Protecting air/moisture-sensitive samples using perdeuterated paraffin wax for solid-state NMR experiments under magic-angle spinning.

Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a powerful technique for materials characterization, yet its application to air- and moisture-sensitive materials is often hindered by the difficulty in maintaining an inert environment during magic-angle spinning (MAS). This is particularly true for fast-MAS rotors that do not generally provide tight seals. Herein, we present a generalizable approach employing perdeuterated paraffin waxes-n-icosane-d42 and c-dodecane-d24-as protective embedding media to analyze sensitive organometallic catalysts using SSNMR.

Synthesis and Properties of Poly(vinyl chloride)--polyethylene Multiblock Copolymers through the Hydrodechlorination of PVC with Silylium Ions.

Block copolymers of polyethylene (PE) and polyvinyl chloride (PVC) have remained elusive materials despite PE and PVC being the first and third most produced polymers globally, respectfully. The closest material is chlorinated polyethylene (CPE), which is commonly used as a compatibilizer and is synthesized by functionalizing PE. However, there does not exist a synthetic pathway either from monomers or via the functionalization of PE to yield a polymer that has a controlled chlorine amount and primary structure along the polymer chain.

Understanding the Role of Borohydride Doping in Electrochemical Stability of Argyrodite LiPSCl Solid-State Electrolyte.

This work elucidates the mechanism by which lithium borohydride (LiBH) doping into argyrodite-type LiPSCl (LBH-LPSCl) solid-state electrolyte (SSE) enhances electrochemical stability. State-of-the-art electrochemical performance is achieved with 5 wt% borohydride. Symmetric cells achieve critical current density (CCD) of 7.

Surface Protected Organozirconium Catalyzes C─H Alumination of Saturated Hydrocarbons.

Surface grafted organozirconium catalyzes C─H/Et─Al exchange reactions, involving saturated hydrocarbons and AlEt, to afford organoaluminum compounds and ethane. The Zr(OBu)@SiO-AlO (1) catalyst contains monopodal ≡SiO─Zr(OBu) and only a few residual silanols (<5%). Nonetheless, these silanols are the Achille's heel of 1, providing a pathway for surface and catalyst degradation during catalysis, limiting the alkylaluminum yield and catalyst turnover.

Ultra-Confined Environments May Restrict the Possible Configurations of Supported Metal Complexes.

The rotation frequencies of amido ligands are highly sensitive to the electronic structure of transition metal complexes and have been used to study ligand donor properties. While attempting to study the donor properties of silanolate ligands in a silica-supported Cr complex, we observed highly restricted motions due to the added steric hindrance from the support, with only approximately half of the amides rotating on a 50 ms time scale. Surprisingly, when the same species is grafted into narrow 2.

In Silico Design of Methyl-Driven Overhauser Dynamic Nuclear Polarization Agents.

Overhauser effect (OE) dynamic nuclear polarization (DNP) has drawn attention owing to its enhanced performance at ultrahigh magnetic fields. The lack of design principles has, nevertheless, limited the development of OE polarizing agents when compared to those used for cross-effect DNP. We measured the F OE DNP performance of a series of CF-functionalized Blatter-type radicals.

Preferred Orientation of a Physisorbed Molecular Catalyst and Implications for Selectivity.

Confinement effects in stereoselective catalysis have been the topic of prolonged inquiry. Results have been largely mixed, with confinement having been reported to both enhance and degrade selectivity. Our ability to understand the surface's impact on catalytic mechanisms, and thus selectivity, has been severely hindered by the low level of details commonly seen in the structures of supported metal complexes.

Fluoropolymer Composites from Partially Perfluoroalkylated Waste Polyethylene.

Chemically modified plastics have emerged as practical solutions to plastic waste increases. The inherent novelty of decorating polymer chains with chemical functionality results in distinct properties that expand the available application space. Nevertheless, developing designer materials for specific applications beyond compatibilization or mild property enhancement is difficult due to the synergistic effects of both the polar functionality imparted and the parent materials' intrinsic properties.

A Broad-Spectrum Catalyst for Aliphatic Polymer Breakdown.

Thermolysis of the well-defined aluminum fluoroalkoxide supported on silica (≡SiOAl(OC(CF))(O(Si≡)), , 0.20 mmol g) at 200 °C forms a fluorinated amorphous silica-alumina (F-ASA) containing a distribution of Al(IV), Al(V), and Al(VI) sites that maintain relatively strong Lewis acidity. Small amounts of Brønsted sites are also present in F-ASA.

Well-defined Pt(0) heterogeneous hydrosilylation catalysts supported by a surface bound phosphenium ligand.

Single atom, low valent transition metals are important for heterogeneous catalysis but are challenging to generate and stabilize in a well-defined manner. Herein, we explored the functionalization of silica with well-defined N-heterocyclic phosphenium (NHP) ions to heterogenize low-valent metals. The surface electrostatically bound [NHP] ions coordinate to Pt(0) precursors, resulting in well-defined, chemisorbed [(NHP)Pt(0)L] sites.

Perspectives on the Dynamic Nuclear Polarization Mechanisms of Monoradicals: Overhauser Effect or Thermal Mixing?

This mini-review summarizes the evolving debate regarding the origins of the absorptive features seen in the dynamic nuclear polarization (DNP) spectra of certain monoradicals when they are irradiated at their electron Larmor frequency. This feature has drawn attention due to its reverse scaling with respect to the magnetic field strength and potential for high-field DNP. Two competing hypotheses have been introduced to explain the DNP feature based on (1) the Overhauser effect and low-temperature molecular dynamics and (2) radical clustering and a thermal mixing mechanism.

Highly sensitive measurements of methylene dynamics with a frequency-selective double-quantum sideband method.

Probing the fast dynamics of surface sites using NMR spectroscopy is highly challenging owing to the sites' high dilution and the difficulties often associated with isotopic enrichment. Intra-CHH-H dipolar couplings are ideal probes of motions given that they only involve H's and the tensor has a well-defined size and orientation. We introduce a frequency-selective variant of the double-quantum sideband method to measure like-spin H-H dipolar coupling constants.

Removal of Homogeneous Broadening from H-Detected Multidimensional Solid-State NMR Spectra.

H-detected magic-angle spinning (MAS) NMR experiments have revolutionized the NMR studies of biological and inorganic solids by providing unparalleled sensitivity and resolution. Despite these gains, homogeneous broadening, originating from the incomplete removal of homonuclear dipolar interactions under fast MAS, remains highly prevalent and limits the achievable resolution. In direct analogy to super-resolution microscopy methods, we show that resolution beyond that currently achievable by fast MAS alone can be obtained by experiment-driven deconvolution.

Hydrogen Isotope Labeling of Pharmaceuticals Via Dual Hydrogen Isotope Exchange Pathways Using CdS Quantum Dot Photocatalyst.

Isotopic labeling is a powerful technique extensively used in the pharmaceutical industry. By tracking isotope-labeled molecules, researchers gain unique and invaluable insights into the pharmacokinetics and pharmacodynamics of new drug candidates. Hydrogen isotope labeling is particularly important as hydrogen is ubiquitous in organic molecules in biological systems, and it can be introduced effectively through late-stage hydrogen isotope exchange (HIE).

Selective O-labeling of silica.

The addition of OH to silica at room temperature leads to spontaneous hydroxyl oxygen exchange and the selective isotopic enrichment of silanols, as observed using and O NMR. The discovery that silanols are labile alters our understanding of the chemistry of silica surfaces.

Observing the Surface Termination of LaScO Perovskite Using Solid-State Nuclear Magnetic Resonance.

Materials with well-defined surfaces are drawing increased attention for the design of bespoke catalysts and nanomaterials. Gaining a detailed understanding of the surfaces of these materials is an important challenge, which is often complicated by surface polymorphism and dynamic restructuring. We introduce the use of surface-enhanced NMR spectroscopy for the observation of such surfaces, focusing on LaScO as an example.

Comparison of methods for the NMR measurement of motionally averaged dipolar couplings.

Motionally averaged dipolar couplings are an important tool for understanding the complex dynamics of catalysts, polymers, and biomolecules. While there is a plethora of solid-state NMR pulse sequences available for their measurement, in can be difficult to gauge the methods' strengths and weaknesses. In particular, there has not been a comprehensive comparison of their performance in natural abundance samples, where H homonuclear dipolar couplings are important and the use of large MAS rotors may be required for sensitivity reasons.

Elimination of homogeneous broadening in H solid-state NMR.

H solid-state NMR spectra are plagued by low resolution, necessitating the use of complex pulse sequences or specialized equipment. We introduce a new resolution enhancement method, inspired by super-resolution microscopy, that uses a 2D Hahn-echo experiment to constrain deconvolution. The result is an effective doubling of the MAS frequency.

Silicon Nitride Surface Enabled Propane Dehydrogenation Catalyzed by Supported Organozirconium.

Mesoporous silicon nitride (SiN) is a nontraditional support for the chemisorption of organometallic complexes with the potential for enhancing catalytic activity through features such as the increased Lewis basicity of nitrogen for heterolytic bond activation, increased ligand donor strength, and metal-ligand orbital overlap. Here, tetrabenzyl zirconium (ZrBn) was chemisorbed on SiN, and the resulting supported organometallic species was characterized by Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Dynamic Nuclear Polarization-enhanced Solid State Nuclear Magnetic Resonance (DNP-SSNMR), and X-ray Absorption Spectroscopy (XAS). Based on the hypothesis that the nitride might enable facile heterolytic C-H bond activation along the Zr-N bond, this material was found to be a highly active (1.

Automatic fitting of multiple-field solid-state NMR spectra.

The NMR lineshapes produced by half-integer quadrupolar nuclei are sensitive to 11 distinct fit parameters per inequivalent site. To date, automatic fitting routines have failed to replace manual parameter insertion and evaluation due to the importance of local minima and the need for fitting multiple-field magic-angle spinning (MAS) and static spectra simultaneously. Herein we introduce a new tool, AMES-Fit (Automatic Multiple Experiment Simulation and Fitting), to automatically find the global best-fit simulation parameters for a series of multiple-field NMR lineshapes.

On the use of NMR distance measurements for assessing surface site homogeneity.

The past few decades have seen tremendous growth in the area of single-site heterogeneous catalysis, which aims to combine the best aspects of homogeneous and heterogeneous catalysis, namely molecular-level site control and ease of separation/recycling. Despite this, we still do not have a means of assessing site homogeneity and whether the produced catalyst is indeed a "single-site". Recent developments have enabled the use of NMR-based distance measurements to determine the conformations and configurations of surface sites, leading to the question whether such measurements can be used to distinguish materials containing either single or multiple surface sites with otherwise indistinguishable NMR properties.

Are the Brønsted acid sites in amorphous silica-alumina bridging?

Competing models exist to explain the differences in the activity of zeolites and amorphous silica-aluminas. Some postulate that silica-alumina contains dilute zeolitic bridging acid sites, while others favor a pseudo-bridging silanol model. We employed a selective isotope labeling strategy to assess the existence of Si-O(H)-Al bonds using NMR-based distance measurements.

Make Selenium Reactive Again: Activating Elemental Selenium for Synthesis of Metal Selenides Ranging from Nanocrystals to Large Single Crystals.

The inertness of elemental selenium is a significant obstacle in the synthesis of selenium-containing materials at low reaction temperatures. Over the years, several recipes have been developed to overcome this hurdle; however, most of the methods are associated with the use of highly toxic, expensive, and environmentally harmful reagents. As such, there is an increasing demand for the design of cheap, stable, and nontoxic reactive selenium precursors usable in the low-temperature synthesis of transition metal selenides with vast applications in nanotechnology, thermoelectrics, and superconductors.