Multinuclear Magic Angle Spinning Research Articles

In Situ Multinuclear Magic-Angle Spinning NMR: Monitoring Crystallization of Molecular Sieve AlPO4-11 in Real Time.

Molecular sieves are crystalline three-dimensional frameworks with well-defined channels and cavities. They have been widely used in industry for many applications such as gas separation/purification, ion exchange, and catalysis. Obviously, understanding the formation mechanisms is fundamentally important. High-resolution solid-state NMR spectroscopy is a powerful method for the study of molecular sieves. However, due to technical challenges, the vast majority of the high-resolution solid-state NMR studies on molecular sieve crystallization are ex situ. In the present work, using a new commercially available NMR rotor that can withhold high pressure and high temperature, we examined the formation of molecular sieve AlPO4-11 under dry gel conversion conditions by in situ multinuclear (1H, 27Al, 31P, and 13C) magic-angle spinning (MAS) solid-state NMR. In situ high-resolution NMR spectra obtained as a function of heating time provide much insights underlying the crystallization mechanism of AlPO4-11. Specifically, in situ 27Al and 31P MAS NMR along with 1H → 31P cross-polarization (CP) MAS NMR were used to monitor the evolution of the local environments of framework Al and P, in situ 1H → 13C CP MAS NMR to follow the behavior of the organic structure directing agent, and in situ 1H MAS NMR to unveil the effect of water content on crystallization kinetics. The in situ MAS NMR results lead to a better understanding of the formation of AlPO4-11.

Discovering the Solid-State Secrets of Lorlatinib by NMR Crystallography: To Hydrogen Bond or not to Hydrogen Bond

Lorlatinib is an active pharmaceutical ingredient (API) used in the treatment of lung cancer. Here, an NMR crystallography analysis is presented whereby the single-crystal X-ray diffraction structure (CSD: 2205098) determination is complemented by multinuclear (1H, 13C, 14/15N, 19F) magic-angle spinning (MAS) solid-state NMR and gauge-including projector augmented wave (GIPAW) calculation of NMR chemical shifts. Lorlatinib crystallises in the P21 space group, with two distinct molecules in the asymmetric unit cell, Z′ = 2. Three of the four NH2 hydrogen atoms form intermolecular hydrogen bonds, N30-H…N15 between the two distinct molecules and N30-H…O2 between two equivalent molecules. This is reflected in one of the NH21H chemical shifts being significantly lower, 4.0 ppm compared to 7.0 ppm. Two-dimensional 1H–13C, 14N-1H and 1H (double-quantum, DQ)-1H (single-quantum, SQ) MAS NMR spectra are presented. The 1H resonances are assigned and specific HH proximities corresponding to the observed DQ peaks are identified. The resolution enhancement at a 1H Larmor frequency of 1 GHz as compared to 500 or 600 MHz is demonstrated.

A novel multinuclear solid-state NMR approach for the characterization of kidney stones.

The spectroscopic study of pathological calcifications (including kidney stones) is extremely rich and helps to improve the understanding of the physical and chemical processes associated with their formation. While Fourier transform infrared (FTIR) imaging and optical/electron microscopies are routine techniques in hospitals, there has been a dearth of solid-state NMR studies introduced into this area of medical research, probably due to the scarcity of this analytical technique in hospital facilities. This work introduces effective multinuclear and multidimensional solid-state NMR methodologies to study the complex chemical and structural properties characterizing kidney stone composition. As a basis for comparison, three hydrates (, 2 and 3) of calcium oxalate are examined along with nine representative kidney stones. The multinuclear magic angle spinning (MAS) NMR approach adopted investigates the , , and nuclei, with the and MAS NMR data able to be readily deconvoluted into the constituent elements associated with the different oxalates and organics present. For the first time, the full interpretation of highly resolved NMR spectra is presented for the three hydrates, based on the structure and local dynamics. The corresponding MAS NMR data indicates the presence of low-level inorganic phosphate species; however, the complexity of these data make the precise identification of the phases difficult to assign. This work provides physicians, urologists and nephrologists with additional avenues of spectroscopic investigation to interrogate this complex medical dilemma that requires real, multitechnique approaches to generate effective outcomes.

Fingerprinting the Hydration Products of Hydraulic Binders Using Snapshots from Time-Resolved In Situ Multinuclear MAS NMR Spectroscopy

The very early hydration behavior of a hydraulic binder phase, ye’elimite, Ca4Al6O12SO4, in the absence and in the presence of calcium sulfate, has been investigated. A time-resolved in situ multinuclear magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic suite involving 1H and 27Al MAS as well as two-dimensional 27Al multiple quantum MAS (MQMAS) experiments has been employed to detect the transient species and to govern the sequence of hydration reactions and the subsequent formation of the hydration products. The results of the study show that the rates of formation of ye’elimite hydration products vary substantially according to the absence or the presence of calcium sulfate. Hydrated calcium sulfoaluminate phases such as ettringite and monosulfate as well as aluminum hydroxide gel have been detected during the various stages of hydration. The direct observation of various transient species during the hydration stages of calcium aluminates and calcium sulfoaluminates illustrates the potential of a newly designed time-resolved in situ 1H MAS NMR experimental approach for fingerprinting phases and offers significant advantages over other established techniques in detecting transient species.

Prominence of the Instability of a Stabilizing Agent in the Changes in Physical State of a Hybrid Nanomaterial.

Shaping ability of hybrid nanomaterials is a key point for their further use in devices. It is therefore crucial to control it. To this end, it is necessary that the macroscopic properties of the material remain constant over time. Here, we evidence by multinuclear Magic-Angle Spinning Nuclear Magnetic Resonance spectroscopic study including 17 O isotope exchange that for a ZnO-alkylamine hybrid material, the partial carbonation of amine into ammonium carbamate molecules is behind the conversion from highly viscous liquid to a powdery solid when exposed to air. This carbonation induces modification and reorganization of the organic shell around the nanocrystals and affects significantly the macroscopic properties of the material such as it physical state, its solubility and colloidal stability. This study, straightforwardly extendable, highlights that the nature of the functional chemical group allowing connecting the stabilizing agent (SA) to the surface of the nanoparticles is of tremendous importance especially if the SA is reactive with molecules present in the environment.

Investigation of structure and dynamics in a photochromic molecular crystal by NMR crystallography.

A photochromic anil, N-(3,5-di-t-butylsalicylidene)-4-amino-pyridine, has been studied by single-crystal X-ray diffraction, multinuclear magic-angle spinning NMR, and first-principles density functional theory (DFT) calculations. Interpretation of the solid-state NMR data on the basis of calculated chemical shifts confirms the structure is primarily composed of molecules in the ground-state enol tautomer, whereas thermally activated cis-keto and photoisomerised trans-keto states exist as low-level defects with populations that are too low to detect experimentally. Variable temperature 13 C NMR data reveal evidence for solid-state dynamics, which is found to be associated with fast rotational motion of t-butyl groups and 180° flips of the pyridine ring, contrasting the time-averaged structure obtained by X-ray diffraction. Comparison of calculated chemical shifts for the full crystal structure and an isolated molecule also reveals evidence for an intermolecular hydrogen bond involving the pyridine ring and an adjacent imine carbon, which facilitates the flipping motion. The DFT calculations also reveal that the molecular conformation in the crystal structure is very close to the energetic minimum for an isolated molecule, indicating that the ring dynamics arise as a result of considerable steric freedom of the pyridine ring and which also allows the molecule to adopt a favourable conformation for photochromism.

Stability of NASICON materials against water and CO2 uptake

The stability in ambient conditions of a scandium-based NASICON material, Na3.4Sc2Si0.4P2.6O12, was investigated using impedance spectroscopy, thermogravimetry/differential scanning calorimetry (TG/DSC) and multinuclear magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The presence of H2O and CO2 in samples stored in ambient air could be evidenced as well as its impact on the ionic conductivity of the samples.The detected amounts of water and CO2 in the samples had no influence on the measured conductivities at room temperature, which confirmed the absence of protonic conduction in hydrated samples. A loss of conductivity during heating of hydrated samples was due to a loss of contact between the ceramic and the electrode used for the conductivity measurement.The recommendation for handling of NASICON-type materials is therefore: samples require storage in an Ar-filled glove box or in a dry environment to avoid artefacts during high temperature measurements. Nevertheless, the stability of the NASICON-type materials is confirmed since their conductivity is not affected by the moisture.

Ternary silicides ScIr4Si2 and RERh4Si2 (RE = Sc, Y, Tb-Lu) and quaternary derivatives RERh4Si2–xSnx (RE = Y, Nd, Sm, Gd-Lu) – structure, chemical bonding, and solid state NMR spectroscopy

Abstract The silicides ScIr4Si2 and RERh4Si2 (RE=Sc, Y, Tb-Lu) and silicide stannides RERh4Si2–x Sn x (RE=Y, Nd, Sm, Gd-Lu) were synthesized from the elements by arc-melting and subsequent annealing. The new compounds crystallize with the orthorhombic YRh4Ge2 type structure, space group Pnma. They were characterized by X-ray powder patterns and several structures were refined from single crystal X-ray diffractometer data. The main structural motifs of this series of silicides are tricapped trigonal prisms formed by the transition metal and rare earth atoms. One of the two crystallographically independent silicon sites allows for formation of solid solutions with tin, exemplarily studied for ErRh4Si2–x Sn x . Electronic structure calculations reveal strong covalent Rh–Si bonding as the main stability factor. Multinuclear (29Si, 45Sc, and 89Y) magic-angle spinning (MAS) NMR spectra of the structure representatives with diamagnetic rare-earth elements (Sc, Y, Lu) are found to be consistent with the crystallographic data and specifically confirm the selective substitution of Sn in the Si2 sites in the quaternary compounds YRh4SiSn and LuRh4SiSn.

Structure and Interactions in Polybenzimidazole Composite Membranes for High-Temperature Polymer Fuel Cells: A Full Multinuclear Solid-State NMR Study

Fabrication of composite membranes including inorganic or hybrid fillers into polybenzimidazole (PBI) membranes is a promising strategy for improving the performance of a membrane-electrode assembly (MEA) for high-temperature fuel cells. To this aim, a full understanding of the structure and interactions in such a complex system, which includes polymer, filler, and phosphoric acid, is mandatory. In this paper, we used multinuclear magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy to investigate the inclusion of inorganic and hybrid mesoporous fillers into a pyridine-based polybenzimidazole (PBI_5N) matrix and the effects of the subsequent H3PO4 doping. Composite membranes were prepared through an innovative spray deposition method, with 30 wt % of filler loading and SBA-15 or propylsulfonic-functionalized SBA-15-type silicas as filler. 13C CP MAS NMR experiments showed the structural changes induced by the acid doping on the polymer backbone. 31P(1H) 2D heteronuclear correlation experiments confirmed strong interactions between H3PO4 molecules and imidazole protons through a hydrogen-bonding network. 29Si(1H) CP MAS experiments revealed different interactions between acid and filler particles, depending on the filler type. Here, for the first time, a complete understanding of the interactions among polymer, filler, and phosphoric acid is provided. We demonstrate that a fully inorganic mesoporous filler seems to be more suitable with respect to the hybrid homologues for increasing the proton conductivity of PBI, because of its higher affinity with H3PO4. We gave evidence of a possible proton conductivity inside the mesoporous structure of SBA-15, which became hindered in the propylsulfonic-functionalized silicas due to the presence of −SO3H moieties.

NMR crystallography of an oxovanadium(V) complex by an approach combining multinuclear magic angle spinning NMR, DFT, and spin dynamics simulations.

Bioinorganic vanadium(V) solids are often challenging for structural analysis. Here, we explore an NMR crystallography approach involving multinuclear (13) C/(51) V solid-state NMR spectroscopy, density functional theory (DFT), and spin dynamics numerical simulations, for the spectral assignment and the 3D structural analysis of an isotopically unmodified oxovanadium(V) complex, containing 17 crystallographically inequivalent (13) C sites. In particular, we report the first NMR determination of C-V distances. So far, the NMR observation of (13) C-(51) V proximities has been precluded by the specification of commercial NMR probes, which cannot be tuned simultaneously to the close Larmor frequencies of these isotopes (100.6 and 105.2 MHz for (13) C and (51) V, respectively, at 9.4 T). By combining DFT calculations and (13) C-(51) V NMR experiments, we propose a complete assignment of the (13) C spectrum of this oxovanadium(V) complex. Furthermore, we show how (13) C-(51) V distances can be quantitatively estimated.

Effect of demixing and coarsening on the energetics of poly(boro)silazane-derived amorphous Si–(B–)C–N ceramics

Novel poly(boro)silazane-derived Si–(B–)C–N ceramics pyrolyzed at 1100 and 1400 °C were analyzed by multinuclear magic-angle spinning nuclear magnetic resonance spectroscopy and high-temperature oxidative solution calorimetry to investigate the energetic effects of nanodomain structure evolution at two critical pyrolysis temperatures. Like other Si–B–C–N ceramics, increasing pyrolysis temperatures result in the demixing of SiC x N 4− x mixed bond environments into SiC 4 and SiN 4 tetrahedra, interdomain bond cleavage and nanodomain coarsening. Concurrent demixing and domain coarsening, processes detrimental to these ceramics, were found to be energetically stabilizing.

Influence of strontium substitution on structure and crystallisation of Bioglass® 45S5

The changes in the structure of 45S5 Bioglass® and its heat-treated versions upon SrO substitution were investigated by solid-state multinuclear magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray diffraction and differential scanning calorimetry. A series of the melt-derived glasses with SrO gradually substituted for calcium (0, 25, 50, 75 and 100%) on a molar basis was synthesised. The glass transition temperature, Tg, and crystallisation temperature decreased upon SrO substitution. Glasses with 75 and 100% of SrO substitution showed a minor crystalline phase. 31P MAS-NMR showed that phosphorus is present as orthophosphate in the entire glass series; 29Si MAS-NMR data showed a predominantly Q2 silicate network. A small step change in the position of the 31P and 29Si MAS-NMR signals found between the glasses with 25 and 50% of SrO substitution is attributed due to an increase in the ring-type fraction of the Q2 silicate glass over the mainly chain topology in the original 45S5 glass. On heat treatment combeite (Na2Ca2Si3O9) and combeite-type (Na2CaSi2O6) silicate phases were identified. For glasses with increasing SrO contents the equivalent Sr2+ substituted phases were formed (viz. Na2Sr2Si3O9 and Na2SrSi2O6) above 600 °C. The polymerisation degree of phosphorus increased and in addition to orthophosphate amorphous pyro- and meta-phosphate species were observed on heat treatment between 600 and 650 °C, the amount of which reduced with SrO substitution. Above 800 °C, changes in 31P MAS-NMR spectra suggested that several phosphate containing phases crystallised and the fraction of the remaining glass was below the detection limit. In contrast to the SrO containing glasses, in the original 45S5 composition a significant fraction of phosphorus remained amorphous even after heat treatment at temperatures above 800 °C.

Study of the cytotoxicity and particle action in human cancer cells of titanocene-functionalized materials with potential application against tumors

Titanocene dichloride [Ti(η 5-C 5H 5) 2Cl 2] ( 1), has been grafted onto dehydrated hydroxyapatite (HAP), Al 2O 3 and two mesoporous silicas MSU-2 (Michigan State University Silica type 2) and HMS (Hexagonal Mesoporous Silica), to give the novel materials HAP/[Ti(η 5-C 5H 5) 2Cl 2] ( S1) (1.01 wt.% Ti), Al 2O 3/[Ti(η 5-C 5H 5) 2Cl 2] ( S2) (2.36 wt.% Ti), HMS/[Ti(η 5-C 5H 5) 2Cl 2] ( S3) (0.75 wt.% Ti) and MSU-2/[Ti(η 5-C 5H 5) 2Cl 2] ( S4) (0.74 wt.% Ti), which have been characterized by powder X-ray diffraction, X-ray fluorescence, nitrogen gas sorption, multinuclear magic angle spinning NMR spectroscopy, IR spectroscopy, thermogravimetry analysis, UV spectroscopy, scanning electronic microscopy and transmission electronic microscopy. The cytotoxicity of the titanocene-functionalized materials toward human cancer cell lines from five different histogenic origins: 8505 C (anaplastic thyroid cancer), A253 (head and neck cancer), A549 (lung carcinoma), A2780 (ovarian cancer) and DLD-1 (colon cancer) has been determined. M 50 values (quantity of material needed to inhibit normal cell growth by 50%) and Ti-M 50 values (quantity of anchored titanium needed to inhibit normal cell growth by 50%) indicate that the activity of S1– S4 against studied human cancer cells depended on the surface type as well as on the cell line. In addition, studies on the titanocene release and the interaction of the materials S1– S4 with DNA show that the cytotoxic activity may be due to particle action, because no release of titanium complexes has been observed in physiological conditions, while electrostatic interactions of titanocene-functionalized particles with DNA have been observed.

Exploiting Nanospace for Asymmetric Catalysis: Confinement of Immobilized, Single-Site Chiral Catalysts Enhances Enantioselectivity

In the mid-1990s, it became possible to prepare high-area silicas having pore diameters controllably adjustable in the range ca. 20-200 Å. Moreover, the inner walls of these nanoporous solids could be functionalized to yield single-site, chiral, catalytically active organometallic centers, the precise structures of which could be determined using in situ X-ray absorption and FTIR and multinuclear magic angle spinning (MAS) NMR spectroscopy. This approach opened up the prospect of performing heterogeneous enantioselective conversions in a novel manner, under the spatial restrictions imposed by the nanocavities within which the reactions occur. In particular, it suggested an alternative method for preparing pharmaceutically and agrochemically useful asymmetric products by capitalizing on the notion, initially tentatively perceived, that spatial confinement of prochiral reactants (and transition states formed at the chiral active center) would provide an altogether new method of boosting the enantioselectivity of the anchored chiral catalyst. Initially, we anchored chiral single-site heterogeneous catalysts to nanopores covalently via a ligand attached to Pd(II) or Rh(I) centers. Later, we employed a more convenient and cheaper electrostatic method, relying in part on strong hydrogen bonding. This Account provides many examples of these processes, encompassing hydrogenations, oxidations, and aminations. Of particular note is the facile synthesis from methyl benzoylformate of methyl mandelate, which is a precursor in the synthesis of pemoline, a stimulant of the central nervous system; our procedure offers several viable methods for reducing ketocarboxylic acids. In addition to relying on earlier (synchrotron-based) in situ techniques for characterizing catalysts, we have constructed experimental procedures involving robotically controlled catalytic reactors that allow the kinetics of conversion and enantioselectivity to be monitored continually, and we have access to sophisticated, high-sensitivity chiral chromatographic facilities and automated high-throughput combinatorial test rigs so as to optimize the reaction conditions (e.g., H(2) pressure, temperature, time on-stream, pH, and choice of ligand and central metal ion) for high enantioselectivity. This Account reports our discoveries of selective hydrogenations and aminations of synthetic, pharmaceutical, and biological significance, and the findings of other researchers who have achieved similar success in oxidations, dehydrations, cyclopropanations, and hydroformylations. Although the practical advantages and broad general principles governing the enhancement of enantioselectivity through spatial confinement are clear, we require a deeper theoretical understanding of the details pertaining to the phenomenology involved, particularly through molecular dynamics simulations. Ample scope exists for the general exploitation of nanospace in asymmetric hydrogenations with transition metal complexes and for its deployment for the formation of C-N, C-C, C-O, C-S, and other bonds.

Olefin Metathesis over Heterogeneous Catalysts: Interfacial Interaction between Mo Species and a Hβ−Al2O3 Composite Support

The effect of molybdenum content on the structure and performance of Mo/Hβ−Al2O3 catalysts in olefin metathesis was examined. The optimal performance was obtained with a catalyst of 4−6 wt % Mo on a composite support of 70% Hβ zeolite and 30% Al2O3. The interfacial interaction between the Mo species and the Hβ−Al2O3 composite support was carefully studied by X-ray diffraction (XRD), N2 adsorption, and multinuclear magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. XRD and N2 adsorption results indicate that some interactions may occur between the Mo species and the composite support during the sample preparation. 27Al and 29Si MAS NMR spectra show that this kind of interaction becomes more severe and leads to the dealumination of the framework and subsequent appearance of aluminum molybdate with increasing Mo loadings. Two-dimensional 27Al MQ MAS NMR spectra further demonstrate that the framework Al on Hβ zeolite at the specific T sites could be preferentially extracted upon Mo loading, which may result in the appropriate Brønsted acidity on the support as evidenced by the quantitative 1H MAS NMR measurements. A moderate interaction of Mo species with the support and the proper acidity may be advantageous for the cross-metathesis of ethene and 2-butene to propene over heterogeneous catalysts.

Structure determination of β-Pb2ZnF6 by coupling multinuclear solid state NMR, powder XRD and ab initio calculations

The results from one-dimensional multinuclear (19F, 207Pb and 67Zn) magic-angle spinning nuclear magnetic resonance experiments combined with the use of the ISODISPLACE program allow for the space group determination of beta-Pb2ZnF6 (no. 138 P4(2)/ncm). The structure was refined from X-ray powder diffraction data (a = 5.633 (1) A and c = 16.247 (1) A, Z = 4). beta-Pb2ZnF6 has one six-fold coordinated Zn, one eleven-fold coordinated Pb and five F non-equivalent crystallographic sites and is built from alternated layers parallel to the (a, b) plane; tilted ZnF4(2-) layers of corner sharing ZnF6(4-) octahedra and FPb+ layers of edge sharing FPb4(7+) tetrahedra. The structure of beta-Pb2ZnF6 was then optimized using the ab initio code WIEN2k and the calculated 67Zn EFG is in agreement with the NMR results. 19F-19F proximities and 19F-207Pb connectivities were evidenced using through-space and through-bond NMR correlation experiments, respectively, and support the proposed structure. 19F-207Pb J-coupling was also used to select fluorine resonances depending on the number of neighbouring lead ions, leading to an unambiguous assignment of the different 19F resonances.

Structure of (NH4)3GaF6 Investigated by Multinuclear Magic-Angle Spinning NMR Spectroscopy in Comparison with Rietveld Refinement

The structure of ammonium gallium cryolite (NH(4))(3)GaF(6) was investigated by (19)F and (69,71)Ga magic-angle spinning (MAS) NMR in comparison with X-ray powder diffraction followed by Rietveld refinement. In agreement with previous thermodynamic measurements, NMR experiments on (NH(4))(3)GaF(6) support the model of rigid GaF(6) octahedra. At high spinning speeds (30 kHz), the scalar coupling between the six equivalent (19)F nuclei and (69,71)Ga can be directly observed in the powder spectra. The coupling constants are J(19)F(69)Ga = 197 Hz and J(19)F(71)Ga = 264 Hz. To explain the (71)Ga spectra recorded at 3 kHz a small distribution of quadrupolar frequencies has to be included. The spread of the spinning sidebands hints to a largest nu(Q) value of 28 kHz for (71)Ga. This can be explained by the occurrence of highly symmetric GaF(6) octahedra, which are tilted against the surrounding atoms. In addition, the incomplete motional excitation does not average out the quadrupolar effects. NMR findings are in discrepancy to those of Rietveld refinement. As result it appears that X-ray diffraction is not sensitive enough to deliver proper results.

NMR Study of a Rare-Earth Aluminoborosilicate Glass with Varying CaO-to-Na2O Ratio

The effect of substituting two Na+ by one Ca2+ in a rare-earth aluminoborosilicate glass is investigated by multinuclear magic-angle spinning (MAS) and multiple-quantum (MQ)MAS nuclear magnetic resonance (NMR) spectroscopy. Quantitative analysis of the 23Na and 27Al MAS/MQMAS data along with the 11B MAS NMR data provides complementary information enabling to cast light on different structural key points. A strong decrease of the N4 = BO4/(BO3 + BO4) ratio is observed consecutively to this substitution, indicating that sodium is more favorable than calcium to the formation of BO4 units. The experimental N4 ratio is compared to the Dell and Bray model prediction and it is shown that several adjustments, due to the presence in our glass of Nd and Zr, are necessary to obtain acceptable agreement with experimental data. 29Si MAS NMR data also put in evidence an effect of the substitution on the polymerization degree. Glass in glass phase separation is clearly detected when the ratio of CaO to Na2O is greater than 1 and a different evolution of NMR parameters is observed for the ratio of CaO to Na2O being less than or equal to 1. Concerning aluminum charge compensation, it is demonstrated that, as long as no phase separation is detected, the negative charge of AlO4− entities is almost exclusively balanced by sodium cations. Finally, changes of the sodium ions organization within the glass network are also evidenced by spin–lattice relaxation and spin echo decay measurements.

Solid State MAS-NMR and FTIR Study of Barium Containing Alumino-Silicate Glasses

The glass based on a 1.5SiO2-Al2O3-0.5P2O5-CaO-0.67CaF2 composition was produced and substituted gradually by barium. The structure of the glasses was studied by multinuclear Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) and Fourier Transform Infrared Spectroscopy (FTIR). It was indicated by 29Si and 31P MAS-NMR spectra that silicon was present as Q4 (4Al) and Q3 (3Al) species and phosphorus was in a Q1 pyrophosphate environment. 29Al MAS-NMR spectra showed that four fold coordinated aluminum Al (IV) was the dominant species with a second peak assigned to octahedral aluminum Al (VI). The 19F spectra suggested that the barium addition caused the formation of Al-F-Ba(n) and F-Ba(n) species. Furthermore, a distribution of silicate network including Si-O-Si stretching (Q4 and Q3) and Si-O-[NBO] (Q3) per SiO4 was reflected by the FTIR study.

Structural and Catalytic Studies of a Trimethyltin Vanadate Coordination Polymer

The organotin vanadate [Me3SnVO3] (1) has been prepared and characterised in the solid state by powder X-ray diffraction (XRD), thermogravimetric analysis, multinuclear magic-angle spinning (MAS) NMR, IR and Raman spectroscopy. The phase purity and structure of microcrystalline 1 were confirmed by carrying out a full Rietveld structural refinement at ambient temperature and from conventional powder XRD. 51V and 119Sn MAS NMR data for compound 1 were in agreement with the predicted structure, showing two equally-abundant, nonequivalent Me3Sn groups and two equally-abundant, nonequivalent vanadium atoms. The compound was applied as a catalyst for the liquid-phase epoxidation of olefins at 55 °C using tert-butyl hydroperoxide (tBuOOH) as the oxidant. The reaction rate for the different substrates followed the order cis-cyclooctene > (R)-(+)-limonene ≅ trans-2-octene > cyclododecene > styrene > 1-octene; the corresponding epoxides were the only observed products. Leaching tests indicated that the catalytic epoxidation of cyclooctene was mainly heterogeneous in nature.