Breath analysis reveals a wealth of information through the presence of hundreds of volatile organic compounds (VOCs) produced by metabolic processes. Particular combinations of VOCs can serve as chemical signatures for disease diagnosis. However, the inherent humidity in exhaled breath poses significant challenges for effective VOC capture using adsorbent materials. In this study, we present a groundbreaking approach that combines advanced modeling methods with experimental validation to enhance VOC recovery via post-synthetic modification of a well-studied metal-organic framework, MOF-808. Through the incorporation of fluorinated functional groups, we effectively modified the pore environment to exhibit hydrophobic properties, thereby enhancing its capacity for the selective capture of VOCs. The best performing derivative, MOF-808-F5, outperforms the parent MOF-808, achieving recovery rates of 92% for propanal, 67% for octane, and 79% for toluene at 95% relative humidity. Density functional theory revealed that the most significant enhancements in binding enthalpy occur at the weakest adsorption sites of the parent MOF-808. The strategy described herein not only enhances VOC selectivity but also dramatically increases the overall performance of the MOF, underscoring the power of integrating modeling and experimental validation in the development of advanced materials for breath analysis.

A lead-optimized strategy identified an amine functionalized MOF for SF 6 capture at trace concentrations. Density functional theory studies show that the amino group on the linker lowers the pore binding site energy for effective SF 6 capture.

The rising global demand for lanthanides (Ln) necessitates recycling and separation strategies. Due to their similar chemical and physical properties, separating individual Ln from mixtures is challenging. While metal-organic frameworks (MOFs) with nanoscale pores can capture Ln and potentially separate them in aqueous mixtures, no current MOFs are capable of this task. The zirconium (Zr(IV))-based MOFs, UiO-66 and its derivatives, have shown the ability to selectively adsorb Ln from mixtures containing non-Ln ions. Additionally, chemical functionalization of UiO-66 at either the linker or the metal oxo-cluster sites can enhance the selectivity for Ln ions. In this study, we investigated how linker functionalization with electronegative halogen groups impacts the selectivity of Ln adsorption. Our results demonstrate that both UiO-66 and its halogenated derivatives preferentially adsorb heavier Ln over lighter ones, with the degree of selectivity toward heavier Ln correlating with the halogen identity and increasing in the order of F- < Cl- < Br- < I-. Spectroscopic data indicate that Ln adsorbs at the Zr(IV) oxo-cluster sites rather than directly coordinating with the halide groups. Therefore, we attribute the increasing selectivity with increasing halogen size to the changes in the local coordination of Zr oxo-clusters due to halogenation. Concomitantly, electronic structure calculations infer the possibility of stronger interactions between heavier Ln and more polarizable halide atoms. This study highlights the potential of reusable, water-stable MOFs with reactive and tunable nanopores for sustainable Ln separations.

A new metal-organic framework (MOF) with low-valent, σ-bonded OsI-OsI pillars has been prepared using [Os2(ER3)2(μ2-O2CH)2(CO)4] sawhorse complexes (ER3 = {E(C6H4CO2)}3-; E = P or As). This is the first example of the inclusion of OsI into a MOF and is a rare example of a Lewis acidic {M-M}2+ structural motif, which provides broader insights into new synthetic methods for the preparation of MOFs containing catalytically relevant metal species. The isostructural phosphine and arsine MOFs reported here, PCM-201 and AsCM-201, respectively, achieve stabilization of the Os2 cores compared to molecular examples; combined experimental and DFT studies show that the MOF rigidity prevents cleavage of the OsI-OsI bond, which gains stability in the solid state. In contrast, UV irradiation of single crystals at 254 and 365 nm results in a release of CO ligands from OsI centers. The calculated HOMO and LUMO electronic states are found to be markedly different in the MOF versus the free complexes, in addition to significant lattice strain effects, which have important implications for the design of other low-valent MOFs for catalysis.

A new triaryl arsine (Ar3As)-based metal-organic framework (MOF) named AsCM-102 has been prepared by the reaction of As(C6H4-4-CO2H)3 with Co(BF4)2 and 4,4'-bipyridine. AsCM-102 contains pairs of staggered As donors that function as trans-chelators for the facile incorporation of organometallic RhI species via a single crystal-to-single crystal transformation. Coordination of RhI is achieved by soaking crystals in a solution of [Rh(CO)2Cl]2 at 70 °C. The originally closed and offset As2 pockets expand to facilitate the trans-As2 chelation of RhI. The resulting metalated MOF displays trans-[(Ar3As)2Rh(CO)Cln](1-n)+ complexes inside uniquely confined micropore reaction environments. Installation of the As-Rh-As moieties significantly enhances the internal porosity of the MOF. Crystalline RhI-AsCM-102 is an air-stable and recyclable hydroformylation catalyst, which is more active than its phosphine-based analogue. It is also selective toward the formation of iso-aldehydes over n-aldehydes with various C6-C8 olefin feedstocks. By leveraging the absolute atomic coordinates of RhI-AsCM-102 obtained from single-crystal X-ray diffraction analysis, density functional theory (DFT) explains the experimentally observed iso-favored hydroformylation regioselectivity due to pore confinement. RhI-AsCM-102 is resistant toward leaching of As into solution under forcing reaction conditions (40 atm of CO/H2, 70 °C). This work demonstrates the premise that incorporation of organo(arsines) into MOF scaffolds is a safer and more convenient strategy for their deployment in catalysis, by alleviating M-As bond lability and As toxicity issues, which prevents their widespread use in homogeneous catalysis.

Exhaled breath contains trace levels of volatile organic compounds (VOCs) that can reveal information about metabolic processes or pathogens in the body. These molecules can be used for medical diagnosis, but capturing and accurately measuring them is a significant challenge in chemical separations. A highly selective nanoporous sorbent can be used to capture target molecules from a breath sample and preconcentrate them for use in a detector. In this work, we present a combined predictive modeling-experimental validation study in which five Zr-based metal-organic frameworks (MOFs) were identified and tested. These MOFs display good selectivity for a variety of VOCs known to be indicators of viral infections such as influenza and COVID-19. We first used molecular simulation to identify promising MOF candidates that were subsequently synthesized and tested for recovery of a variety of VOCs (toluene, propanal, butanone, octane, acetaldehyde) at concentrations of 20 ppm in humid nitrogen. We show that MOF-818, PCN-777, and UiO-66 have particularly good selectivity for the target molecules in the presence of humidity. These three MOFs each recover around 40-60% of the targets (with the exception of acetaldehyde) at up to 95% relative humidity. MOF-818 recovers 63% of butanone and 60% of toluene at 80% relative humidity. Recovery for acetaldehyde is lower across all MOFs at high humidity, but notably, MOF-808 recovers 90% of acetaldehyde at 60% humidity.

The recovery of sulfur hexafluoride (SF6) at trace concentrations (ppmv) from leaks, exhaust emissions, accidental release, or decommissioned equipment is critically important due to its potential to displace oxygen in confined spaces, posing significant safety risks. However, the inert nature of SF6 presents a persistent challenge for its capture at low concentrations. Metal-organic frameworks (MOFs) have shown promise as adsorbents; yet, rational selection of optimal candidates is not trivial, given the complexities involved in controlling the confined chemical environments that dictate SF6 affinity. Here, a powerful lead-optimized selection process is used to identify a promising amine functionalized MOF for dilute SF6 capture. First, through an optimized grand canonical Monte Carlo approach, the impact of varied pore functional groups on SF6 adsorption was probed. The most promising candidate, Ni(ina-NH2)2, was then synthesized via a novel synthetic method and its enhanced SF6 affinity was validated experimentally. Notably, with an experimental uptake of 2 mmol g-1 at 1 kPa, it was found to be amongst the best performing materials for dilute SF6 capture across all materials reported in the ARCMOF database, which curates over 280 000 of both known and theoretical MOFs. Finally, the mechanism of SF6 adsorption was probed using density functional theory, revealing that inclusion of an amino group on the linker dramatically lowers the average pore binding site energy, thus promoting SF6 capture. This work illustrates that lead-optimized materials selection can serve as a transformative strategy for the rapid and rational identification of materials tailored for specific applications.

In this study, two metal-organic frameworks (MOFs), zirconium (IV)-based MOF-808 and chromium (III)-based MIL-101 were investigated for the selective adsorption of nickel (Ni2+) over cobalt (Co2+) and the role of the nitrogen (N)-containing functional groups was evaluated using pyrazole (PyC) and amine (-NH2). Selective adsorption and adsorption rates were quantified using batch adsorption experiments. The post-reaction MOFs after Co2+ and Ni2+ adsorption were characterized with attenuated total reflectance Fourier transform infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopies to identify the active adsorption sites and to infer the adsorption mechanism. The overall adsorption of Co2+ and Ni2+ by MOF-808 and MIL-101 increased after their surface functionalization with PyC and -NH2. However, selective Ni2+ adsorption was only observed with MOF-808-PyC. The pseudo-second-order model fit to the kinetic adsorption data suggests chemically driven adsorption of Co2+ and Ni2+ onto all examined MOFs. The ATR-FTIR and XPS analyses of MOFs with adsorbed Co2+ and Ni2+ indicate that the N sites in PyC and -NH2 are the reactive sites. ATR-FTIR analyses of aqueous PyC solutions with metal cations show a greater shift in the N-H vibrational band of PyC when interacting with Ni2+ compared to Co2+, which is linked to a stronger interaction between Ni2+ and PyC, resulting in the Ni2+ selectivity by PyC-functionalized MOF-808. We propose that PyC, as a pi-acceptor ligand, exhibits greater affinity for Ni2+ compared to Co2+ due to i) the greater electronegativity of Ni2+ and ii) the greater stability of Ni(2+)complex with PyC ligand based on the Irving-Williams series and ligand field stabilization energy based on the electron configuration differences between Co2+ (3d(7)) and Ni2+ (3d(8)).

Metal-organic frameworks (MOFs) are a class of porous, crystalline materials that have been systematically developed for a broad range of applications. Incorporation of two or more metals into a single crystalline phase to generate heterometallic MOFs has been shown to lead to synergistic effects, in which the whole is oftentimes greater than the sum of its parts. Because geometric proximity is typically required for metals to function cooperatively, deciphering and controlling metal distributions in heterometallic MOFs is crucial to establish structure-function relationships. However, determination of short- and long-range metal distributions is nontrivial and requires the use of specialized characterization techniques. Advancements in the characterization of metal distributions and interactions at these length scales is key to rapid advancement and rational design of functional heterometallic MOFs. This perspective summarizes the state-of-the-art in the characterization of heterometallic MOFs, with a focus on techniques that allow metal distributions to be better understood. Using complementary analyses, in conjunction with computational methods, is critical as this field moves toward increasingly complex, multifunctional systems.

Rare-earth metal-organic frameworks (REMOFs) based on polynuclear metal clusters are an emerging class of materials that have shown promise for CO2 capture and conversion. In this work, copper nanoparticles (CuNPs) were successfully installed on a cluster-based Y(III) MOF to yield a composite material, CuNP-Y-TBAP. The abundance of Cu binding sites on the Y(III) clusters allowed a remarkably high Cu loading to be achieved, and electron microscopy demonstrated that the MOF-supported CuNPs are exceptionally small and monodisperse. CuNP-Y-TBAP was found to be an active heterogeneous catalyst for electrochemical reduction of CO2, yielding CO and CH4 as the primary CO2 reduction products.

Metal-organic frameworks (MOFs) have shown promise for adsorptive separations of metal ions. Herein, MOFs based on highly stable Zr(iv) building units were systematically functionalized with targeted metal binding groups. Through competitive adsorption studies, it was shown that the selectivity for different metal ions was directly tunable through functional group chemistry. The metal ion adsorption selectivities of stable Zr(iv) metal-organic frameworks (MOFs) can be readily tuned via functional group chemistry and control of defect character.

Separating individual lanthanide (Ln) elements in aqueous mixtures is challenging. Ion-selective capture by porous materials, such as metal-organic frameworks (MOFs), is a promising approach. To design ion-selective MOFs, molecular details of the Ln adsorption complexes within the MOFs must be understood. We determine the local coordination environment of lanthanides Nd(III), Gd(III), and Lu(III) adsorbed onto Cr(III)-based terephthalate MOF (Cr-MIL-101) and Zr(IV)-based Universitet in Oslo MOFs (UiO-66 and UiO-68) and their derivatives. In the Cr(III)- and Zr(IV)-based MOFs, Ln adsorb as inner-sphere complexes at the metal oxo clusters, regardless of whether the organic linkers are decorated with amino groups. Missing linkers result in favorable Ln binding sites at oxo clusters; however, Ln can coordinate to metal sites even with linkers in place. MOF functionalization with phosphonate groups led to Ln chemisorption onto these groups, which out-compete metal cluster sites. Ln form monodentate and bidentate and mononuclear and binuclear surface complexes. We conclude that MOFs for ion-selective Ln capture can be designed by a combination of (1) maximizing metal-lanthanide interactions via shared O atoms at the metal oxo cluster sites, where mixed oxo clusters can lead to ion-selective Ln adsorption, and (2) functionalizing MOFs with Ln-selective groups capable of out-completing the metal oxo cluster sites.

High-entropy materials (HEMs) emerged as promising candidates for a diverse array of chemical transformations, including CO2 utilization. However, traditional HEMs catalysts are nonporous, limiting their activity to surface sites. Designing HEMs with intrinsic porosity can open the door toward enhanced reactivity while maintaining the many benefits of high configurational entropy. Here, a synergistic experimental, analytical, and theoretical approach to design the first high-entropy metal-organic frameworks (HEMOFs) derived from polynuclear metal clusters is implemented, a novel class of porous HEMs that is highly active for CO2 fixation under mild conditions and short reaction times, outperforming existing heterogeneous catalysts. HEMOFs with up to 15 distinct metals are synthesized (the highest number of metals ever incorporated into a single MOF) and, for the first time, homogenous metal mixing within individual clusters is directly observed via high-resolution scanning transmission electron microscopy. Importantly, density functional theory studies provide unprecedented insight into the electronic structures of HEMOFs, demonstrating that the density of states in heterometallic clusters is highly sensitive to metal composition. This work dramatically advances HEMOF materials design, paving the way for further exploration of HEMs and offers new avenues for the development of multifunctional materials with tailored properties for a wide range of applications.

Low-valent metal-organic frameworks (LVMOFs) and related materials have gained interest due to their potential applications in heterogeneous catalysis. However, of the few LVMOFs that have been reported, none have shown catalytic activity. Herein, a low-valent metal-organic material constructed from phosphine linkers and Ir-I nodes is reported. This material is effectively a crystalline, insoluble analogue of Vaska's complex. As such, the material reversibly binds O-2 and catalyzes the reductive formation of enamines from amides.

We report the synthesis and characterization of a new series of permanently porous, three-dimensional metal-organic frameworks (MOFs), M-HAF-2 (M = Fe, Ga, or In), constructed from tetratopic, hydroxamate-based, chelating linkers. The structure of M-HAF-2 was determined by three-dimensional electron diffraction (3D ED), revealing a unique interpenetrated hcb-a net topology. This unusual topology is enabled by the presence of free hydroxamic acid groups, which lead to the formation of a diverse network of cooperative interactions comprising metal-hydroxamate coordination interactions at single metal nodes, staggered π-π interactions between linkers, and H-bonding interactions between metal-coordinated and free hydroxamate groups. Such extensive, multimodal interconnectivity is reminiscent of the complex, noncovalent interaction networks of proteins and endows M-HAF-2 frameworks with high thermal and chemical stability and allows them to readily undergo postsynthetic metal ion exchange (PSE) between trivalent metal ions. We demonstrate that M-HAF-2 can serve as versatile porous materials for ionic separations, aided by one-dimensional channels lined by continuously π-stacked aromatic groups and H-bonding hydroxamate functionalities. As an addition to the small group of hydroxamic acid-based MOFs, M-HAF-2 represents a structural merger between MOFs and hydrogen-bonded organic frameworks (HOFs) and illustrates the utility of non-canonical metal-coordinating functionalities in the discovery of new bonding and topological patterns in reticular materials.

Metal-organic framework (MOF)-based membranes have received significant attention as separators for lithium-sulfur (Li-S) batteries because of their high porosities, well-defined and tailored structures, and other tunable features that are desirable for preventing the "shuttle effect" of soluble polysulfides. Because of the insulating nature of most MOFs, composite membranes are generally constructed by a combination of MOFs and electron-conductive materials. In this work, we examine the property-performance relation between MOF-based separators and Li-S batteries by systematically adjusting the electrical conductivity, thickness, and mass loading of the MOF-based composite. Beyond the commonly referenced trapping or blocking ability of MOFs toward polysulfides, we find that by fixing the thickness of the MOF-based composite coating layer (∼40 μm) on a Celgard membrane, the electrical conductivity of the MOF composite layer is of paramount importance compared with the physical/chemical trapping ability of polysulfides. However, the trapping ability of MOFs becomes indispensable when the thickness of the composite layer is small (e.g., ∼20 μm), indicating the synergetic effects of the adsorption and conversion capabilities of the thin composite layer. This work suggests the importance of a holistic design consideration for a MOF-based membrane for long-life and high-energy-density Li-S batteries.

Metal-organic frameworks (MOFs) are crystalline, 2- and 3-dimensional coordination polymers formed by bonding interactions between metals and multitopic organic ligands. These are typically formed using hard Lewis basic organic ligands with high oxidation state metal ions. The use of low-valent metals as structural elements in MOFs is far less common, despite the widespread use of such metals for catalysis, luminescence, and other applications. This Minireview focuses on recent advances in the field of low-valent MOFs and offers a perspective on the future development of these materials.