A combined solid-state H, C, O NMR and periodic DFT study of hyperfine coupling tensors in paramagnetic copper(II) compounds.

We report solid-state H, C, and O NMR determination of hyperfine coupling tensors (A-tensors) in several paramagnetic Cu(II) (d, S = 1/2) complexes: trans-Cu(DL-Ala)·HO, Cu([1-C]acetate)·HO, Cu([2-C]acetate)·HO, and Cu(acetate)·HO. Using these new experimental results and some A-tensor data available in the literature for trans-Cu(L-Ala) and KCuCl·2HO, we were able to examine the accuracy of A-tensor computation from a periodic DFT method implemented in the BAND program. We evaluated A-tensors on H (I = 1/2), C (I = 1/2), N (I = 1), O (I = 5/2), K (I = 3/2), Cl (I = 3/2), and Cu (I = 3/2) nuclei over a range spanning more than 3 orders of magnitude.

H/O Chemical Shift Waves in Carboxyl-Bridged Hydrogen Bond Networks in Organic Solids.

We report solid-state H and O NMR results for four O-labeled organic compounds each containing an extensive carboxyl-bridged hydrogen bond (CBHB) network in the crystal lattice: tetrabutylammonium hydrogen di-[O]salicylate (), [O]quinolinic acid (), [O]dinicotinic acid (), and [O]Gly/[O]Gly·HCl cocrystal (). The H isotropic chemical shifts found for protons involved in different CBHB networks are between 8.2 and 20.

Understanding Cu(i) local environments in MOFs Cu NMR spectroscopy.

The field of metal-organic frameworks (MOFs) includes a vast number of hybrid organic and inorganic porous materials with wide-ranging applications. In particular, the Cu(i) ion exhibits rich coordination chemistry in MOFs and can exist in two-, three-, and four-coordinate environments, which gives rise to many structural motifs and potential applications. Direct characterization of the structurally and chemically important Cu(i) local environments is essential for understanding the sources of specific MOF properties.

Experimental Evidence for Non-Fermi-Contact J Coupling Across Chalcogen Bonds in Ionic Salt Cocrystal Polymorphs.

A pair of novel polymorphic ionic cocrystals of 3,4-dicyanotelluradiazole and tetraphenylphosphonium bromide are synthesized and are characterized by single-crystal XRD. Strong and directional non-covalent chalcogen bonds (ChB) between Te and Br are analyzed via solid-state NMR to reveal large and anisotropic J(Te,Br) coupling tensors, providing unequivocal evidence for non-Fermi contact contributions across ChBs. Along with large Br quadrupolar couplings for the Br anions, these data provide new tools to characterize chalcogen bonds and to differentiate between ChB polymorphs.

Cold, Hot, Dry, and Wet: Locations and Dynamics of CO and HO Co-Adsorbed in an Ultramicroporous MOF.

Climate change from anthropogenic carbon dioxide (CO) emissions poses a severe threat to society. A variety of mitigation strategies currently include some form of CO capture. Metal-organic frameworks (MOFs) have shown great promise for carbon capture and storage, but several issues must be solved before feasible widespread adoption is possible.

Overcoming challenges in Zn NMR: a new strategy of signal enhancement for MOF characterization.

Zn solid-state NMR suffers from low sensitivity, limiting its ability to probe the Zn surroundings in MOFs. We report a breakthrough in overcoming challenges in Zn NMR. Combining new cryogenic MAS probe technology and performing NMR experiments at a high magnetic field results in remarkable signal enhancement, yielding enhanced information for MOF characterization.

Solid-state O NMR study of α-d-glucose: exploring new frontiers in isotopic labeling, sensitivity enhancement, and NMR crystallography.

We report synthesis and solid-state O NMR characterization of α-d-glucose for which all six oxygen atoms are site-specifically O-labeled. Solid-state O NMR spectra were recorded for α-d-glucose/NaCl/HO (2/1/1) cocrystals under static and magic-angle-spinning (MAS) conditions at five moderate, high, and ultrahigh magnetic fields: 14.1, 16.

Multinuclear solid-state NMR: Unveiling the local structure of defective MOF MIL-120.

Metal-organic frameworks (MOFs) are emerging materials with many current and potential applications due to their unique properties. One critical feature is that the physical and chemical properties of MOFs are tunable. One of the methods for tuning MOF properties is to introduce defects by design for desired applications.

Exploring Structural Nuances in Germanium Halide Perovskites Using Solid-State Ge and Cs NMR Spectroscopy.

Metal halide perovskites remain top candidates for higher-performance photovoltaic devices, but concerns about leading lead-based materials remain. Ge perovskites remain understudied for use in solar cells compared to their Sn-based counterparts. In this work, we undertake a combined Ge and Cs solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and density functional theory (DFT) study of the bulk CsGeX (X = Cl, Br, or I) series.

Perspectives of fast magic-angle spinning Rb NMR of organic solids at high magnetic fields.

We report solid-state Rb NMR spectra from two Rb-ionophore complexes obtained with fast magic-angle spinning (MAS) (up to 60 kHz) at 21.1 T. These Rb-ionophore complexes containing macrocycles such as benzo-15-crown-5 and cryptand [2.

Chlorine-35 Solid-State Nuclear Magnetic Resonance Spectroscopy as an Indirect Probe of the Oxidation Number of Tin in Tin Chlorides.

Ultrawideline Cl solid-state nuclear magnetic resonance (SSNMR) spectra of a series of 12 tin chlorides were recorded. The magnitude of the Cl quadrupolar coupling constant () was shown to consistently indicate the chemical state (oxidation number) of the bound Sn center. The chemical state of the Sn center was independently verified by tin Mössbauer spectroscopy.

Ultramicropore Engineering by Dehydration to Enable Molecular Sieving of H by Calcium Trimesate.

The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.

C chemical shift tensors in MOF α-Mg (HCOO) : Which component is more sensitive to host-guest interaction?

Metal-organic frameworks (MOFs) are a class of important porous materials with many current and potential applications. Their applications almost always involve the interaction between host framework and guest species. Therefore, understanding of host-guest interaction in MOF systems is fundamentally important.

Solid-State O NMR Study of Carboxylic Acid Dimers: Simultaneously Accessing Spectral Properties of Low- and High-Energy Tautomers.

We report a solid-state O NMR study of several crystalline carboxylic acids. We found that, while each of these compounds forms discrete hydrogen-bonded dimers in the crystal lattice, their solid-state O magic-angle spinning (MAS) NMR spectra display quite different features and different temperature dependencies. We showed that experimentally observed O NMR spectral behaviors can be explained as being due to thermal averaging between the two tautomers that are produced as a result of concerted double-hydrogen hopping dynamics within each dimer.

Cleaving Carboxyls: Understanding Thermally Triggered Hierarchical Pores in the Metal-Organic Framework MIL-121.

Carboxylic acid linker ligands are known to form strong metal-carboxylate bonds to afford many different variations of permanently microporous metal-organic frameworks (MOFs). A controlled approach to decarboxylation of the ligands in carboxylate-based MOFs could result in structural modifications, offering scope to improve existing properties or to unlock entirely new properties. In this work, we demonstrate that the microporous MOF MIL-121 is transformed to a hierarchically porous MOF via thermally triggered decarboxylation of its linker.

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation.

Biomass pyrolysis by solid acid catalysts is one of many promising technologies for sustainable production of hydrocarbon liquid fuels and value-added chemicals, but these complex chemical transformations are still poorly understood. A series of well-defined model SiO -supported alumina catalysts were synthesized and molecularly characterized, under dehydrated conditions and during biomass pyrolysis, with the aim of establishing fundamental catalyst structure-activity/selectivity relationships. The nature and corresponding acidity of the supported AlO nanostructures on SiO were determined with Al/ H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations.

A Quadrupole-Central-Transition Co NMR Study of Cobalamins in Solution.

We report the first observation of quadrupole-central-transition (QCT) Co (I=7/2) NMR signals from three cobalamin (Cbl) compounds (CNCbl, MeCbl, and AdoCbl) dissolved in glycerol/water. Measurements were performed at four magnetic fields ranging from 11.7 to 21.

Loading across the Periodic Table: Introducing 14 Different Metal Ions To Enhance Metal-Organic Framework Performance.

Loading metal guests within metal-organic frameworks (MOFs) via secondary functional groups is a promising route for introducing or enhancing MOF performance in various applications. In this work, 14 metal ions (Li, Na, K, Mg, Ca, Ba, Zn, Co, Mn, Ag, Cd, La, In, and Pb) have been successfully introduced within the MIL-121 MOF using a cost-efficient route involving free carboxylic groups on the linker. The local and long-range structure of the metal-loaded MOFs is characterized using multinuclear solid-state NMR and X-ray diffraction methods.

Welcoming Gallium- and Indium-Fumarate MOFs to the Family: Synthesis, Comprehensive Characterization, Observation of Porous Hydrophobicity, and CO Dynamics.

The properties and applications of metal-organic frameworks (MOFs) are strongly dependent on the nature of the metals and linkers, along with the specific conditions employed during synthesis. Al-fumarate, trademarked as Basolite A520, is a porous MOF that incorporates aluminum centers along with fumarate linkers and is a promising material for applications involving adsorption of gases such as CO. In this work, the solvothermal synthesis and detailed characterization of the gallium- and indium-fumarate MOFs (Ga-fumarate, In-fumarate) are described.

Probing Calcium-Based Metal-Organic Frameworks via Natural Abundance Ca Solid-State NMR Spectroscopy.

Calcium-based metal-organic frameworks (MOFs) are of high importance due to their low cost and bio-compatible metal centers. Understanding the local environment of calcium in these materials is critical for unraveling the origins of specific MOF properties. Ca solid-state NMR spectroscopy is one of the very few techniques that can directly characterize calcium metal centers, however, the Ca nucleus is a very challenging target for solid-state NMR spectroscopy due to its extremely low natural abundance and resonant frequency.

Composition-Tunable Formamidinium Lead Mixed Halide Perovskites via Solvent-Free Mechanochemical Synthesis: Decoding the Pb Environments Using Solid-State NMR Spectroscopy.

Mixed-halide lead perovskites are becoming of paramount interest in the optoelectronic and photovoltaic research fields, offering band gap tunability, improved efficiency, and enhanced stability compared to their single halide counterparts. Formamidinium-based mixed halide perovskites (FA-MHPs) are critical to obtaining optimum solar cell performance. Here, we report a solvent-free mechanochemical synthesis (MCS) method to prepare FA-MHPs, starting with their parent compounds (FAPbX; X = Cl, Br, I), achieving compositions not previously accessible through the solvent synthesis (SS) technique.

A Quadrupole-Central-Transition O NMR Study of Nicotinamide: Experimental Evidence of Cross-Correlation between Second-Order Quadrupolar Interaction and Magnetic Shielding Anisotropy.

We have examined the O quadrupole-central-transition (QCT) NMR signal from [O]nicotinamide (vitamin B3) dissolved in glycerol. Measurements were performed at five magnetic fields ranging from 9.4 to 35.

Methylammonium Cation Dynamics in Methylammonium Lead Halide Perovskites: A Solid-State NMR Perspective.

In light of the intense recent interest in the methylammonium lead halides, CHNHPbX (X = Cl, Br, and I) as sensitizers for photovoltaic cells, the dynamics of the methylammonium (MA) cation in these perovskite salts has been reinvestigated as a function of temperature via H, N, and Pb NMR spectroscopy. In the cubic phase of all three salts, the MA cation undergoes pseudoisotropic tumbling (picosecond time scale). For example, the correlation time, τ, for the C-N axis of the iodide salt is 0.

Tracking the evolution and differences between guest-induced phases of Ga-MIL-53 via ultra-wideline Ga solid-state NMR spectroscopy.

Ga-MIL-53 is a metal-organic framework (MOF) that exhibits a "breathing effect," in which the pore size and overall MOF topology can be influenced by temperature, pressure, and host-guest interactions. The phase control afforded by this flexible framework renders Ga-MIL-53 a promising material for guest storage and sensing applications. In this work, the structure and behavior of four Ga-MIL-53 phases (as, ht, enp and lt), along with CO adsorbed within Ga-MIL-53 at various loading levels, has been investigated using Ga solid-state NMR (SSNMR) experiments at 21.