Understanding water reaction pathways to control the hydrolytic reactivity of a Zn metal-organic framework.

Metal-organic frameworks (MOFs) are a class of porous materials that are of topical interest for their utility in water-related applications. Nevertheless, molecular-level insight into water-MOF interactions and MOF hydrolytic reactivity remains understudied. Herein, we report two hydrolytic pathways leading to either structural stability or framework decomposition of a MOF (ZnMOF-1).

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.

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.

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.

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.

Higher Magnetic Fields, Finer MOF Structural Information: O Solid-State NMR at 35.2 T.

The spectroscopic study of oxygen, a vital element in materials, physical, and life sciences, is of tremendous fundamental and practical importance. O solid-state NMR (SSNMR) spectroscopy has evolved into an ideal site-specific characterization tool, furnishing valuable information on the local geometric and bonding environments about chemically distinct and, in some favorable cases, crystallographically inequivalent oxygen sites. However, O is a challenging nucleus to study via SSNMR, as it suffers from low sensitivity and resolution, owing to the quadrupolar interaction and low O natural abundance.

Anhydride Post-Synthetic Modification in a Hierarchical Metal-Organic Framework.

Metal-organic frameworks (MOFs) are important porous materials. Post-synthetic modification (PSM) of MOFs via the pendant groups or secondary functional groups of organic linkers has been widely used to introduce new or enhance existing properties of MOFs for various practical applications. In this work, we have constructed, for the first time, a novel platform for PSM of MOFs by introducing an anhydride functional group into a hierarchically porous MOF (MIL-121) as an effective anchor.

Exploring Host-Guest Interactions in the α-Zn(HCOO) Metal-Organic Framework.

Metal-organic frameworks (MOFs) are promising gas adsorbents. Knowledge of the behavior of gas molecules adsorbed inside MOFs is crucial for advancing MOFs as gas capture materials. However, their behavior is not always well understood.

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.

CO Guest Interactions in SDB-Based Metal-Organic Frameworks: A Solid-State Nuclear Magnetic Resonance Investigation.

Metal-organic frameworks (MOFs) are promising materials for greener carbon monoxide (CO) capture and separation processes. SDB-based (SDB = 4,4-sulfonyldibenzoate) MOFs are particularly attractive due to their remarkable gas adsorption capacity under humid conditions. However, to the best of our knowledge, their CO adsorption abilities have yet to be investigated.

Solid-State NMR Spectroscopy: A Powerful Technique to Directly Study Small Gas Molecules Adsorbed in Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) have shown great potential in gas separation and storage, and the design of MOFs for these purposes is an on-going field of research. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy is a valuable technique for characterizing these functional materials. It can provide a wide range of structural and motional insights that are complementary to and/or difficult to access with alternative methods.

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.

Characterization of Metal-Organic Frameworks: Unlocking the Potential of Solid-State NMR.

An exciting advance in materials science is the discovery of hybrid organic-inorganic solids known as metal-organic frameworks (MOFs). Although they have numerous important applications, the local structures, specific molecular-level features, and guest behaviors underpinning desirable properties and applications are often unknown. Solid-state nuclear magnetic resonance (SSNMR) is a powerful tool for MOF characterization as it provides information complementary to that from X-ray diffraction (XRD).

Crystalline Superlattices of Nanoscopic CdS Molecular Clusters: An X-ray Crystallography and Cd SSNMR Spectroscopy Study.

Systematic Cd solid-state (SS) NMR experiments were performed to correlate X-ray crystallographic data with SSNMR parameters for a set of CdS-based materials, varying from molecular crystals of small complexes [Cd(SPh)] and [Cd(SPh)] to superlattices of large monodisperse clusters [CdS(SPh)(dmf)] and 1.9 nm CdS. Methodical data analysis allowed for assigning individual resonances or resonance groups to particular types of cadmium sites residing in different chemical and/or crystallographic environments.

Binary Complementary Filters for Compressive Raman Spectroscopy.

The previously described optimized binary compressive detection (OB-CD) strategy enables fast hyperspectral Raman (and fluorescence) spectroscopic analysis of systems containing two or more chemical components. However, each OB-CD filter collects only a fraction of the scattered photons and the remainder of the photons are lost. Here, we present a refinement of OB-CD, the OB-CD2 strategy, in which all of the collected Raman photons are detected using a pair of complementary binary optical filters that direct photons of different colors to two photon counting detectors.

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.

Sizable dynamics in small pores: CO location and motion in the α-Mg formate metal-organic framework.

Metal-organic frameworks (MOFs) are promising materials for carbon dioxide (CO) adsorption and storage; however, many details regarding CO dynamics and specific adsorption site locations within MOFs remain unknown, restricting the practical uses of MOFs for CO capture. The intriguing α-magnesium formate (α-Mg(HCOO)) MOF can adsorb CO and features a small pore size. Using an intertwined approach of C solid-state NMR (SSNMR) spectroscopy, H-C cross-polarization SSNMR, and computational molecular dynamics (MD) simulations, new physical insights and a rich variety of information have been uncovered regarding CO adsorption in this MOF, including the surprising suggestion that CO motion is restricted at elevated temperatures.

Grasping hydrogen adsorption and dynamics in metal-organic frameworks using (2)H solid-state NMR.

Record greenhouse gas emissions have spurred the search for clean energy sources such as hydrogen (H2) fuel cells. Metal-organic frameworks (MOFs) are promising H2 adsorption and storage media, but knowledge of H2 dynamics and adsorption strengths in these materials is lacking. Variable-temperature (VT) (2)H solid-state NMR (SSNMR) experiments targeting (2)H2 gas (i.

Deducing CO2 motion, adsorption locations and binding strengths in a flexible metal-organic framework without open metal sites.

Microporous metal-organic frameworks (MOFs) have high surface areas and porosities, and are well-suited for CO2 capture. MIL-53 features corner-sharing MO4(OH)2 (M = Al, Ga, Cr, etc.) octahedra interconnected by benzenedicarboxylate linkers that form one-dimensional rhombic tunnels, and exhibits an excellent adsorption ability for guest molecules such as CO2.

Monitoring and understanding the paraelectric-ferroelectric phase transition in the metal-organic framework [NH4 ][M(HCOO)3 ] by solid-state NMR spectroscopy.

The paraelectric-ferroelectric phase transition in two isostructural metal-organic frameworks (MOFs) [NH4 ][M(HCOO)3 ] (M=Mg, Zn) was investigated by in situ variable-temperature (25) Mg, (67) Zn, (14) N, and (13) C solid-state NMR (SSNMR) spectroscopy. With decreasing temperature, a disorder-order transition of NH4 (+) cations causes a change in dielectric properties. It is thought that [NH4 ][Mg(HCOO)3 ] exhibits a higher transition temperature than [NH4 ][Zn(HCOO)3 ] due to stronger hydrogen-bonding interactions between NH4 (+) ions and framework oxygen atoms.

Fluorescence modeling for optimized-binary compressive detection Raman spectroscopy.

The recently-developed optimized binary compressive detection (OB-CD) strategy has been shown to be capable of using Raman spectral signatures to rapidly classify and quantify liquid samples and to image solid samples. Here we demonstrate that OB-CD can also be used to quantitatively separate Raman and fluorescence features, and thus facilitate Raman-based chemical analyses in the presence of fluorescence background. More specifically, we describe a general strategy for fitting and suppressing fluorescence background using OB-CD filters trained on third-degree Bernstein polynomials.

Wobbling and Hopping: Studying Dynamics of CO2 Adsorbed in Metal-Organic Frameworks via (17)O Solid-State NMR.

Knowledge of adsorbed gas dynamics within microporous solids is crucial for the design of more efficient gas capture materials. We demonstrate that (17)O solid-state NMR (SSNMR) experiments allow one to obtain accurate information on CO2 dynamics within metal-organic frameworks (MOFs), using CPO-27-M (M = Mg, Zn) as examples. Variable-temperature (VT) (17)O SSNMR spectra acquired from 150 to 403 K yield key parameters defining the CO2 motions.