4H2O42– ions to form the framework with the fcu topology. This cluster connectivity was confirmed by a combination of characterization techniques methods, i.e. CHN analyses, N2 sorption as well as 1H‐NMR spectroscopic and thermogravimetric measurements. The MOF shows a thermal stability of T = 390 °C, a specific BET surface area of 389 m2·g–1 and a water uptake of 204 mg·g–1. The crystal structure was determined from powder X‐ray diffraction (PXRD) data, employing the Rietveld method. The compound crystallizes in the cubic space group Pn3 and is isostructural to Zr‐UiO‐66‐Fum. Only a small increase of the lattice parameter a from 17.8309(4) to 17.87978(14) Å is observed. [ABSTRACT FROM AUTHOR]

We report the discovery and characterization of two porous Ce(III)-based metal-organic frameworks (MOFs) with the V-shaped linker molecules 4,4'-sulfonyldibenzoate (SDB 2- ) and 4,4'-(hexafluoroisopropylidene)bis(benzoate) (hfipbb 2- ). The compounds of framework composition [Ce 2 (H 2 O)(SDB) 3 ] ( 1 ) and [Ce 2 (hfipbb) 3 ] ( 2 ) were obtained by using a synthetic approach in acetonitrile that we recently established. Structure determination of 1 was accomplished from 3D electron diffraction (3D ED) data, while 2 could be refined against powder X-ray diffraction (PXRD) data using the crystal structure of an isostructural La-MOF as the starting model. Their framework structures consist of chain-like inorganic building units (IBUs) or hybrid-BUs that are interconnected by the V-shaped linker molecules to form framework structures with channel-type pores. The composition of both compounds was confirmed by PXRD, elemental analysis, as well as NMR and IR spectroscopy. Interestingly, despite the use of (NH 4 ) 2 [Ce IV (NO 3 ) 6 ] in the synthesis, cerium ions in both MOFs occur exclusively in the + III oxidation state as determined by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). Thermal analyses reveal remarkably high thermal stabilities of ≥400 °C for the MOFs. Initial N 2 sorption measurements revealed the peculiar sorption behavior of 2 which prompted a deeper investigation by Ar and CO 2 sorption experiments. The combination with nonlocal density functional theory (NL-DFT) calculations adds to the understanding of the nature of the different pore diameters in 2 . An extensive quasi-simultaneous in situ XANES/XRD investigation was carried out to unveil the formation of Ce-MOFs during the solvothermal syntheses in acetonitrile. The crystallization of the two Ce(III)-MOFs presented herein as well as two previously reported Ce(IV)-MOFs, all obtained by a similar synthetic approach, were studied. While the XRD patterns show time-dependent MOF crystallization, the XANES data reveal the presence of Ce(III) intermediates and their subsequent conversion to the MOFs. The addition of acetic acid in combination with the V-shaped linker molecule was identified as the crucial factor for the formation of the crystalline Ce(III/IV)-MOFs.

The use of the V-shaped linker molecules 4,4'-oxydibenzoic acid (H 2 ODB) and 4,4'-carbonyldibenzoic acid (H 2 CDB) led to the discovery of two isoreticular Ce(IV)-based metal-organic frameworks (MOFs) of composition [CeO(H 2 O)(L)], L = ODB 2- , CDB 2- , denoted CAU-58 (CAU = Christian-Albrechts-University). The recently developed Ce-MOF synthesis approach in acetonitrile as the solvent proved effective in accessing Ce(IV)-MOF structures with infinite rod-shaped inorganic building units (IBUs) and circumventing the formation of the predominantly observed hexanuclear [Ce 6 O 8 ] cluster. For the structure determination of the isoreticular MOFs, three-dimensional electron diffraction (3D ED) and powder X-ray diffraction (PXRD) data were used in combination with density functional theory (DFT) calculations. [CeO(H 2 O)(CDB)] shows reversible H 2 O adsorption by stirring in water and thermal treatment at 190 °C, which leads to a unit cell volume change of 11%. The MOFs feature high thermal stabilities ( T > 290 °C), which exceed those of most Ce(IV)-MOFs and can be attributed to the infinite rod-shaped IBU. Surface and bulk oxidation states of the cerium ions were analyzed via X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge spectroscopy (XANES). While Ce(III) ions are observed by the highly surface-sensitive XPS method, the bulk material contains predominantly Ce(IV) ions according to XANES. Application of the MOFs as catalysts for the catalytic degradation of methyl orange in aqueous solutions was also studied. While degradation activity for both MOFs was observed, only CAU-58-ODB revealed enhanced photocatalytic activity under ultraviolet (UV) light. The photocatalytic mechanism likely involves a ligand-to-metal charge transfer (LMCT) from the linkers to the Ce(IV) centers. Analyses by XANES and inductively coupled plasma-optical emission spectroscopy (ICP-OES) demonstrate that leaching of Cerium ions as well as partial reduction of Ce(IV) to Ce(III) takes place during catalysis. At the same time, PXRD data confirm the structural stability of the remaining MOF catalysts.

Sonication-assisted liquid phase exfoliation was applied to six different layered coordination polymers (CPs) in aqueous surfactant solution. The resulting nanosheets were investigated for structural and compositional integrity and microscopic analysis gives insights into the relationship between the crystal structure of the materials and their exfoliability. Larger open pores seem to favour the production of nanosheets with higher aspect ratio of lateral size to thickness.

Herein is reported the utilization of acetonitrile as a new solvent for the synthesis of the three significantly different benchmark metal-organic frameworks (MOFs) CAU-10, Ce-UiO-66, and Al-MIL-53 of idealized composition [Al(OH)(ISO)], [Ce 6 O 4 (OH) 4 (BDC) 6 ], and [Al(OH)(BDC)], respectively (ISO 2- : isophthalate, BDC 2- : terephthalate). Its use allowed the synthesis of Ce-UiO-66 on a gram scale. While CAU-10 and Ce-UiO-66 exhibit properties similar to those reported elsewhere for these two materials, the obtained Al-MIL-53 shows no structural flexibility upon adsorption of hydrophilic or hydrophobic guest molecules such as water and xenon and is stabilized in its large-pore form over a broad temperature range (130-450 K). The stabilization of the large-pore form of Al-MIL-53 was attributed to a high percentage of noncoordinating -COOH groups as determined by solid-state NMR spectroscopy. The defective material shows an unusually high water uptake of 310 mg g -1 within the range of 0.45 to 0.65 p/p°. In spite of showing no breathing effect upon water adsorption it exhibits distinct mechanical properties. Thus, mercury intrusion porosimetry studies revealed that the solid can be reversibly forced to breathe by applying moderate pressures (≈60 MPa)., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)