Data_Sheet_1_Restricting Polyoxometalate Movement Within Metal-Organic Frameworks to Assess the Role of Residual Water in Catalytic Thioether Oxidation Using These Dynamic Composites.docx

Comprised of high valent metal centers connected via oxide bonds, polyoxometalates (POMs) have a rich history in redox reactions. These discrete metal oxide clusters often are immobilized on heterogeneous supports to increase stability and allow for recyclability for catalytic reactions. One such support is the metal-organic framework (MOF), NU-1000. When POMs are installed into NU-1000, they are first sited in the mesoporous channel. Upon application of heat and removal of some physisorbed water, the POMs migrate to the microporous channel, where some active sites are blocked by the MOF linkers, resulting in lowered catalytic activity. To restrict this movement from the mesopore, we report here the use of two MOFs, naphthalene dicarboxylate-modified NU-1000 (NU-1000-NDC) and NU-1008, as supports for the Keggin-type polyoxometalate (POM), H3PW12O40. Upon the application of heat, these frameworks were found to hinder or prevent the movement of the POM between channels by blocking the aperture(s) connecting the mesoporous and microporous channels. The composite POM@MOF materials were used for the oxidation of a mustard gas simulant, 2-cholorethyl ethyl sulfide, using H2O2 as the oxidant. The POM@MOF catalysts exhibit enhanced reactivity when compared to the POM or MOF alone, more than doubling the initial rates. The activity trend in PW12@NU-1000-NDC matched that in PW12@NU-1000, where the scCO2-activated sample poised the POM in the mesopores to give greater substrate accessibility and enhance the reaction rate compared to the heated sample where the POMs are poised in the micropores. Contrary to these observed trends, PW12@NU-1008 prohibits POM migration and performs superior when water has been removed at elevated temperatures as the active sites are more accessible in the mesoporous channel.</p

Single-Atom-Based Vanadium Oxide Catalysts Supported on Metal–Organic Frameworks: Selective Alcohol Oxidation and Structure–Activity Relationship

We report the syntheses, structures, and oxidation catalytic activities of a single-atom-based vanadium oxide incorporated in two highly crystalline MOFs, Hf-MOF-808 and Zr-NU-1000. These vanadium catalysts were introduced by a postsynthetic metalation, and the resulting materials (Hf-MOF-808-V and Zr-NU-1000-V) were thoroughly characterized through a combination of analytic and spectroscopic techniques including single-crystal X-ray crystallography. Their catalytic properties were investigated using the oxidation of 4-methoxybenzyl alcohol under an oxygen atmosphere as a model reaction. Crystallographic and variable-temperature spectroscopic studies revealed that the incorporated vanadium in Hf-MOF-808-V changes position with heat, which led to improved catalytic activity

Single-Atom-Based Vanadium Oxide Catalysts Supported on Metal–Organic Frameworks: Selective Alcohol Oxidation and Structure–Activity Relationship

We report the syntheses, structures, and oxidation catalytic activities of a single-atom-based vanadium oxide incorporated in two highly crystalline MOFs, Hf-MOF-808 and Zr-NU-1000. These vanadium catalysts were introduced by a postsynthetic metalation, and the resulting materials (Hf-MOF-808-V and Zr-NU-1000-V) were thoroughly characterized through a combination of analytic and spectroscopic techniques including single-crystal X-ray crystallography. Their catalytic properties were investigated using the oxidation of 4-methoxybenzyl alcohol under an oxygen atmosphere as a model reaction. Crystallographic and variable-temperature spectroscopic studies revealed that the incorporated vanadium in Hf-MOF-808-V changes position with heat, which led to improved catalytic activity

Exploring the Role of Hexanuclear Clusters as Lewis Acidic Sites in Isostructural Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have been extensively investigated as Lewis acidic catalysts for a variety of reactions. However, the identity and nature of the MOF nodes in the catalysis remain ill-defined. Herein, a series of isostructural MOFs (M-NU-1008), with M being hexanuclear clusters of transition metals (Zr and Hf), a lanthanide (Ce), or an actinide (Th), were successfully synthesized and evaluated as Lewis acid catalysts, and CO2 cycloaddition of styrene oxide was used as a test reaction. Superior catalytic activity was observed with Ce-NU-1008 over the other M6-based MOFs. In addition to the different Lewis acidities among the metals in the four M-NU-1008, the dissociation of terminal water molecules from the M6 clusters before exposing the Lewis acidic metal sites was found to vary between the MOFs, as supported by variable-temperature diffuse reflectance infrared Fourier transform spectroscopy studies. In the MOFs where water dissociation from the metal nodes readily occurs, the catalytic activity is higher than the MOFs where water is bound more strongly. Upon further investigation, Hf-NU-1008-dehy with terminal water partially removed was found to exhibit enhanced activity compared to the as-prepared catalyst

Exploring the Role of Hexanuclear Clusters as Lewis Acidic Sites in Isostructural Metal–Organic Frameworks

Metal–organic frameworks (MOFs) have been extensively investigated as Lewis acidic catalysts for a variety of reactions. However, the identity and nature of the MOF nodes in the catalysis remain ill-defined. Herein, a series of isostructural MOFs (M-NU-1008), with M being hexanuclear clusters of transition metals (Zr and Hf), a lanthanide (Ce), or an actinide (Th), were successfully synthesized and evaluated as Lewis acid catalysts, and CO2 cycloaddition of styrene oxide was used as a test reaction. Superior catalytic activity was observed with Ce-NU-1008 over the other M6-based MOFs. In addition to the different Lewis acidities among the metals in the four M-NU-1008, the dissociation of terminal water molecules from the M6 clusters before exposing the Lewis acidic metal sites was found to vary between the MOFs, as supported by variable-temperature diffuse reflectance infrared Fourier transform spectroscopy studies. In the MOFs where water dissociation from the metal nodes readily occurs, the catalytic activity is higher than the MOFs where water is bound more strongly. Upon further investigation, Hf-NU-1008-dehy with terminal water partially removed was found to exhibit enhanced activity compared to the as-prepared catalyst

Zirconium-Based Metal–Organic Frameworks for the Removal of Protein-Bound Uremic Toxin from Human Serum Albumin

Uremic toxins often accumulate in patients with compromised kidney function, like those with chronic kidney disease (CKD), leading to major clinical complications including serious illness and death. Sufficient removal of these toxins from the blood increases the efficacy of hemodialysis, as well as the survival rate, in CKD patients. Understanding the interactions between an adsorbent and the uremic toxins is critical for designing effective materials to remove these toxic compounds. Herein, we study the adsorption behavior of the uremic toxins, p-cresyl sulfate, indoxyl sulfate, and hippuric acid, in a series of zirconium-based metal–organic frameworks (MOFs). The pyrene-based MOF, NU-1000, offers the highest toxin removal efficiency of all the MOFs in this study. Other Zr-based MOFs possessing comparable surface areas and pore sizes to NU-1000 while lacking an extended aromatic system have much lower toxin removal efficiency. From single-crystal X-ray diffraction analyses assisted by density functional theory calculations, we determined that the high adsorption capacity of NU-1000 can be attributed to the highly hydrophobic adsorption sites sandwiched by two pyrene linkers and the hydroxyls and water molecules on the Zr6 nodes, which are capable of hydrogen bonding with polar functional groups of guest molecules. Further, NU-1000 almost completely removes p-cresyl sulfate from human serum albumin, a protein that these uremic toxins bind to in the body. These results offer design principles for potential MOFs candidates for uremic toxin removal

Increased Electrical Conductivity in a Mesoporous Metal–Organic Framework Featuring Metallacarboranes Guests

Nickel­(IV) bis­(dicarbollide) is incorporated in a zirconium-based metal–organic framework (MOF), NU-1000, to create an electrically conductive MOF with mesoporosity. All the nickel bis­(dicarbollide) units are located as guest molecules in the microporous channels of NU-1000, which permits the further incorporation of other active species in the remaining mesopores. For demonstration, manganese oxide is installed on the nodes of the electrically conductive MOF. The electrochemically addressable fraction and specific capacitance of the manganese oxide in the conductive framework are more than 10 times higher than those of the manganese oxide in the parent MOF

Zirconium-Based Metal–Organic Frameworks for the Removal of Protein-Bound Uremic Toxin from Human Serum Albumin

Uremic toxins often accumulate in patients with compromised kidney function, like those with chronic kidney disease (CKD), leading to major clinical complications including serious illness and death. Sufficient removal of these toxins from the blood increases the efficacy of hemodialysis, as well as the survival rate, in CKD patients. Understanding the interactions between an adsorbent and the uremic toxins is critical for designing effective materials to remove these toxic compounds. Herein, we study the adsorption behavior of the uremic toxins, p-cresyl sulfate, indoxyl sulfate, and hippuric acid, in a series of zirconium-based metal–organic frameworks (MOFs). The pyrene-based MOF, NU-1000, offers the highest toxin removal efficiency of all the MOFs in this study. Other Zr-based MOFs possessing comparable surface areas and pore sizes to NU-1000 while lacking an extended aromatic system have much lower toxin removal efficiency. From single-crystal X-ray diffraction analyses assisted by density functional theory calculations, we determined that the high adsorption capacity of NU-1000 can be attributed to the highly hydrophobic adsorption sites sandwiched by two pyrene linkers and the hydroxyls and water molecules on the Zr6 nodes, which are capable of hydrogen bonding with polar functional groups of guest molecules. Further, NU-1000 almost completely removes p-cresyl sulfate from human serum albumin, a protein that these uremic toxins bind to in the body. These results offer design principles for potential MOFs candidates for uremic toxin removal

Increased Electrical Conductivity in a Mesoporous Metal–Organic Framework Featuring Metallacarboranes Guests

Nickel­(IV) bis­(dicarbollide) is incorporated in a zirconium-based metal–organic framework (MOF), NU-1000, to create an electrically conductive MOF with mesoporosity. All the nickel bis­(dicarbollide) units are located as guest molecules in the microporous channels of NU-1000, which permits the further incorporation of other active species in the remaining mesopores. For demonstration, manganese oxide is installed on the nodes of the electrically conductive MOF. The electrochemically addressable fraction and specific capacitance of the manganese oxide in the conductive framework are more than 10 times higher than those of the manganese oxide in the parent MOF