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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. Characterization of MOF defects is important, but very challenging due to the local nature and short-range ordering. In this work, we have introduced the ordered vacancies (the defects) in the form of the coordinatively unsaturated sites (CUSs) into the framework of MOF MIL-120(Al). The creation of ordered vacancies is achieved by replacing one quarter of the BTEC (1,2,4,5-benzenetetracarboxylate) with BDC (benzene-1,4-dicarboxylate) linkers. Both parent and defective MOFs were characterized by multinuclear solid-state NMR spectroscopy. ¹H MAS NMR is used to characterize the hydrogen bonding in these MOFs, whereas ¹³C CP MAS NMR confirms unambiguously that the BDC is incorporated into the framework. One-dimensional ²⁷Al MAS NMR provides direct evidence of the coordinatively unsaturated Al sites (the defects). Furthermore, ²⁷Al 3QMAS experiments at 21.1 ​T allow direct identification of one penta-coordinated and three chemically inequivalent octahedral Al sites in the defective MIL-120(Al). Two of the above-mentioned octahedral Al sites are in the domain which appears defect-free. The third octahedral Al site is near the defective site. This work clearly demonstrates the power of solid-state NMR spectroscopy for characterization of defective MOFs.

Combining a cryogenic MAS probe and high magnetic field results in remarkable signal enhancement, permitting MOF characterization by 67Zn 3QMAS NMR at natural abundance.

The revival of ternary halides Li-M-X (M = Y, In, Zr, etc.; X = F, Cl, Br) as solid-state electrolytes (SSEs) shows promise in realizing practical solid-state batteries due to their direct compatibility toward high-voltage cathodes and favorable room-temperature ionic conductivities. Most of the reported superionic halide SSEs have a structural pattern of [MCl

Crystallization of DNL-6, a silicoaluminophosphate (SAPO) based molecular sieve with the RHO topology, was investigated under both the hydrothermal synthesis (HTS) and dry-gel conversion (DGC) conditions. Crystallization of DNL-6 under the HTS conditions is rather fast. But a combination of crystallization under the DGC conditions and reducing reaction temperature slow down the reactions, allowing for intermediates to be captured. Under the DGC conditions, DNL-6 crystallizes through a semi-crystalline layered phase. The nature of this intermediate is aluminophosphate (AlPO) rather than SAPO with most P atoms having a local environment of P(–O–Al)3(OH). The surfactant (cetyltrimethylammonium chloride) used for synthesis appears to be part of the layered intermediate. Si is directly incorporated in the DNL-6 framework via SM II mechanism when the semi-crystalline AlPO phase is transforming to DNL-6 with the assistance of a very small amount of water. Both the structure directing agent and the surfactant play a role in the formation of DNL-6, as they were found within the final synthesized products. SEM data show that hydrothermal synthesis produces a much more crystalline product. The facts that the semi-crystalline layered phase was also observed in the powder X-ray diffraction patterns of the solid samples obtained under the HTS conditions and that the evolution of the local structure around P and Al in the intermediate phases are similar imply that under the reaction conditions employed in the present study, the formation pathways of DNL-6 under the HTS and DGC conditions appear to have some similarities.

Summary The trade-off between selectivity and adsorption capacity with porous materials is a major roadblock to reducing the energy footprint of gas separation technologies. To address this matter, we report herein a systematic crystal engineering study of C2H2 removal from CO2 in a family of hybrid ultramicroporous materials (HUMs). The HUMs are composed of the same organic linker ligand, 4-(3,5-dimethyl-1H-pyrazol-4-yl)pyridine, pypz, three inorganic pillar ligands, and two metal cations, thereby affording six isostructural pcu topology HUMs. All six HUMs exhibited strong binding sites for C2H2 and weaker affinity for CO2. The tuning of pore size and chemistry enabled by crystal engineering resulted in benchmark C2H2/CO2 separation performance. Fixed-bed dynamic column breakthrough experiments for an equimolar (v/v = 1:1) C2H2/CO2 binary gas mixture revealed that one sorbent, SIFSIX-21-Ni, was the first C2H2 selective sorbent that combines exceptional separation selectivity (27.7) with high adsorption capacity (4 mmol·g−1)., Graphical abstract, Highlights • Six isostructural hybrid ultramicroporous materials are prepared and characterized • Crystal engineering approach enabled fine-tuning of pore size and chemistry • Weak CO2/strong C2H2 affinity resulted in high C2H2/CO2 separation selectivities • SIFSIX-21-Ni: benchmark selectivity/uptake capacity for C2H2/CO2 separation, The bigger picture It is generally recognized that porous solids (sorbents) with high selectivity and high adsorption capacity offer potential for energy-efficient gas separations. Unfortunately, there is generally a trade-off between capacity and selectivity, which represents a roadblock to the utility of sorbents in key industrial processes. For example, acetylene (C2H2), an important fuel and chemical intermediate, is produced with CO2 as an impurity, and the similar physicochemical properties of C2H2 and CO2 mean that most sorbents are poorly selective. Hybrid ultramicroporous materials (HUMs) are candidates for gas separations as they exhibit benchmark selectivity for several key gas pairs. Unfortunately, existing HUMs are handicapped by low capacity. We report a new HUM, SIFSIX-21-Ni, that addresses the trade-off between selectivity and capacity that has plagued sorbents, as its high uptake and high selectivity renders it the new benchmark for C2H2/CO2 separation performance., A new family of six isostructural hybrid ultramicroporous materials that enabled high adsorption capacity as well as high experimental separation selectivity values for C2H2/CO2 separation.

MIL-53(Al) is a member of the most extensively studied metal-organic framework (MOF) families owing to its "flexible" framework and superior stability. 17 O solid-state NMR (SSNMR) spectroscopy is an ideal site-specific characterization tool as it probes local oxygen environments. Because oxygen local structure is often altered during phase change, 17 O SSNMR can be used to follow phase transitions. However, 17 O is a challenging nucleus to study via SSNMR due to its low sensitivity and resolution arising from the very low natural abundance of 17 O isotope and its quadrupolar nature. In this work, we describe that by using 17 O isotopic enrichment and performing 17 O SSNMR experiments at an ultrahigh magnetic field of 35.2 T, all chemically and crystallographically inequivalent oxygen sites in two representative MIL-53(Al) (as-made and water adsorbed) phases can be completely resolved. The number of signals in each phase is consistent with that predicted from the space group refined from powder X-ray diffraction data. The 17 O 1D magic-angle spinning (MAS) and 2D triple-quantum MAS (3QMAS) spectra at 35.2 T furnish fine information about the host-guest interactions and the structural changes associated with phase transition. The ability to completely resolve multiple chemically and crystallographically inequivalent oxygen sites in MOFs at very high magnetic field, as illustrated in this work, significantly enhances the potential for using the NMR crystallography approach to determine crystal structures of new MOFs and verify the structures of existing MOFs obtained from refining powder X-ray diffraction data.

International audience; The spectroscopic study of oxygen, a vital element in materials, physical, and life sciences, is of tremendous fundamental and practical importance. 17O 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, 17O is a challenging nucleus to study via SSNMR, as it suffers from low sensitivity and resolution, owing to the quadrupolar interaction and low 17O natural abundance. Herein, we report a significant advance in 17O SSNMR spectroscopy. 17O isotopic enrichment and the use of an ultrahigh 35.2 T magnetic field have unlocked the identification of many inequivalent carboxylate oxygen sites in the as-made and activated phases of the metal–organic framework (MOF) α-Mg3(HCOO)6. The subtle 17O spectral differences between the as-made and activated phases yield detailed information about host–guest interactions, including insight into nonconventional O···H–C hydrogen bonding. Such weak interactions often play key roles in the applications of MOFs, such as gas adsorption and biomedicine, and are usually difficult to study via other characterization routes. The power of performing 17O SSNMR experiments at an ultrahigh magnetic field of 35.2 T for MOF characterization is further demonstrated by examining activation of the MIL-53(Al) MOF. The sensitivity and resolution enhanced at 35.2 T allows partially and fully activated MIL-53(Al) to be unambiguously distinguished and also permits several oxygen environments in the partially activated phase to be tentatively identified. This demonstration of the very high resolution of 17O SSNMR recorded at the highest magnetic field accessible to chemists to date illustrates how a broad variety of scientists can now study oxygen-containing materials and obtain previously inaccessible fine structural information.

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 0.3-0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal-organic framework Ca-trimesate, Ca(HBTC)⋅H2 O (H3 BTC=trimesic acid), bnn-1-Ca-H2 O, affords a narrow pore variant, Ca(HBTC), bnn-1-Ca. Whereas bnn-1-Ca-H2 O (pore diameter 0.34 nm) exhibits ultra-high CO2 /N2 , CO2 /CH4 , and C2 H2 /C2 H4 binary selectivity, bnn-1-Ca (pore diameter 0.31 nm) offers ideal selectivity for H2 /CO2 and H2 /N2 under cryogenic conditions. Ca-trimesate, the first physisorbent to exhibit H2 sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.

Using in situ generated H2O2 is potentially an effective approach for benzyl alcohol selective oxidation. While the microporous titanium silicate (TS-1) supported with Pd is promising for selective oxidation, the Pd particles are preferentially anchored on the external surface, which leads to the problems such as non-uniform dispersion and low thermal stability. Here, we prepared a Pd@HTS-1 catalyst in which the Pd subnanoparticles were encapsulated in the channels of the hierarchical TS-1 (HTS-1), for benzyl alcohol selective oxidation with in situ produced H2O2. We find that the oxidation rate of benzyl alcohol by in situ H2O2 over the Pd@HTS-1 is up to 4268.8 mmol h-1 kgcat -1, and the selectivity of benzaldehyde approaches 100%. In contrast to the conventional Pd/HTS-1, the present Pd@HTS-1 benefits the benzyl alcohol selective oxidation due to the increased dispersion of Pd particles (forming uniformly dispersed subnano-sized particles), as well as the confinement effect and hierarchical porosity of the HTS-1 host. We further suggested that hydrogen peroxide produced in situ from the molecular hydrogen and oxygen over the Pd sites can be spilled over to the framework Ti4+ sites, forming the Ti-OOH active species, which selectively oxidizes the chemisorbed benzyl alcohol to benzaldehyde on the Pd sites.

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. We have demonstrated that the combination of the high reactivity of anhydride and hierarchical porosity makes this protocol particularly novel and important, as it led to excellent opportunities of incorporating not only a wide variety of organic molecules with different sizes and chemical nature but also the noble metal complexes in MOFs. Specifically, we show that the anhydride group decorated in the MOF exhibits a high reactivity toward covalently binding 10 different guest molecules including alcohols, amines, thiols, and noble metal (Pt(II)/Pt(IV)) complexes, whereas the hierarchical pores created in the MOF allow the incorporation of guest species varying in size from methanol to larger molecules such as polyaromatic amines. This novel approach provides the community with a new avenue to prepare MOF-based materials for targeted applications. To illustrate this point, we furnish an example of using this new platform to prepare a Pt-based electrocatalyst which shows excellent catalytic activity toward the oxygen reduction reaction (ORR), a pivotal half-reaction in hydrogen-oxygen fuel cells and other energy storage and conversion devices.

Sulfide solid electrolytes have recently attracted significant interest for use in all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity. However, one of the main challeng...

Crystallization of zeolite ZSM-39 (MTN), a clathrate and silicate analogue of the 17 Å cubic gas hydrate, was examined in a solvent system involving a tetramethylammonium chloride – 1,6-hexanediol deep eutectic mixture and significant amount of water. The crystallization process was followed by powder X-ray diffraction (PXRD), and solid-state nuclear magnetic resonance (SSNMR) techniques involving several nuclei such as 19F, 29Si, and 13C. The results indicate that the crystallization starts from the arrangement of amorphous Si–O–Si species around the tetramethylammonium ions and subsequent formation of the cages in the precursors similar to [51264] cages in the MTN topology. The larger [51264] cages are then connected via the smaller [512] cages containing the fluoride ions to form the final MTN structure. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses show that the crystal growth rates along and directions are roughly the same, suggesting that the (100) and (111) planes have similar stability under the crystallization conditions used. AFM study also shows that the freshly born nuclei on the (100) face are of a height of 2 nm, suggesting a layer by layer growth of the polyhedral crystal.

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 ...

The selective synthesis of the zinc-acetato-phosphinidene cluster [Zn6(μ3-PSiMe3)4(OAc)4(NC5H5)5] 1 is presented. The cluster serves as a stable, single-source precursor to yield soluble zinc phosphide nanoparticles via P–Si bond activation and AcOSiMe3 elimination when heated in oleylamine or other donor solvents.

PbSDB and CdSDB (SDB=4,4'-sulfonyldibenzoate) are two structurally related SDB-based metal-organic frameworks (MOFs) that demonstrate promising potential for selective CO2 adsorption capabilities. The structural stabilities and guest-host interactions between CO2 and PbSDB or CdSDB frameworks at high pressures up to 13 GPa in situ were comparatively investigated by Raman spectroscopy, FTIR spectroscopy, and synchrotron X-ray diffraction. Although both empty frameworks exhibited high chemical stabilities upon compression, they show different pressure-induced modifications in crystallinity. This difference can be attributed to their different coordination topologies that result in near isotropic contraction of unit cells for the CdSDB framework but anisotropic for the PbSDB framework. Furthermore, the CO2 -loaded PbSDB and CdSDB frameworks at high pressures show strongly contrasting guest-host interactions in terms of the pressure-regulated CO2 adsorption sites. In both frameworks, pressure can highly efficiently promote the formation of new CO2 adsorption sites and the enhancement of guest-host interactions. In the CO2 -loaded PbSDB framework, in particular, the peculiar pressure-tuned CO2 population was observed preferentially on one of the two adsorption sites in response to external compression. These unique guest-host interaction behaviors can also be unambiguously correlated to their different topological origins. These findings for the PbSDB and CdSDB frameworks provide in-depth understanding of the structure-property relationship, which is of fundamental importance for CO2 storage application in SDB-based MOFs.

It holds great promise to develop thrombolytic agent delivery systems with prolonged circulation time, minimized adverse effect, and preferential thrombolytic activity at the thrombus site. In this work, a pH-triggered delivery system for the thrombolytic agent was synthesized. Fluorescein isothiocyanate-labeled urokinase-type plasminogen activator (uPA) was conjugated to oxidized dextran (Oxd) via the pH-sensitive imine linkage, and then the conjugation was modified with RGD peptide. The uPA-Oxd conjugates displayed enhanced stability to resist enzymatic hydrolysis in comparison with the native uPA. Meanwhile, the bioactivity of uPA in the uPA-Oxd conjugates was masked at physiological pH and regenerated under weak acidic condition due to the release of uPA via the hydrolysis of imine bond in the conjugates. RGD modification endowed the conjugates with targeting ability to the thrombus site due to the specific peptide-GP IIb/IIIa binding and enhanced the thrombolysis efficacy via an endogenous low-pH triggered uPA release at the thrombus site, reducing the risk of acute hemorrhage complication. Thus, the RGD modified pH-sensitive uPA-Oxd conjugates provide a promising potential of the system in local thrombolysis therapy.

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 NMR spectroscopy is an excellent technique for investigating host-guest interaction as it provides information complementary to that obtained from X-ray diffraction. In this work, using MOF α-Mg3 (HCOO)6 as an example, we demonstrated that 13 C chemical shift tensor of organic linker can be utilized to probe the host-guest interaction in MOFs. Obtaining 13 C chemical shift tensor components (δ11 , δ22 , and δ33 , where δ11 ≥ δ22 ≥ δ33 ) in this MOF is particularly challenging as there are six coordinatively equivalent but crystallographically non-equivalent carbons in the unit cell with very similar local coordination environment. Two-dimensional magic-angle-turning experiments were employed to measure the 13 C chemical shift tensors of each individual crystallographically non-equivalent carbon in three microporous α-Mg3 (HCOO)6 samples with different guest species. The results indicate that the δ22 component (with its direction approximately being co-planar with the formate anion and perpendicular to the C-H bond) is more sensitive to the adsorbate molecules inside the MOF channel due to the weak C-H···O hydrogen bonding or the ring current effect of benzene. The 13 C isotropic chemical shift, on the other hand, seems much less sensitive to the subtle changes in the local environment around formate linker induced by adsorption. The approach described in this study may be used in future studies on host-guest interaction within MOFs.

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. 43 Ca solid-state NMR spectroscopy is one of the very few techniques that can directly characterize calcium metal centers, however, the 43 Ca nucleus is a very challenging target for solid-state NMR spectroscopy due to its extremely low natural abundance and resonant frequency. In this work, natural abundance 43 Ca solid-state NMR spectroscopy, at a high magnetic field of 21.1 T, has been employed to characterize several calcium-based MOFs. We demonstrate that 43 Ca NMR spectra and quantum chemical calculations can probe the local structure of calcium metal centers within MOFs, investigate the presence of guests, and monitor phase changes.

ConspectusAn 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). We describe our novel pursuits in the three primary applications of SSNMR for MOF characterization: interrogating the metal center, targeting linker molecules, and probing guests.MOFs have relatively low densities, and the incorporated metals are often quadrupolar nuclei, making SSNMR detection difficult. Recently, we examined the local structures of metal centers (i.e., 25Mg, 47/49Ti, 63/65Cu, 67Zn, 69/71Ga, 91Zr, 115In, 135/137Ba, 139La, 27Al) in representative MOFs by SSNMR at a high magnetic field...

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 2 adsorbed within Ga-MIL-53 at various loading levels, has been investigated using 69/71 Ga solid-state NMR (SSNMR) experiments at 21.1 T and 9.4 T. 69/71 Ga SSNMR spectra are observed to be very sensitive to distortions in the octahedral GaO 6 secondary building units within Ga-MIL-53; by extension, Ga NMR parameters are indicative of the particular crystallographic phase of Ga-MIL-53. The evolution of Ga NMR parameters with CO 2 loading levels in Ga-MIL-53 reveals that the specific CO 2 loading level offers a profound degree of control over the MOF phase, and the data also suggests that a re-entrant phase transition is present. Adsorption of various organic compounds within Ga-MIL-53 has been investigated using a combination of thermal gravimetric analysis (TGA), powder X-ray diffraction (pXRD) and 69/71 Ga SSNMR experiments. Notably, pXRD experiments reveal that guest adsorption and host-guest interactions trigger unambiguous changes in the long-range structure of Ga-MIL-53, while 69/71 Ga SSNMR parameters yield valuable information regarding the effect of the organic adsorbates on the local GaO 6 environments. This approach shows promise for the ultra-wideline investigation of other quadrupolar metal nuclei in MIL-53 ( e.g. , In-MIL-53) and MOFs in general, particularly in regards to adsorption-related applications.

Myeloid-derived growth factor (MYDGF) is a paracrine-acting protein that is produced by bone marrow-derived monocytes and macrophages to protect and repair the heart after myocardial infarction (MI). This effect can be used for the development of protein-based therapies for ischemic tissue repair, also beyond the sole application in heart tissue. Here, we report the X-ray structure of MYDGF and identify its functionally relevant receptor binding epitope. MYDGF consists of a 10-stranded β-sandwich with a folding topology showing no similarities to other cytokines or growth factors. By characterizing the epitope of a neutralizing antibody and utilizing functional assays to study the activity of surface patch-mutations, we were able to localize the receptor interaction interface to a region around two surface tyrosine residues 71 and 73 and an adjacent prominent loop structure of residues 97–101. These findings enable structure-guided protein engineering to develop modified MYDGF variants with potentially improved properties for clinical use., Myeloid-derived growth factor (MYDGF) is an angiogenic growth factor with therapeutic potential for ischemic tissue repair and the receptor is still unknown. Here the authors present the crystal structure of human MYDGF and identify its functional epitope through mutagenesis studies.

Metal–organic frameworks (MOFs) have shown great promise for the adsorption and separation of gases, including the greenhouse gas CO2. In order to improve performance and realize practical applications for MOFs as CO2 adsorbents, a deeper understanding of the number and type of CO2 adsorption mechanisms must be unlocked, along with fine details of CO2 motion within MOFs. Using several complementary characterization methods is a promising protocol for comprehensively investigating the various host–guest interactions between MOFs and CO2. In this work, a combination of solid state NMR (SSNMR) and single crystal X-ray diffraction (SCXRD) has been utilized to reveal both the location and dynamics of adsorbed CO2 within the related PbSDB and CdSDB MOFs, as well as to probe the role of metal centers in CO2 adsorption. 13C SSNMR experiments targeting CO2 reveal the number of unique adsorption sites and the types of CO2 dynamics present, as well as their associated motional rates and angles. 111Cd and 207Pb SSNMR...

This paper presents the first example of high-silica and siliceous zeolite synthesis in the urea/choline chloride mixture as a deep eutectic solvent (DES) using F– as the mineralizing agent. A urea/choline chloride mixture was previously used as solvent to prepare AlPO4-based microporous materials SIZ-2 and AlPO-CJ2. However, generating these materials depends on the formation of ammonium ion as a structure-directing agent (SDA) that is the side product of urea decomposition. In the present study, we show that several highly siliceous zeolites with targeted topologies (MFI, BEA, MEL, and MTN) can be purposely synthesized by adding SDAs of choice rather than relying on solvent decomposition. The Si atoms in zeolite Beta synthesized in a urea/choline chloride mixture exhibit exceptionally high local ordering as shown in a 29Si MAS NMR spectrum. The synthesis of ZSM-11 using eutectic solvents or ionic liquid has not been reported. The major challenge in ZSM-11 synthesis is the intergrown structure formed with ZSM-5 due to the high similarity in their topologies. The present work shows that preparation of pure ZSM-11 can be achieved in urea/choline chloride DES using either DPHMII or DECDMPI as SDA. Using a urea/choline chloride mixture rather than alcohol-based traditional nonaqueous solvents is the key for the success of preparing phase-pure ZSM-11 free of any MFI intergrowths. This is because some alcohols can serve as SDA for MFI. The use of urea/choline chloride based DES eliminates the potential templateing effect of solvent for MFI formation. For MTN zeolite, morphology may be controlled in urea/choline chloride by choosing different SDAs. The disadvantage of this system is the long reaction times.

The unique structural topology of metal-organic framework (MOF) MIL-68, featuring two types of channels with distinct pore sizes, makes it a promising candidate for application in gas storage and separation. In this study, the behavior of as-made and activated MIL-68(In) was investigated in a diamond-anvil cell under high pressure by in situ IR spectroscopy. The framework exhibits high stability under compression up to 9 GPa, whereas the bridging OH groups appear to be very sensitive to compression. Pressure-induced structural modifications were found to be completely reversible for as-made MIL-68(In) but irreversible for the activated framework. Moreover, the addition of Nujol as pressure-transmitting medium makes the framework more resilient to pressure. Finally, when loaded with CO2, the framework exhibited interesting differential binding affinities with CO2 in the hexagonal and triangular pores at different pressures. The pressure-enhanced CO2 storage behavior and the guest-host interaction mechanism between CO2 and the MOF framework were explored with the aid of Monte Carlo simulations. These studies demonstrated great potential for MIL-68(In) in gas-storage applications that require extreme loading pressures.

Crystalline FeAlO3/FeAl2O4 nanonets were synthesized by a modified template-assisted approach using anodic aluminum oxide (AAO) as a reactive and sacrificial template to direct and promote interfacial reaction growth (IRG). The as-prepared nanonets replicate the morphology of the porous AAO template and contain mixed FeAlO3 and FeAl2O4. To extend the applicability of the sacrificial-template-assisted IRG approach, porous anodic titanium oxide (ATO) was used as template in place of AAO, giving rise to Zn2TiO4 nanonet/nanotube and PbTiO3 nanonet/nanotube. These latter products are polycrystalline due to the polycrystalline nature of the ATO template. Growth mechanism for the formation of the Zn2TiO4 and PbTiO3 nanostructures is proposed. The present study shows that the IRG approach can be extended to fabricate patterned complex oxide nanomaterials that may find applications in a wide range of nanotechnologies such as electronics, photonics and spintronics.

Metal-organic frameworks (MOFs) are versatile materials that incorporate metal centers along with organic linkers in highly ordered, intricate structures. MIL-53 is a MOF that exhibits a “breathing effect,” where the pore size and MOF topology are profoundly influenced by the identity and binding mechanism of guest molecules. This phenomenon renders MIL-53 a promising candidate for sensing applications. In this report, the adsorption of various organic compounds within MIL-53 is investigated using a combination of complementary techniques. Thermal gravimetric analysis experiments confirm loading of the guest molecules and yield insight into adsorption interactions and strengths. Significant guest-induced changes in the crystal structure of MIL-53 are revealed by powder X-ray diffraction experiments; specific unique phases of MIL-53 are related to the identity of the guest molecule and its binding mechanism to the framework. 27Al and 13C solid-state NMR experiments probe the interaction between guest molecules and MIL-53. The relationship between the nature of the guest, the structure of MIL-53, and 27Al NMR parameters is explored. 27Al NMR parameters are sensitive to the host-guest binding mechanism (i.e., hydrogen-bonding or π–π stacking interactions) and yield valuable information regarding the influence of the adsorbates on the local aluminum environment. This combination of physical characterization techniques is a useful probe of guest adsorption and the breathing effect within MIL-53 and should prove useful for investigation of related MOFs.

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. In this Concept article, the recent advances made in SSNMR investigations of small gas molecules (i.e., carbon dioxide, carbon monoxide, hydrogen gas and light hydrocarbons) adsorbed in MOFs are discussed. These studies demonstrate the breadth of information that can be obtained by SSNMR spectroscopy, such as the number and location of guest adsorption sites, host-guest binding strengths and guest mobility. The knowledge acquired from these experiments yields a powerful tool for progress in MOF development.

Phytosterols are well-known for their cholesterol-lowering effects, and the structures and forms of phytosterols affect their bioactivity. We aimed to illustrate the phytosterol profiles in common foods and estimate their natural intake in five geographical regions and among different age groups in China. In total, 12 phytosterols in free and esterified forms of 119 foods from five regions across China were examined using gas chromatography-mass spectrometry. Then, the dietary intake of phytosterols was calculated combined with the dietary foods intake data of Chinese people. The total phytosterol content was highest in vegetable oils (150.4-1230.9 mg/100 g), followed by legumes (129.6-275.6 mg/100 g), nuts (18.9-255.2 mg/100 g), and cereals (11.9-93.8 mg/100 g). Vegetables and fruits contained lower contents of total phytosterols. Phytosterols were mainly esterified in most common foods except in nuts. The predominant phytosterols were β-sitosterol, campesterol, and stigmasterol, all of which belonged to plant sterols and 4-desmethylsterols. Total phytosterol intake varied across different regions, ranging between 257.7 and 473.7 mg/standard-person (sp)/day, with the highest intake in Beijing, followed by Hangzhou, Wuhan, Chongqing, and Guangzhou. However, phytosterol proportion was similar across regions, with β-sitosterol accounting for 46.5-50.3% of the natural intake. Phytosterol intake was mainly constituted by plant sterols and 4-desmethylsterols in esterified form (61.9-74.6%). At the age of 2-70 years, phytosterol intake ranged from 154.3 mg/day to 348.0 mg/day in the national scale.

Methane is a promising clean and inexpensive energy alternative to traditional fossil fuels, however, its low volumetric energy density at ambient conditions has made devising viable, efficient methane storage systems very challenging. Metal-organic frameworks (MOFs) are promising candidates for methane storage. In order to improve the methane storage capacity of MOFs, a better understanding of the methane adsorption, mobility, and host-guest interactions within MOFs must be realized. In this study, methane adsorption within α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , SIFSIX-3-Zn, and M-MOF-74 (M=Mg, Zn, Ni, Co) has been comprehensively examined. Single-crystal X-ray diffraction (SCXRD) experiments and DFT calculations of the methane adsorption locations were performed for α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , and SIFSIX-3-Zn. The SCXRD thermal ellipsoids indicate that methane possesses significant mobility at the adsorption sites in each system. 2 H solid-state NMR (SSNMR) experiments targeting deuterated CH3 D guests in α-Mg3 (HCO2 )6 , α-Zn3 (HCO2 )6 , SIFSIX-3-Zn, and MOF-74 yield an interesting finding: the 2 H SSNMR spectra of methane adsorbed in these MOFs are significantly influenced by the chemical shielding anisotropy in addition to the quadrupolar interaction. The chemical shielding anisotropy contribution is likely due mainly to the nuclear independent chemical shift effect on the MOF surfaces. In addition, the 2 H SSNMR results and DFT calculations strongly indicate that the methane adsorption strength is linked to the MOF pore size and that dispersive forces are responsible for the methane adsorption in these systems. This work lays a very promising foundation for future studies of methane adsorption locations and dynamics within adsorbent MOF materials.

Micrometer-sized superparticles, self-assembled from metallic or semiconducting nanoclusters, can be used as convenient building blocks for preparing functional materials, utilizing the electronic and optical properties resulting from the quantum confinement as well as from the coupling between nanoscopic constituents. Herein, we describe a facile route to prepare crystalline, cubic superparticles of monodisperse nanoclusters of CdS 1.9 nm in size by means of the thermally induced conversion of the readily prepared cadmium thiophenolate complex (Me4N)2[Cd(SPh)4]. Furthermore, we illustrate the effects that additional quaternary ammonium salts can have on the size and dispersity of the nanoclusters formed and on the nature of their self-assembly into secondary structures, with the preparation and characterization of spherical superparticles of CdS, composed of individual nanoclusters 2.3 nm in size. Details on the formation, structural characterization (via powder and single crystal X-ray diffraction, HRTE...

Metal–organic frameworks (MOFs) are important materials with many actual and potential applications. Crystal structure of many MOFs is determined by single-crystal X-ray diffraction. However, due to the inability of XRD to accurately locate hydrogen atoms, the local structures around framework hydrogen are usually poorly characterized even if the overall framework has been accurately determined. 1H solid-state NMR (SSNMR) spectroscopy should, in principle, be used as a complementary method to XRD for characterizing hydrogen local environments. However, the spectral resolution of 1H SSNMR is severely limited by the strong 1H–1H homonuclear dipolar coupling. In this work, we demonstrate that high-resolution 1H MAS spectra of MOF-based material can be obtained by ultrafast sample spinning at high magnetic field in combination with isotopic dilution. In particular, we examined an important MOF, microporous α-Mg3(HCOO)6 and α-Mg3(HCOO)6 in the presence of several guest species. All six chemically very similar,...

High-quality solid-state (17)O (I=5/2) NMR spectra can be successfully obtained for paramagnetic coordination compounds in which oxygen atoms are directly bonded to the paramagnetic metal centers. For complexes containing V(III) (S=1), Cu(II) (S=1/2), and Mn(III) (S=2) metal centers, the (17)O isotropic paramagnetic shifts were found to span a range of more than 10,000 ppm. In several cases, high-resolution (17)O NMR spectra were recorded under very fast magic-angle spinning (MAS) conditions at 21.1 T. Quantum-chemical computations using density functional theory (DFT) qualitatively reproduced the experimental (17)O hyperfine shift tensors.

The solvent free reaction of Zn(OAc)2 with an imidazole ligand resulted in a 1-dimensional (1D) chain structure with the formula [Zn(Im)(HIm)2(OAc)] (Im = imidazolate, HIm = imidazole, OAc = carboxylate) (1). The results by kinetic experiments suggest that (1) likely evolves from an unidentified metastable phase. This new 1D chain precursor (1) is a quaternary system comprising Zn, Im, OAc and HIm. We have used this 1D compound as a single precursor to prepare 3-dimensional (3D) Zn(Im)2 frameworks. Specifically, two Zn(Im)2 frameworks with known zni and coi topologies were prepared via thermal-mediated transformation when heated in an open atmosphere and in a closed vessel, respectively. In an open atmosphere, the kinetic experiments confirmed the rapid phase transformation from (1) to zni without formation of an intermediate phase. In contrast, in the formation process of coi in a closed vessel, phase transformation from (1) to zni and immediately from zni to coi was observed. Thus, in a closed vessel, the released molecules, HOAc and HIm, were occluded in the framework, which may together exert a cooperative structure-directing effect on the formation of the coi framework. Thus, a single precursor approach was established for the synthesis of ZIFs. The present work represents the first example of transforming a 1D coordination polymer into 3D ZIF framework structures.

α-Magnesium formate [α-Mg3(HCOO)6], a representative lightweight Mg-based metal–organic framework (MOF), has the desirable properties of permanent porosity, unique stability and adsorption capacities for small molecules. Using in situ infrared (IR) and Raman spectroscopy, we investigated the structure and stability of the α-Mg3(HCOO)6 framework at high pressures up to 13 GPa. We found that the framework structure was chemically stable under compression, while an irreversible crystal-to-crystal structural transition was observed above 2 GPa. This new phase is likely isostructural with microporous γ-Mg3(HCOO)6. In contrast, the α-Mg3(HCOO)6 framework loaded with guest molecules such as dimethylformamide and benzene exhibits higher stability to external pressure. Neither a new crystalline phase nor an amorphous material was observed under pressure up to 13 GPa.

Formation of molecular sieve SAPO-34 has been examined under vapor-phase transport (VPT) conditions. Powder XRD, SEM/EDX, and solid-state NMR were used to follow the evolution of gel samples as a function of crystallization time. The results indicate that the initial VPT dry gel is a mixture of an amorphous material (major component) and a dense phase (minor component). The amorphous material is aluminophosphate in nature, but its structure is not suitable for transformation into SAPO-34 since it only has octahedral Al. Introducing morpholine (the structure directing agent) onto the surface of the dry gel via a vapor phase leads to changes in the structure of the amorphous phase as is evidenced by the conversion of octahedral Al into the tetrahedral Al sites. The dense phase is transformed into the tridymite phase. Upon further heating under VPT conditions, the equilibrium between tridymite and amorphous phases shifts to the amorphous material which is subsequently reorganized to form SAPO-34. The 29Si NMR results show that Si was incorporated into the framework at a later stage of crystallization via the formation of aluminosilicates. Catalytic tests indicate that the SAPO-34 product obtained by the VPT method had a longer lifetime for 100% methanol conversion and similar product selectivity to the SAPO-34 prepared by the normal hydrothermal synthesis.

Superstructures, combining nanoscopic constituents into micrometer-size assemblies, have a great potential for utilization of the size-dependent quantum-confinement properties in multifunctional electronic and optoelectronic devices. Two diverse superstructures of nanoscopic CdSe were prepared using solvothermal conversion of the same cadmium selenophenolate precursor (Me4N)2[Cd(SePh)4]: the first is a superlattice of monodisperse [Cd54Se32(SePh)48(dmf)4]4– nanoclusters; the second is a unique porous CdSe crystal. Nanoclusters were crystallized as cubic crystals (≤0.5 mm in size) after solvothermal treatment at 200 °C in DMF. UV–vis absorption and PLE spectra of the reported nanoclusters are consistent with previously established trends for the known families of tetrahedral CdSe frameworks. In contrast to these, results of PL spectra are rather unexpected, as distinct room temperature emission is observed both in solution and in the solid state. The porous CdSe crystals were isolated as red hexagonal pris...

We study the effects of loading and nature of the zeolitic framework in the trans ⇌ gauche equilibrium of 1,1,2-trichloroethane (TCE) in zeolites with Faujasite (FAU) structure including sodium Y (Na-Y) and siliceous Y (Si-Y). TCE is used as a prototype molecule for the study of zeolite–chlorinated hydrocarbon interactions that determine conformational equilibrium. Conformational changes of TCE were sampled using empirical force fields and quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) in combination with replica exchange molecular dynamics (REMD). The population ratio of the conformers at high loading was compared with that found by Fourier transform (FT)-Raman spectroscopy and the results are in very good agreement. Comparison between the infinitely dilute limit of loading, and higher loading shows that the population ratio of the conformers at equilibrium depends strongly on the Si/Al ratio and consequently, the presence of charge compensating cations as well as the loading. At very low loading, in both Na-Y and Si-Y the population of the trans conformer is the largest with the exception of the empirical modeling that predicts the gauche conformer to be dominant in Na-Y. At the higher loading, in Na-Y the population the gauche conformer constitutes the great majority. In Si-Y the population of the trans conformer continues to dominate but the percentage of the gauche conformer increases substantially relative to the loading at the infinitely dilute limit. Such different conformational behaviors provide insight into the factors responsible for diffusion mechanisms and adsorption energies in the FAU-type zeolitic frameworks.

We introduce a dip-coating method for preparing self-assembled monolayers (SAMs) of octadecylphosphonic acid (OPA) on hydrophilic substrates by selecting anisole (methoxybenzene) as the solvent, which has a dielectric constant of 4.3. We demonstrate that full-coverage OPA SAMs are formed in a couple of seconds on a cleaved mica substrate upon its dipping in a 1 mM OPA solution in anisole. In order to develop applications of this extremely rapid coating approach in surface engineering, we investigate the thermal stability of OPA SAMs dip-coated on a UV/ozone-cleaned aluminum film using water contact angle measurements and time-of-flight secondary ion mass spectrometry. It was clarified that the OPA SAMs annealed in air at up to 200 °C exhibited excellent hydrophobicity and the degradation mechanism is oxidation of the alkyl chains.

Here we report the structure and optical properties of a new Cu–cysteamine complex (Cu–Cy) with a formula of Cu3Cl(SR)2 (R = CH2CH2NH2). This Cu–Cy has a different structure from a previous Cu–Cy complex, in which both thio and amine groups from cysteamine bond with copper ions. Single-crystal X-ray diffraction and solid-state nuclear magnetic resonance results show that the oxidation state of copper in Cu3Cl(SR)2 is +1 rather than +2. Further, Cu3Cl(SR)2 has been observed to show intense photoluminescence and X-ray excited luminescence. More interesting is that Cu3Cl(SR)2 particles can produce singlet oxygen under irradiation by light or X-ray. This indicates that Cu3Cl(SR)2 is a new photosensitizer that can be used for deep cancer treatment as X-ray can penetrate soft tissues. All these findings mean that Cu3Cl(SR)2 is a new material with potential applications for lighting, radiation detection and cancer treatment.

Molecular sieves have been scientifically and industrially important materials since their discovery. These porous, crystalline networks of tetrahedrally coordinated atoms bridged by oxygen are known as excellent catalysts. The framework of the aluminophosphate family of molecular sieves is itself non-catalytic, but through heteroatomic substitution these materials can diversify into, for example, the silicoaluminophosphate (SAPO) family of heterogeneous acid catalysts. Research into the methods by which these substitutions occur, as discoveries can lead to refined control over material property and function. SAPO-5 was chosen as model system of study. 27 Al, 29 Si and 31 P solid state NMR and PXRD were used as the primary methods of investigation. The SAPO-5 study determined that the dry gel conversion (DGC) methods of steam assisted conversion (SAC) and vapor phase transport (VPT) follow similar reaction pathways. After an initial difference caused by the lack of organic structure directing agent in the gel for the VPT method, crystallization is similar between methods, and silicon incorporation results in two populations of silicon sites. One represents isolated Si(OAl) 4 species well incorporated into the framework, while the other represents silica islands within the framework. The initial core of the nuclei is AlPO 4 in nature and the Si is gradually incorporated into the lattice as the crystals grow. The vapor phase silicon uptake (VPSU) method provides a contrast to this data, inducing nucleation that occurs concurrently with Si incorporation and producing only isolated Si(OAl) 4 species.

The crystallization of microporous material SAPO-37 was studied under hydrothermal synthesis (HTS) and dry gel conversion (DGC) conditions. The evolution of the intermediate phases as a function of crystallization time was followed by several techniques including PXRD, SEM, AFM, and solid-state NMR. For DGC, SAPO-37 crystallizes from a semi-crystalline layered precursor containing large pores and sodalite cages, whose structure is held by weak nonbonding interactions. Si atoms are only incorporated in the later stage of the crystallization via the formation of aluminosilicate species. Under HTS conditions, the crystallization pathway of SAPO-37 is somewhat similar to that for DGC. The AFM data suggest that the crystal growth mechanism is “birth and spread”, and the final SAPO-37 crystals have rough (1 1 1) surfaces terminated by different structural building units. The findings of the present work provide new physical insights into the formation of SAPO-37.

The pressure-induced anomalously high AC conductivity of zeolite NaA mixed with water was measured by impedance spectroscopy at various water/zeolite ratios. The conductivity reaches a maximum value at 0.9–1.4 GPa with increasing water content of up to 20 wt.% in NaA + water. The high ionic conductivity of NaA compressed in water is interpreted to result from cation diffusion in the quasi-liquid Na+–H2O intra-channel system enhanced by the filling of additional H2O sites. The pressure range of anomalously high AC conductivity in NaA enlarges towards higher pressures with decrease of the water/zeolite ratio. An abrupt drop in conductivity observed at P > 1.5 GPa appears to be associated with freezing of intra-channel water. After pressure release, the overhydrated state of the zeolite kept in a closed container can be preserved for a long time, providing abnormally high conductivity which is comparable with that of Na+ β-alumina.

Germanium-73 is an extremely challenging nucleus to examine by NMR spectroscopy due to its unfavorable NMR properties. Through the use of an ultrahigh (21.1 T) magnetic field, a systematic study of a series of simple organogermanes was carried out. In those cases for which X-ray structural data were available, correlations were drawn between the NMR parameters and structural metrics. These data were combined with DFT calculations to obtain insight into the structures of several compounds with unknown crystal structures.