How Does the Fluorination of the Linker Affect the Stability of Trimesate-Based Coordination Polymers and Metal–Organic Frameworks?

UoC-7: A Bimetallic K-Zn-MOF with an Anionic Framework Based on Fluorinated Trimesate Ligands Exhibiting a Large CO2 Uptake

In solvothermal reactions of Zn(NO3)2×6H2O with K(H2mF-BTC) or K(H2dF-BTC) in DMF/ethanol or DMA/ethanol solvent mixtures, single crystals of the MOFs UoC-7(1F) and UoC-7(2F) were obtained crystallizing in the hexagonal space group P63/m (no. 176) (H3BTC: 1,3,5-benzenetricarboxylic acid; mF-/dF: mono-/difluoro; DMF: N,N-dimethylformamide; DMA: N,N-dimethylacetamide; UoC: University of Cologne). According to the general composition [(CH3)2NH2][K2Zn3(mF-/dF-BTC)3(H2O)]×solvent, UoC-7 consists of an anionic bimetallic framework. The charge is compensated by a (CH3)2NH2 + cation stemming from the (partial) hydrolysis of the solvent. The crystal structure shows large channels along the hexagonal [001] direction, which accommodate the cations as well as solvent molecules. Surface areas (SBET) of 2740 m2/g (UoC-7(1F)) and 1643 m2/g (UoC-7(2F)) were obtained from N2 sorption measurements. UoC-7 shows structural similarities to the MOF NKU-521 with a 5-(1H-tetrazol-5-yl)isophthalate linker. Both MOFs exhibit a 4,7,8T14 topology. Despite smaller channels in UoC-7 compared to NKU-521, the CO2 uptake is considerably higher (~164 cm3/g at 1 bar/293 K) being one of the highest CO2 uptakes observed up to now.

Perfluoroalkyl-Decorated Noble-Metal-Free MOFs for the Highly Efficient One-Pot Four-Component Coupling between Aldehydes, Amines, Alkynes, and Flue Gas CO2

The non-noble-metal catalysed-multicomponent reactions between flue gas CO2 and cheap industrial raw stocks into high value-added fine chemicals is a promising manner for the ideal CO2 utilization route. To achieve this, the key fundamental challenge is the rational development of highly efficient and facile reaction pathway while establishing compatible catalytic system. Herein, through the stepwise solvent-assisted linker installation, post-synthetic fluorination and metalation, we report the construction of a series of perfluoroalkyl-decorated noble-metal-free metal-organic frameworks (MOFs) PCN-(BPY-CuI)-(TPDC-Fx ) [BPY=2,2'-bipyridine-5,5'-dicarboxylate, TPDC-NH2 =2'-amino-[1,1':4',1''-terphenyl]-4,4''-dicarboxylic acid] that can catalyze the one-pot four-component reaction between alkyne, aldehyde, amine and flue gas CO2 for the preparation of 2-oxazolidinones. Such assembly endows the MOFs with superhydrophobic microenvironment, superior water resistance and highly stable catalytic site, leading to 21 times higher turnover numbers than that of homogeneous counterparts. Mechanism investigation implied that the substrates can be efficiently enriched by the MOF wall and then the adsorbed amine species act as an extrinsic binding site towards dilute CO2 through their strong preferential formation to carbamate acid. Moreover, density functional theory calculations suggest the tetrahedral geometry of Cu in MOF offers special resistance towards amine poisoning, thus maintaining its high efficiency during the catalytic process.

KC9H5O6(H2O): A Promising UV Nonlinear-Optical Material with Large Birefringence Based on a π-Conjugated (C9H5O6)- Group

In order to meet the growing needs for the laser technology and optics industries, the goal is to find suitable fundamental building blocks with large nonlinear-optical (NLO) coefficients and birefringence for an excellent-performance NLO or birefringent system. Via preliminary investigations and calculations, it has been found that the planar π-conjugated group (C₉H₅O₆)^- possesses large polarizability anisotropy (δ) and hyperpolarizability (β_max), comparable to well-known groups such as (B₃O₆)^3-, (C₃N₃O₃)^3-, etc. Herein, we report a new alkali-metal 3,5-dicarboxybenzoate, KC₉H₅O₆(H₂O) (KH₂BTC), which crystallized in the acentric space group Pna2₁. Second-harmonic-generation (SHG) measurements of KH₂BTC under 1064 nm laser radiation show that the SHG response of KH₂BTC is 1.2 times that of KDP with type I phase-matching behavior. Birefringence measurements show that KH₂BTC owns a large birefringence of about 0.372 at 550 nm. The band gap of KH₂BTC obtained by ultraviolet (UV) diffuse-reflectance spectroscopy is 3.91 eV, indicating that KH₂BTC has potential applications as UV NLO or birefringent materials. Theoretical calculation further confirmed that the impressive optical properties of KH₂BTC are derived from the large polarizability anisotropy of the (C₉H₅O₆)^- anions.

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

Synthesis, supramolecular isomerism, and photoluminescence of scandium(III) complexes with tetrafluoroterephthalate ligand

Here we present a new family of seven Sc(III) complexes with tetrafluoroterephthalate ligand (tFBDC2−), having non-polymeric and polymeric 2D and 3D structures. These complexes are characterized by SC XRD, PXRD,...

UoC-6: a first MOF based on a perfluorinated trimesate ligand

Reaction of Sc(NO3)3·5H2O with K(H2 pF-BTC) – the monopotassium salt of perfluorinated trimesic acid – led to the formation of single crystals of [ Sc ( p F − BTC ) ( H 2 O ) 3 ] ∞ 1 ⋅ 4 H 2 O ${}_{\infty }{}^{1}\left[\text{Sc}\left(pF-\text{BTC}\right){\left({\text{H}}_{2}\text{O}\right)}_{3}\right]\cdot 4{\text{H}}_{2}\text{O}$ ( P 1 ‾ $P‾{1}$ , Z = 2). DTA/TGA measurements revealed that all water molecules were released below 200 °C. Using powder synchrotron radiation diffraction data, the crystal structure of the residue of the dehydration was elucidated and the results confirmed the formula [ Sc ( p F − BTC ) ] ∞ 3 ${}_{\infty }{}^{3}\left[\text{Sc}\left(pF-\text{BTC}\right)\right]$ (Fddd, Z = 16). The compound is similar, but not isostructural to the recently published UoC-4 (I41/amd, Z = 8; UoC: University of Cologne) with a difluorinated trimesate (dF-BTC3–) as connecting linker. Both compounds can be classified as metal-organic frameworks (MOFs) consisting of a 3D network of Sc3+ nodes connected by the fluorinated trimesate ligands. They contain small pores, but their opening windows are too small for any guest molecules to pass. Remarkably, UoC-4 with a lower symmetric ligand (dF-BTC3–) crystallizes in a higher symmetry space group (I41/amd) than UoC-6 (Fddd). This can be rationalized by increasing torsion angles of the carboxylate moieties in the pF-BTC3– ligand.

Octafluorobiphenyl-4,4′-dicarboxylate as a ligand for metal-organic frameworks: progress and perspectives

While metal-organic frameworks based on aromatic carboxylates are very numerous and well investigated, the chemistry of their fully fluorinated analogues is at the very beginning. This minireview aims at summarizing all metal complexes with octafluorobiphenyl-4,4′-dicarboxylate (oFBPDC2−) anion and in particular, porous coordination polymers, their syntheses, crystal structures and functional properties highlighting the importance of further investigation of such systems.

Stable metal-organic frameworks with low water affinity built from methyl-siloxane linkers

A tetracarboxylic acid with a methyl-substituted siloxane core (L-H₄) has been prepared and applied in the construction of water stable MOFs with low water affinity. L-H₄ itself crystallizes as an interpenetrated 3D hydrogen-bonded network. Reaction of L-H₄ with Zr^IV/Hf^IV gave IMP-32-Zr/Hf - both 3D MOFs of scu topology.