Multicomponent metal-organic framework membranes for advanced functional composites.

The diverse chemical and structural properties of metal-organic frameworks (MOFs) make them attractive for myriad applications, but their native powder form is limiting for industrial implementation. Composite materials of MOFs hold promise as a means of exploiting MOF properties in engineered forms for real-world applications. While interest in MOF composites is growing, research to date has largely focused on utilization of single MOF systems. The vast number of different MOF structures provides ample opportunity to mix and match distinct MOF species in a single composite to prepare multifunctional systems. In this work, we describe the preparation of three types of multi-MOF composites with poly(vinylidene fluoride) (PVDF): (1) co-cast MOF MMMs, (2) mixed MOF MMMs, and (3) multilayer MOF MMMs. Finally, MOF MMMs are explored as catalytic membrane reactors for chemical transformations

A Thorium Metal-Organic Framework with Outstanding Thermal and Chemical Stability.

A new thorium metal-organic framework (MOF), Th(OBA)2 , where OBA is 4,4'-oxybis(benzoic) acid, has been synthesized hydrothermally in the presence of a range of nitrogen-donor coordination modulators. This Th-MOF, described herein as GWMOF-13, has been characterized by single-crystal and powder X-ray diffraction, as well as through a range of techniques including gas sorption, thermogravimetric analysis (TGA), solid-state UV/Vis and luminescence spectroscopy. Single-crystal X-ray diffraction analysis of GWMOF-13 reveals an interesting, high symmetry (cubic Ia 3 ‾ d) structure, which yields a novel srs-a topology. Most notably, TGA analysis of GWMOF-13 reveals framework stability to 525 °C, matching the thermal stability benchmarks of the UiO-66 series MOFs and zeolitic imidazolate frameworks (ZIFs), and setting a new standard for thermal stability in f-block based MOFs

Probing Hydrogen and Halogen-Oxo Interactions in Uranyl Coordination Polymers:A Combined Crystallographic and Computational Study

The syntheses and crystal structures of four compounds containing the UO22+ cation and either benzoic acid (1), m-chlorobenzoic acid (2), m-bromobenzoic acid (3), or m-iodobenzoic acid (4) are described and the vibrational spectroscopic properties for compounds 3 and 4 are reported. Single crystal X-ray diffraction analysis of these materials shows that uranyl oxo atoms are engaged in non-covalent assembly via either hydrogen (1 and 2) or halogen bonding (3 and 4) interactions. The halogen bonding in compounds 3 and 4 is notable as the crystallographic metric percentage of the sum of the van der Waals radii indicates these interactions are of similar strength. Characteristics of the halogen-oxo interactions of 3 and 4 were probed via Raman and infrared spectroscopy, which revealed significant differences in stretching frequency values for the two compounds. Additionally, compounds 3 and 4 were characterized via quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analysis, which indicated that the I-oxo interaction in 4 is likely the stronger of the two interactions, with differences between the two interactions resulting from both inductive effects and halogen polarizability

How to Bend the Uranyl Cation via Crystal Engineering

Bending the linear uranyl (UO22+) cation represents both a significant challenge and opportunity within the field of actinide hybrid materials. As part of related efforts to engage the nominally terminal oxo atoms of uranyl cation in noncovalent interactions, we synthesized a new uranyl complex, [UO2(C12H8N2)2(C7H2Cl3O2)2]·2H2O (complex 2), that featured both deviations from equatorial planarity and uranyl linearity from simple hydrothermal conditions. Based on this complex, we developed an approach to probe the nature and origin of uranyl bending within a family of hybrid materials, which was done via the synthesis of complexes 1–3 that display significant deviations from equatorial planarity and uranyl linearity (O–U–O bond angles between 162° and 164°) featuring 2,4,6-trihalobenzoic acid ligands (where Hal = F, Cl, and Br) and 1,10-phenanthroline, along with nine additional “nonbent” hybrid materials that either coformed with the “bent” complexes (4–6) or were prepared as part of complementary efforts to understand the mechanism(s) of uranyl bending (7–12). Complexes were characterized via single crystal X-ray diffraction and Raman, infrared (IR), and luminescence spectroscopy, as well as via quantum chemical calculations and density-based quantum theory of atoms in molecules (QTAIM) analysis. Looking comprehensively, these results are compared with the small library of bent uranyl complexes in the literature, and herein we computationally demonstrate the origin of uranyl bending and delineate the energetics behind this process

Exploring the promotion of synthons of choice: halogen bonding in molecular lanthanide complexes characterized via X-ray diffraction, luminescence spectroscopy, and magnetic measurements

Promotion of a synthon of choice for the non-covalent assembly of lanthanide tectons represents both a noteworthy challenge and opportunity within LnIII hybrid materials. We have developed a system, wherein some control can be exercised over supramolecular assembly and, as part of continued efforts to improve this process we have generated a family of ten new lanthanide (Ln = Sm3+ – Lu3+) 2,4,6-trichlorobenzoic acid-1,10-phenanthroline molecular complexes. Delineation of criteria for promoting assembly via halogen based interactions was introduced previously and is refined herein based on the characterization of complexes 1–10 via single-crystal X-ray diffraction. Direct comparison of means of supramolecular assembly for 1–10 with isostructural Ln-p-chlorobenzoic acid-1,10-phenanthroline analogues verifies that increasing the number of halogen atoms at the periphery of a tecton is one route that increases the frequency of halogen bonding interactions. Additionally, solid-state visible and near-IR photoluminescence and luminescent lifetime data were collected for complexes 1 (Sm3+), 2 (Eu3+), 4 (Tb3+), 5 (Dy3+), 6 (Ho3+), 7 (Er3+), and 9 (Yb3+) and characteristic emission was observed for all complexes except 6. Further, direct current magnetic susceptibility measurements were carried out for complexes 5 (Dy3+) and 7 (Er3+), and two slow magnetic relaxation processes were characterized using alternating current magnetic susceptibility measurements for 5

Metal-Organic Framework Polymer Hybrid Materials for Chemical Warfare Agent Degradation

Since first discovered some two decades ago, metal-organic frameworks (MOFs) have shown interesting properties with regard to storage, separation, and catalysis applications. While MOFs have shown promise in these arenas over the years, a major shortcoming of these materials is their inherently crystalline form factor which hinders their applicational. To circumvent this issue, we have turned to the hybridization of MOFs with polymers in an effort to form a material that has the desired properties of the MOF and the flexibility of the polymer. In particular, we seek to develop novel textile based (nylon based or spray coated) MOF-polymer hybrid materials that are catalytically active against harmful organophosphorus chemical warfare agents (CWAs). Chapter 2 describes the synthesis of a MOF-nylon hybrid material through and interfacial postsynthetic polymerization (PSP) method. The hybrid material contains 29 weight percent MOF and shows catalytic activity against a CWA simulant. Importantly, the covalent MOF-nylon material displays about a seven-fold increase in activity compared to physically mixed controls. In Chapter 3, we screened a wide range of MOFs with varying organic functional groups to establish structure activity relationships (SAR) between MOF functional groups and CWA simulant degradation. The Zr-based MOF UiO-66 (UiO = University of Oslo) was synthesized with either mixed ligand functional groups or halogenated functional groups. We determined that the mixed ligand approach improves CWA activity by three-fold whereas the UiO-66-Iodine MOF displays a fourfold increase in activity. Through theoretical calculations, the increased activity in UiO-66-I was determined to be an artifact of halogen bonding with the CWA simulant. In Chapter 4, we combined the approaches from Chapter 2 and 3, by using the commonly known pseudohalogen isothiocyanate (NCS) functional group in UiO-66 to improve the catalytic activity against CWAs and covalent PSP sites. The UiO-66-NCS MOF was synthesized via postsynthetic modification (PSM) and displayed a ~20 fold increase in activity compared to the presynthetic MOF. More importantly, using amine terminated polypropylene oxides, MOF-polymer material was formed, and spray coated onto textile fibers. This material showed great durability and catalytic activity compared to physically mixed controls. Chapter 5 describes the room temperature synthesis of the commonly used UiO-66 MOF as well as a few functional groups derivatives. Starting from a UiO-66-F4 MOF with relatively labile ligands, postsynthetic exchange (PSE) with four different MOF ligands at room temperature in aqueous conditions was performed with almost complete ligand exchange. These MOFs were thoroughly characterized after PSE and maintained desired properties such as crystallinity and particle size or shape

Postsynthetic Modification: An Enabling Technology for the Advancement of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are a class of porous materials with immense chemical tunability derived from their organic and inorganic building blocks. Presynthetic approaches have been used to construct tailor-made MOFs, but with a rather restricted functional group scope limited by the typical MOF solvothermal synthesis conditions. Postsynthetic modification (PSM) of MOFs has matured into an alternative strategy to broaden the functional group scope of MOFs. PSM has many incarnations, but two main avenues include (1) covalent PSM, in which the organic linkers of the MOF are modified with a reagent resulting in new functional groups, and (2) coordinative PSM, where organic molecules containing metal ligating groups are introduced onto the inorganic secondary building units (SBUs) of the MOF. These methods have evolved from simple efforts to modifying MOFs to demonstrate proof-of-concept, to becoming key synthetic tools for advancing MOFs for a range of emerging applications, including selective gas sorption, catalysis, and drug delivery. Moreover, both covalent and coordinative PSM have been used to create hierarchal MOFs, MOF-based porous liquids, and other unusual MOF materials. This Outlook highlights recent reports that have extended the scope of PSM in MOFs, some seminal reports that have contributed to the advancement of PSM in MOFs, and our view on future directions of the field

Postsynthetic Modification: An Enabling Technology for the Advancement of Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are a class of porous materials with immense chemical tunability derived from their organic and inorganic building blocks. Presynthetic approaches have been used to construct tailor-made MOFs, but with a rather restricted functional group scope limited by the typical MOF solvothermal synthesis conditions. Postsynthetic modification (PSM) of MOFs has matured into an alternative strategy to broaden the functional group scope of MOFs. PSM has many incarnations, but two main avenues include (1) covalent PSM, in which the organic linkers of the MOF are modified with a reagent resulting in new functional groups, and (2) coordinative PSM, where organic molecules containing metal ligating groups are introduced onto the inorganic secondary building units (SBUs) of the MOF. These methods have evolved from simple efforts to modifying MOFs to demonstrate proof-of-concept, to becoming key synthetic tools for advancing MOFs for a range of emerging applications, including selective gas sorption, catalysis, and drug delivery. Moreover, both covalent and coordinative PSM have been used to create hierarchal MOFs, MOF-based porous liquids, and other unusual MOF materials. This Outlook highlights recent reports that have extended the scope of PSM in MOFs, some seminal reports that have contributed to the advancement of PSM in MOFs, and our view on future directions of the field

ReI Tricarbonyl Complexes as Coordinate Covalent Inhibitors for the SARS-CoV-2 Main Cysteine Protease.

Since its outbreak, the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) has impacted the quality of life and cost hundreds-of-thousands of lives worldwide. Based on its global spread and mortality, there is an urgent need for novel treatments which can combat this disease. To date, the 3-chymotrypsin-like protease (3CLpro ), which is also known as the main protease, is considered among the most important pharmacological targets. The vast majority of investigated 3CLpro inhibitors are organic, non-covalent binders. Herein, the use of inorganic, coordinate covalent binders is proposed that can attenuate the activity of the protease. ReI tricarbonyl complexes were identified that demonstrate coordinate covalent enzymatic inhibition of 3CLpro . Preliminary studies indicate the selective inhibition of 3CLpro over several human proteases. This study presents the first example of metal complexes as inhibitors for the 3CLpro cysteine protease