Synthesis of Fluoro-Bridged Ho3+ and Gd3+ 1,3,5-Tris(4-carboxyphenyl)benzene Metal-Organic Frameworks from Perfluoroalkyl Substances

Revealing Disorder, Sorption Locations and a Sorption-Induced Single Crystal-Single Crystal Transformation in a Rare-Earth fcu-Type Metal-Organic Framework

Rare-earth metal-organic frameworks (RE-MOFs) formed in the presence of fluoride donors are a group of complex and applicable MOFs. Determining structural complexity is crucial in applying such MOFs and has been achieved to uncover framework disorders in the important fcu framework topology MOF, Y-ndc-fcu-MOF (1). 1 is found to contain F- groups disordered over the μ3-face-capping sites in its secondary building unit (SBU) and framework distortions upon sorption of different guest molecules. The favored location of the guests is within the octahedral cage of 1 where they interact with the Y3+ centers. The size, shape, and interactions of the different guests lead to subtle distortions within the SBU and adoption of specific orientations of the naphthalene group of the 1,4-naphthalenedicarboxylate framework linkers. The sorption of DMF(l)/H2O(l) lowers the symmetry from cubic Fm3̅m (for MeOH(l), N2(g), CO2(g or l)) to cubic Pa3̅ (for DMF(l)/H2O(l)) symmetry with retention of the fcu topology, and conversion between the Pa3̅ and Fm3̅m structures is induced by solvent exchange. Such disorder and sorption locations and transformation are important considerations during the optimization and application of MOFs for sorption-based technologies.

Synthesis and Characterization of Highly Fluorinated Hydrophobic Rare-Earth Metal-Organic Frameworks (MOFs)

Tuning a material's hydrophobicity is desirable in several industrial applications, such as hydrocarbon storage, separation, selective CO2 capture, oil spill cleanup, and water purification. The introduction of fluorine into rare-earth (RE) metal-organic frameworks (MOFs) can make them hydrophobic. In this work, the linker bis(trifluoromethyl)terephthalic acid (TTA) was used to make highly fluorinated MOFs. The reaction of the TTA and RE3+ (RE: Y, Gd, or Eu) ions resulted in the primitive cubic structure (pcu) exhibiting RE dimer nodes (RE-TTA-pcu). The crystal structure of the RE-TTA-pcu was obtained. The use of the 2-fluorobenzoic acid in the synthesis resulted in fluorinated hexaclusters in the face-centered cubic (fcu) framework (RE-TTA-fcu), analogous to the UiO-66 MOF. The RE-TTA-fcu has fluorine on the linker as well as in the cluster. The MOFs were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis, and contact angle measurements.

Fluoro-bridged rare-earth metal-organic frameworks

Rare-earth (RE) metal-organic frameworks (MOFs) offer unique optical, electronic, and magnetic properties. RE metals tend to make binuclear metal nodes resulting in dense nonporous coordination networks. Three dimensional porous RE-MOFs have been reported by preparing bigger metal nodes based on metal clusters often found as hexaclusters or nonaclusters. The formation of metal clusters (>2 metal ions) generally requires the use of fluorinated organic molecules reported as modulators. However, it was recently discovered that these molecules are not modulators, rather they act as reactants and leave fluorine in the metal clusters. The formation and types of fluorinated RE metal clusters have been discussed. These fluorinated clusters offer higher connectivity which results in porous MOFs. The presence of fluorine in these metal clusters offers unique properties, such as higher thermal stability and improved fluorescence. This frontier summarizes recent progress and gives future perspective on the fluorinated metal clusters in the RE-MOFs.

Lanthanide Metal-Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties

Two fluoro-bridged lanthanide-containing metal-organic frameworks (MOFs) were synthesized using 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDC), a fluorinated modulator, and a lanthanide nitrate. The syntheses of MOFs containing Gd3+ or Tb3+ and a closely related MOF structure containing Ho3+, Gd3+, or Tb3+ are presented. The presence of the fluorinated metal chains in these MOFs is shown through single crystal X-ray diffraction, energy dispersion X-ray spectroscopy, 19F nuclear magnetic resonance, and X-ray photoelectron spectroscopy. Magnetic measurements reveal weak antiferromagnetic exchange between the Ln3+ ions mediated by fluoride anions along the zigzag ladder chains present in the crystal structures of these MOFs.