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Although organic mixed ionic–electronic conductors are widely proposed for use in bioelectronics, energy generation/storage and neuromorphic computing, our fundamental understanding of the charge-compensating interactions between the ionic and electronic carriers and the dynamics of ions remains poor, particularly for hydrated devices and on electrochemical cycling. Here we show that operando 23Na and 1H nuclear magnetic resonance (NMR) spectroscopy can quantify cation and water movement during the doping/dedoping of films comprising the widely used mixed conductor poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate) (PEDOT:PSS). A distinct 23Na quadrupolar splitting is observed due to the partial ordering of the PSS chains within the PEDOT:PSS-rich domains, with respect to the substrate. Operando 23Na NMR studies reveal a close-to-linear correlation between the quadrupolar splitting and the charge stored, which is quantitatively explained by a model in which the holes on the PEDOT backbone are bound to the PSS SO3−groups; an increase in hole concentration during doping inversely correlates with the number of Na+ions bound to the PSS chains within the PEDOT-rich ordered domains, leading to a decrease in ions within the ordered regions and a decrease in quadrupolar splitting. The Na+-to-electron coupling efficiency, measured via 23Na NMR intensity changes, is close to 100% when using a 1 M NaCl electrolyte. Operando 1H NMR spectroscopy confirms that the Na+ions injected into/extracted from the wet films are hydrated. These findings shed light on the working principles of organic mixed conductors and demonstrate the utility of operando NMR spectroscopy in revealing structure–property relationships in electroactive polymers.

The enhancing effect of extraframework Al (EFAl) species on the acidity of bridging hydroxyl groups in a steam-calcined faujasite zeolite (ultrastabilized Y, USY) was investigated by in situmonitoring the H/D exchange reaction between benzene and deuterated zeolites by 1H MAS NMR spectroscopy. This exchange reaction involves Brønsted acid sites (BAS) located in sodalite cages and supercages. In a reference faujasite zeolite free from EFAl, both populations of BAS are equally and relatively slowly reactive toward C6H6. In USY, in stark contrast, the H/D exchange of sodalite hydroxyl groups is significantly faster than that of hydroxyl groups located in the faujasite supercages, even though benzene has only access to the supercages. This evidences selective enhancement of BAS near Lewis acidic EFAl species, which according to the NMR findings are located in the faujasite sodalite cages.

Li-O2batteries offer a high theoretical discharge capacity due to the formation of light discharged species such as Li2O2, which fill the porous positive electrode. However, in practice, it is challenging to reach the theoretical capacity and completely utilize the full electrode pore volume during discharge. With the formation of discharge products, the porous medium evolves, and the porosity and tortuosity factor of the positive electrode are altered through shrinkage and clogging of pores. A pore shrinks as solid discharge products accumulate, the pore clogging when it is filled (or when access is blocked). In this study, we investigate the structural evolution of the positive electrode through a combination of experimental and computational techniques. Pulsed field gradient nuclear magnetic resonance results show that the electrode tortuosity factor changes much faster than suggested by the Bruggeman relation (an equation that empirically links the tortuosity factor to the porosity) and that the electrolyte solvent affects the tortuosity factor evolution. The latter is ascribed to the different abilities of solvents to dissolve reaction intermediates, which leads to different discharge product particle sizes: on discharging using 0.5 M LiTFSI in dimethoxyethane, the tortuosity factor increases much faster than for discharging in 0.5 M LiTFSI in tetraglyme. The correlation between a discharge product size and tortuosity factor is studied using a pore network model, which shows that larger discharge products generate more pore clogging. The Knudsen diffusion effect, where collisions of diffusing molecules with pore walls reduce the effective diffusion coefficients, is investigated using a kinetic Monte Carlo model and is found to have an insignificant impact on the effective diffusion coefficient for molecules in pores with diameters above 5 nm, i.e., most of the pores present in the materials investigated here. As a consequence, pore clogging is thought to be the main origin of tortuosity factor evolution.

A key factor for the petroleum potential of source rock is the degree of chemical and physical structure evolution of its kerogen fraction through a range of maturation processes. In this study, various high-field, solid-state NMR methods have been applied to a series of kerogen isolates (type I) over a defined maturity range (vitrinite reflectance R0from 0.98 to 1.86%). Results obtained from 13C MAS NMR show that the sp2/sp3-hybridized carbon ratio of kerogen, here defined as the aromatic/aliphatic ratio, increases with increasing maturity. 1H MAS NMR spectra contain partly overlapping aliphatic and aromatic resonances with distinct transverse relaxation behavior. In Hahn-echo experiments, the aromatic signal decays more slowly than the aliphatic signal, indicating that for these systems, transverse 1H relaxation is rather controlled by local distances between hydrogen atoms than by molecular mobility. Similar relaxation differences are also found in static (nonspinning) 1H Hahn-echo NMR experiments, here used to discriminate between phases with different proton mobilities and/or densities in the kerogen samples and, ultimately, between aromatic and aliphatic fractions. The distributions of the static transverse relaxation time (T2), extracted from the Hahn-echo decays, are characterized by a short-T2peak (∼10 μs) and a long-T2peak (∼100 μs). The ratio between these two peaks correlates well with the aliphatic-to-aromatic signal intensity ratios in MAS NMR spectra of the corresponding kerogen samples, suggesting that a net decrease in kerogen proton density—occurring during maturation—is also reflected by 1H NMR relaxation. For the investigated kerogen isolates, the long-T2peak in the T2distribution can be considered an indicator of aromatic content, which can be directly detected by measuring 1H T2relaxation.

Silicon monoxide is a promising alternative anode material due to its much higher capacity than graphite, and improved cyclability over other Si anodes. An in-depth analysis of the lithium silicide (LixSi) phases that form during lithiation/delithiation of SiO is presented here and the results are compared with pure-Si anodes. A series of anode materials is first prepared by heating amorphous silicon monoxide (a-SiO) at different temperatures, X-ray diffraction and 29Si NMR analysis revealing that they comprise small Si domains that are surrounded by amorphous SiO2, the domain size and crystallinity growing with heat treatment. Inand ex situ7Li and 29Si solid-state NMR combined with detailed electrochemical analysis reveals that a characteristic metallic LixSi phase is formed on lithiating a-SiO with a relatively high Li concentration of x= 3.4–3.5, which is formed/decomposed through a continuous structural evolution involving amorphous phases differing in their degree of Si–Si connectivity. This structural evolution differs from that of pure-Si electrodes where the end member, crystalline Li15Si4, is formed/decomposed through a two-phase reaction. The reaction pathway of SiO depends, however, on the size of the ordered Si domains within the pristine material. When crystalline domains of >3 nm within a SiO2matrix are present, a phase resembling Li15Si4forms, albeit at a higher overpotential. The continuous formation/decomposition of amorphous LixSi phases without the hysteresis and phase change associated with the formation of c-Li15Si4, along with a partially electrochemically active SiO2/lithium silicate buffer layer, are paramount for the good cyclability of a-SiO.

Fluorite-structured Mg–Ti hydrides are interesting for hydrogen storage applications because of their high gravimetric hydrogen storage capacity, and improved (de)hydrogenation kinetics compared to MgH2. In the present study we have investigated the potential catalytic effect of Ni and Si as third element on the siting and mobility of electrochemically loaded deuterium in ball-milled Mg0.63Ti0.27Ni0.10and Mg0.63Ti0.27Si0.10alloys. Magic angle spinning (MAS) 2H NMR reveals that Ni and Si induce new types of deuterium sites in addition to the Mg-rich and Ti-rich sites already present in Mg0.65Ti0.35D1.2. 2D exchange NMR spectroscopy shows a substantial deuterium exchange between the various types of sites, which reflects their close interconnectivity in the crystal structure. Furthermore, the time scale and temperature dependence of the deuterium mobility have been quantified by 1D exchange NMR. The obtained effective residence times for deuterium atoms in the Mg-rich and Ti-rich nanodomains in Mg0.65Ti0.35D1.2, Mg0.63Ti0.27Ni0.10D1.3, and Mg0.63Ti0.27Si0.10D1.1at 300 K are 0.4, 0.3, and 0.8 s, respectively, and the respective apparent activation energies 17, 21, and 27 kJ mol–1. The addition of Ni promotes deuterium mobility inside Mg–Ti hydrides, which is in agreement with the observed catalytic effect of Ni on the electrochemical (de)hydrogenation of these materials.

To understand the catalytic influence of TiF3on the de- and rehydrogenation of ball milled MgH2–TiF3, a detailed study has been performed of the different crystallographic phases of the de- and rehydrogenated materials. Rietveld-refined XRD analysis of the dehydrogenated material indicates the presence of a rutile, nonstoichiometric MgF2–xphase and a hexagonal Mg1–yTiyFzphase. After rehydrogenation three different fluorine environments were found by 19F NMR, which can be attributed to MgF2–x, MgF2–xHx, and MgF2–xdispersed with MgO nanodomains. The remarkable MgF2–xHxphase, which is apparently formed from the nonstoichiometric MgF2–xphase in the dehydrogenated material, may indicate a diffusion pathway of hydrogen within Mg/MgH2–x. Furthermore, the previously found nonstoichiometric MgH2–xphase appears to be metastable as is observed by XRD analysis after long-term storage. TEM with EDX measurements performed for both dehydrogenated and rehydrogenated samples provide information that the nanoparticles are highly crystalline and that the catalyst is homogenously distributed over the sample at a 100 nm length scale. More locally, the fluorine-containing phase is observed mainly at the surface of the Mg and MgH2particles and the Ti-containing species are present throughout the particles, likely as TiH2inclusions in the Mg structure and/or as Mg–Ti–F compound. Additionally, an about 2–5.5 nm MgO layer covers the Mg aggregates. A model of the hydrogen uptake and sample morphology is proposed.

New routes for the preparation of highly active TiO2‐supported Cu and CuZn catalysts have been developed for CO coupling reactions. Slurries of a titania precursor were dip‐coated onto glass beads to obtain either structured mesoporous or non‐porous titania thin films. The Cu and CuZn nanoparticles, synthesized using a reduction by solvent method, were deposited onto calcined films to obtain a Cu loading of 2 wt %. The catalysts were characterized by inductively coupled plasma (ICP) spectroscopy, temperature‐programmed oxidation/reduction (TPO/TPR) techniques, 63Cu nuclear magnetic resonance (NMR) spectroscopy, X‐ray diffraction (XRD), scanning and transmission electron microscopy (S/TEM‐EDX) and X‐ray photo‐electron spectroscopy (XPS). The activity and stability of the catalysts obtained have been studied in the CO Ullmann coupling of 4‐chloropyridine and potassium phenolate. The titania‐supported nanoparticles retained catalyst activity for up to 12 h. However, catalyst deactivation was observed for longer operation times due to oxidation of the Cu nanoparticles. The oxidation rate could be significantly reduced over the CuZn/TiO2catalytic films due to the presence of Zn. The 4‐phenoxypyridine yield was 64 % on the Cu/nonporous TiO2at 120 °C. The highest product yield of 84 % was obtained on the Cu/mesoporous TiO2at 140 °C, corresponding to an initial reaction rate of 104 mmol gcat−1s−1. The activation energy on the Cu/mesoporous TiO2catalyst was found to be (144±5) kJ mol−1, which is close to the value obtained for the reaction over unsupported CuZn nanoparticles (123±3 kJ mol−1) and almost twice the value observed over the catalysts deposited onto the non‐porous TiO2support (75±2 kJ mol−1).

Unsaturated metal coordination sites in metal organic frameworks (MOFs) offer preferential hydrogen adsorption sites. In addition, MOFs can be applied as scaffolds for nano metal hydrides operating at elevated temperatures. For these reasons, the thermal stability of the framework with unsaturated Cu2+coordination sites in a hydrogen atmosphere has been investigated in Cu3(BTC)2. It is found that Cu3(BTC)2irreversibly binds 1.1 wt % of hydrogen at the temperatures between 323 and 423 K and 2 bar H2pressure, which corresponds to three hydrogen atoms per BTC ligand. In accordance, FT-IR and NMR spectroscopy show that the BTC linkers are converted to their acid form, whereas XRD reveals the presence of reduced Cu0metal particles and decomposition of the framework. When designing more strongly interacting MOFs for H2storage applications or as template for light metal hydrides, one has to take possible reduction of the metal centers and the stability of the lattice into account.

Nanostructured magnesium titanium alloys are interesting lightweight materials for chemical hydrogen storage. We have therefore investigated the siting and dynamics of deuterium absorbed in a Mg0.65Ti0.35alloy generated by magnetron cosputtering, and made a comparison to the corresponding features in bulk samples of deuterium-loaded Mg0.65Ti0.35and Mg0.65Sc0.35prepared by ball-milling and melt-casting, respectively. Magic-angle spinning 2H NMR of cosputtered Mg0.65Ti0.35D1.1shows partly resolved signals of deuterium located in nonconductive domains at tetrahedral Mg4and mixed MgnTi4−nsites (4 ppm) and deuterium at Ti4sites in conducting TiD2nanodomains (−29 and −68 ppm). No bulk TiD2signal at −150 ppm is observed, in contrast to what we find in ball-milled Mg0.65Ti0.35D0.65, which is largely phase separated. The deuterium species with shift values of 4 and −29 ppm undergo complete exchange at a subsecond time scale in one- and two-dimensional exchange NMR and must therefore be close together in the lattice. In contrast, deuterium resonating at −68 ppm does not show deuterium exchange and thus appears to be located at more stable sites. The observed deuterium exchange and the reduced Knight shift compared to bulk TiD2are explained using a model with TiD2nanoslabs.

A novel interfacial hybrid epoxidation catalyst was designed with a new immobilization method for homogeneous catalysts by coating an inorganic support with an organic polymer film containing active sites. The titanium silsesquioxane (TiPOSS) complex, which contains a single‐site titanium active center, was immobilized successfully by in‐situ copolymerization on a mesoporous SBA‐15‐supported polystyrene polymer. The resulting hybrid materials exhibit attractive textural properties (highly ordered mesostructure, large specific surface area (>380 m2g−1) and pore volume (≧0.46 cm3g−1)), and high activity in the epoxidation of alkenes. In the epoxidation of cyclooctene with tert‐butyl hydrogen peroxide (TBHP), the hybrid catalysts have rate constants comparable with that of their homogeneous counterpart, and can be recycled at least seven times. They can also catalyze the epoxidation of cyclooctene with aqueous H2O2as the oxidant. In two‐phase reaction media, the catalysts show much higher activity than their homogeneous counterpart due to the hydrophobic environment around the active centers. They behave as interfacial catalysts due to their multifunctionality, that is, the hydrophobicity of polystyrene and the polyhedral oligomeric silsesquioxanes (POSS), and the hydrophilicity of the silica and the mesoporous structure. Combination of the immobilization of homogeneous catalysts on two conventional supports, inorganic solid and organic polymer, is demonstrated to achieve novel heterogeneous catalytic ensembles with the merits of attractive textural properties, tunable surface properties, and optimized environments around the active sites.

Herein we report the synthesis and characterization of hollow silica spheres with a narrow size distribution, uniform wall thickness, and a worm‐like pore structure. The formation of these spheres was monitored by confocal laser scanning microscopy and dynamic light scattering. A model for the molecular build‐up of these silica hollow spheres is derived from these data in combination with studies of the as‐made particles by transmission electron microscopy, scanning electron microscopy, pore size analysis, thermogravimetric analysis, and solid‐state nuclear magnetic resonance. We further demonstrate that these spheres can be used for the encapsulation and subsequent release of different dye molecules.

Crosslinking of artificial latices based on ethylene–propylene copolymers (EPM) and/or ethylene–propylene–diene copolymers (EPDM) has not thoroughly been studied yet. Moreover, crosslinking of EPM and/or EPDM particles is a prerequisite for the formation of a shell using seeded emulsion polymerization of, for example, methyl methacrylate (MMA), as described elsewhere. Therefore, the aim of this article is to improve the general understanding of the chemistry involved in the crosslinking process. This work especially emphasizes the influence of the initiation method, that is, a peroxide or a pulsed electron‐beam, on crosslinking efficiency. All crosslinking efficiencies were obtained after extraction of the soluble polymer by tetrahydrofuran. The incorporation of the coagent, that is, divinylbenzene, into the EPM/EPDM phase was studied on a microscopic level by solid‐state 13C and 1H nuclear magnetic resonance (NMR). Crosslinking of a low molecular weight EPM/EPDM latex requires the presence of a coagent, for example, divinylbenzene, 1,6‐hexanediol diacrylate, or poly(1,2‐butadiene). The efficiency of crosslinking initiated by a pulsed electron‐beam was improved to a great extent by the presence, in the aqueous phase, of potassium nitrosodisulfonate, also referred to as Fremy salt. Matrix Assisted Laser Desorption/Ionization–Time of Flight–Mass Spectrometry (MALDI‐TOF‐MS) was used to determine the influence of electron‐beam irradiation on the chemical stability of surfactants. It was demonstrated that sodium dodecyl benzene sulfonate (SDBS) is not degraded by the irradiation, and is therefore the surfactant of choice for the stabilization of EPM/EPDM‐based latices subjected to electron‐beam irradiation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3600–3615, 2005

Following our previous study on the stereoselective cocrystallization of linear and cyclic dicarboxylic acid residues in copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid (12.6/12.1,4-CHDA, Vanhaecht et al., Macromolecules 2004, 37, 421), we have now investigated a series of copolyamides containing trans or cis isomers of 1,4-diaminocyclohexane (1,4-DACH), viz. 4.14/1,4-DACH.14. Solid-state NMR studies and WAXD experiments demonstrate that the cis isomer is present in the amorphous regions of the copolyamide, whereas the trans isomer is located in both the crystalline and the amorphous phase. Similar to the results for the trans-1,4-CHDA-based copolyamides, trans-1,4-DACH moieties are probably built into the crystalline structure with the cycloaliphatic ring oriented perpendicular to the hydrogen-bonded crystal sheets. Temperature-dependent WAXD patterns show that, unlike in the homopolyamide 4.14, a pseudohexagonal phase is not formed at the Brill temperature in the copolyamide. Instead, crossing rather than merging of the (100) and the combined (010)−(110) WAXD reflections occurs upon heating of the copolyamides containing trans-1,4-DACH. In contrast to the cis isomer, introduction of trans-1,4-DACH into polyamide 4.14 raises the melting temperature, confirming the findings by solid-state NMR and WAXD analysis. Unlike 1,4-CHDA moieties, 1,4-DACH residues do not undergo thermal isomerization. Therefore, at the same amount of initially trans isomers, the copolyamides 4.14/1,4-DACH.14 exhibit higher second heating end melting points than the corresponding isomeric copolyamides 12.6/12.1,4-1,4-CHDA.

The coordination chemistry of various sterically constrained diphosphonites 1−6 with rhodium are reported. The stoichiometric reaction of ligand 5 with [Rh(μ-Cl(CO)2]2 gives rise to the sole formation of trans-[RhCl(CO)(5)] (7), as shown by NMR and IR spectroscopy and X-ray crystallography. The molecular structure reveals a weak interaction between the metal center and the oxygen from the xanthene backbone. This complex serves as a structural model for the first intermediate in the catalytic cycle of rhodium hydroformylation, [Rh(H)(CO)(P&arcraise;P)]. A detailed study on the solution structure of the catalyst resting state under catalytic conditions is performed by high-pressure NMR and FT-IR spectroscopy. The spectroscopic data show that under hydroformylation conditions the bidentate ligands form well-defined complexes with the structure [Rh(H)(CO)2(P&arcraise;P)]. All ligands show preference for a bis-equatorial (ee) coordination mode in the trigonal-bipyramidal Rh complexes. These novel sterically constrained diphosphonite ligands are applied in the rhodium hydroformylation of 1-octene and 2-butene, and good activities and regioselectivities are obtained.

To study the influence of the stereochemistry on the possibility of cocrystallization of linear and cyclic aliphatic residues in copolyamides, a series of copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid with variable compositions were synthesized. From solid-state NMR studies it could be deduced that cis-1,4-CHDA is present in the amorphous regions whereas the trans residues are located in both the crystalline and the amorphous phase. WAXD patterns confirm the presence of trans-1,4-CHDA inside the crystals and reveal that the cycloaliphatic ring is most likely oriented in a direction perpendicular to the crystal sheets that contain the hydrogen bonds. As a result, the intersheet distance is increased compared to that of polyamide 12.6. Furthermore, the rings prevent the genesis of a pseudohexagonal phase above the Brill temperature. Exceptionally, crossing rather than merging of the (100) and the combined (010)−(110) WAXD reflections is observed with increasing temperature, indicating that the intersheet distances increase and become larger than the interchain distances within the hydrogen-bonded sheets before the crystals start to melt. Incorporation of trans-1,4-CHDA residues into polyamide 12.6 leads to higher melting temperatures, pointing at cocrystallization in terms of a solid solution rather than as defects. In contrast, a slight melting point depression is observed for copolymers with predominately cis-1,4-CHDA residues.

Gigantic hollow silica spheres with a hierarchical intra- and inter-particle porosity were obtained from an EO76–PO29–EO76butanolethanolH2O quaternary system, which is unique in its extremely rapid silica condensation and in the resulting hierarchical morphology.

Silicic acid powder was dissolved and polymerized in a concentrated aqueous tetrapropylammonium (TPA) hydroxide solution at room temperature. Two complementary techniques were employed to follow this process leading to silicalite-1 zeolite upon heating. The formation of small silicates and specific oligomers involved in the assembly of silicalite-1 nanoprecursors was investigated using 29Si NMR. Small-angle X-ray scattering (SAXS) was used to follow processes at a colloidal level. Dissolution and polymerization of silicic acid could then be related to events occurring at both molecular and colloidal scales. The appearance of very well-defined colloidal particles was linked to a specific intermediate already observed in systems using an organic and monomeric silica source. In situ time-resolved ultra-small-angle X-ray scattering (USAXS) using synchrotron radiation showed a linear growth of the average crystal diameter, which was slower than of that encountered in Na+ containing synthesis mixtures. Using the results presented here, we propose a mechanism describing the TPA-mediated self-assembly of silicalite-1 from silicic acid powder as silica source. This model is in agreement with rising evidence of a common mechanism involving nanoblock aggregation for organic mediated crystallization of high-silica zeolites.

Silicic acid powder was dissolved and polymerized in a concentrated aqueous tetrapropylammonium TPA hydroxide solution at room temperature. Two complementary techniques were employed to follow this process leading to silicalite-1 zeolite upon heating. The formation of small silicates and specific oligomers involved in the assembly of silicalite-1 nanoprecursors was investigated using 29Si NMR. Small-angle X-ray scattering SAXS was used to follow processes at a colloidal level. Dissolution and polymerization of silicic acid could then be related to events occurring at both molecular and colloidal scales. The appearance of very well-defined colloidal particles was linked to a specific intermediate already observed in systems using an organic and monomeric silica source. In situtime-resolved ultra-small-angle X-ray scattering USAXS using synchrotron radiation showed a linear growth of the average crystal diameter, which was slower than of that encountered in Nacontaining synthesis mixtures. Using the results presented here, we propose a mechanism describing the TPA-mediated self-assembly of silicalite-1 from silicic acid powder as silica source. This model is in agreement with rising evidence of a common mechanism involving nanoblock aggregation for organic mediated crystallization of high-silica zeolites.

Gels of syndiotactic polystyrene with different solvents have been compared to clathrates. Wide-angle X-ray diffraction results using toluene (good solvent for sPS) and decalin (relatively poor solvent for sPS) show that the structure of the crystalline junctions of the gels is similar to that of the clathrate δ-phase. A difference can be found in the width of the (010) reflection, which is, relative to the width of the (&twomacr;10) reflection, much broader for the gel than for the clathrate. This is caused by the difference in mechanism involved for crystal formation in gels and clathrates. Experiments performed on quenched samples of syndiotactic polystyrene with the monomer benzyl methacrylate show that also for this gel the structure of the crystalline part is similar to that of the clathrate phase. This means that solvent is present in both the crystalline and the amorphous part of the gel. By solid-state NMR studies, a clear difference in mobility of solvent molecules in the crystalline and amorphous parts of the gel has been observed.

Microporous amorphous metallosilicates designated as Mg−Si−O and Al−Si−O, with a very narrow pore size distribution around 6 Å diameter, typical surface areas ranging from 350 to 650 m²/g, and loadings of well-dispersed metal oxide (up to about 10 wt % metal) result from the controlled calcination of magnesium and aluminum silsesquioxane complexes [(c-C5H9)7Si7O12]2Mg4Cl2·2THF, 1, {[(c-C5H9)7Si7O12]Al}n, 2, and [(c-C5H9)7Si7O11(OSiMe3)]Al[(c-C5H9)7Si7O10(OSiMe3)(OH)], 3. Moreover, textural properties such as surface area and pore volume can be easily adjusted by varying the calcination conditions, while the pore size distribution remains practically unchanged. XPS, EDX, solid-state MAS ²⁹Si and ²⁷Al NMR, and HRTEM measurements suggest that the metal is present in M−Si−O materials mainly as isolated metal ions incorporated in the amorphous silica framework and also as small crystalline metal oxide particles of a few nanometers, which are well dispersed throughout the silica. SEM was employed as well to evaluate particle size and morphology. IR spectroscopy of adsorbed acetonitrile showed that both Al−Si−O materials are strong Lewis acids. Mg−Si−O and Al−Si−O were briefly tested as catalysts in 1-butanol dehydration. Mg−Si−O gave both dehydrogenation and dehydration, while on Al−Si−O only dehydration and cracking reactions occurred.

Using 1D- and 2D-exchange ¹³C NMR techniques it is shown that n-pentane translation in zeolite ZK-5 occurs by hopping between neighboring α and γ cages. Owing to the structure of the ZK-5 pore network, these techniques give direct information about the translational part of molecular intercage motion, which represents the elementary step of sorbate self-diffusion. Between 247 and 317 K the hopping rates obtained for n-pentane in H- and K-ZK-5 at respective loadings of 8.1 and 9.9 molecules per unit cell are of the order of 1–10³ s⁻¹. This corresponds to intra-zeolite self-diffusion constants of 10⁻¹⁸–10⁻¹⁵ m² s⁻¹. Non-exponential time-correlation functions indicate heterogeneity, possibly reflecting the different loading states of the individual cages at the microscopic level. The temperature dependence of hopping shows that it is an activated process with a barrier of 28 ± 5, kJ mol⁻¹ for both H-ZK-5 and K-ZK-5. The apparent activation entropy determined from a two-site exchange analysis is 130 ± 20 J K⁻¹ mol⁻¹ for both H- and K-ZK-5. Copyright © 1999 John Wiley & Sons, Ltd.

Telechelic oligo- and poly(dimethylsiloxanes) 1 and 2, with two ureidopyrimidone (UPy) functional groups, have been prepared via a hydrosilylation reaction. The compounds have been characterized in solution by ¹H NMR and viscometry and in the solid state by ¹H NMR and ¹³C NMR, FTIR, and rheology measurements. The measurements show that the UPy groups of 1 and 2 are associated via quadruple hydrogen bonds in a donor−donor−acceptor−acceptor (DDAA) array. In many aspects, the materials behave like entangled, high molecular weight polymers. Compound 2 has a Tg at −119 °C and shows melting of microcrystalline domains of associated UPy units at −25 °C. Compound 1 has a crystalline form (Tm = 112 °C) and an amorphous modification with a Tg of 25 °C. Solid-state NMR was used to investigate the mobility of these phases. WISE spectra show a higher mobility of the UPy groups in the amorphous phase than in the crystals of 1. Amorphous 1 and 2 behave like entangled polymers. Their mechanical behavior is characterized by a rubbery plateau and a relatively high activation enthalpy for stress relaxation (ΔH = 127 kJ/mol for 1; ΔH = 54 kJ/mol for 2), which was derived from the temperature dependence of the zero-shear viscosity. Estimates for the degree of polymerization (DP) of 1 and 2, based on the mechanical properties, give DP > 100 for 1 and approximately 20 for 2. Like in condensation polymerization, the DP's of reversible supramolecular polymers are presumably limited by the presence of small amounts of monofunctional impurities.

Various metal-substituted ammonium gallophosphates (metal is Zn, Mn, Mg, and Fe) have been synthesized. Characterization by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and ³¹P MAS and ⁷¹Ga MAS NMR shows that the structures are similar and isostructural to the known ammonium cobalt gallophosphate hydrate, [NH4][CoGa2P3O12(H2O)2]. It is concluded from a combined in situ XRD/XAS study that the gallophosphate molecular sieves described here are not thermally stable and lose their microporous nature above 350 °C.