Boronate Ligands in Materials: Determining Their Local Environment by Using a Combination of IR/Solid‐State NMR Spectroscopies and DFT Calculations

Boronic acids (R‐B(OH)₂) are a family of molecules that have found a large number of applications in materials science. In contrast, boronate anions (R‐B(OH)₃^?) have hardly been used so far for the preparation of novel materials. Here, a new crystalline phase involving a boronate ligand is described, Ca[C₄H₉‐B(OH)₃]₂, which is then used as a basis for the establishment of the spectroscopic signatures of boronates in the solid state. The phase was characterized by IR and multinuclear solid‐state NMR spectroscopy (¹H, ¹³C, ¹¹B and ⁴³Ca), and then modeled by periodic DFT calculations. Anharmonic OH vibration frequencies were calculated as well as NMR parameters (by using the Gauge Including Projector Augmented Wave—GIPAW—method). These data allow relationships between the geometry around the OH groups in boronates and the IR and ¹H NMR spectroscopic data to be established, which will be key to the future interpretation of the spectra of more complex organic–inorganic materials containing boronate building blocks.     

Formation of a Single-Crystal Aluminum-Based MOF Nanowire with Graphene Oxide Nanoscrolls as Structure-Directing Agents

An innovative strategy is proposed to synthesize single-crystal nanowires (NWs) of the Al³⁺ dicarboxylate MIL-69(Al) MOF by using graphene oxide nanoscrolls as structure-directing agents. MIL-69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM-HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL-69(Al) NWs involving size-confinement and templating effects. The formation of MIL-69(Al) seeds and the self-scroll of GO sheets followed by the anisotropic growth of MIL-69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures.     

Some remarks on the ionic conductivity in NaY dehydrated zeolite

On the basis of experimental measurements of the electrical conductivity of the Nafaujasite zeolites (NaY), treated under vacuum up to 673 K for 24 hours, we clearly demonstrate that the behavior of the measured conductivity σ_ac of the dehydrated zeolite NaY, over an interval of high frequency change, may be described by a power-law function: σ_ac=A▹^s. The exponent s, in this case, should be considered as temperature and frequency dependent when the parameter A is a temperature dependent function. On the other hand, when considering the measured conductivity as a sum of two terms (σ_ac=σ₀+σ′(▹)) resulting from the contributions of the dc and the ac components respectively, we find that one of them obeys the Arrhenius law while the other can be expressed as A▹^s. Parameter s is practically frequency independent when the frequency of the applied electrical field is higher than a characteristic value ▹_c A comparison with the measurements performed on NaY dehydrated at 435 K is also included. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995     

“In-situ” monitoring activation and reaction on very absorbing catalytic solid by DRIFT spectrometer

The FTIR's well-known advantages are strongly shown by the use of new infrared techniques. Both advantages of FTIR and diffuse reflectance make this coupling particularly important in the development of infrared studies.Sensitivity and rapidity of the FTIR spectrometer, added to the extremely simple preparation of the sample, allowed by diffuse reflectance attachment, give a high performing tool particularly in catalysis in the view of understanding the catalytic reactions mechanisms. We have chosen thein-situ study of two catalytic systems active in selective hydrogénation of dienes: a copper-chromium oxide and Cu/Al₂O₃ .     

Process of polarization and analysis of the water adsorption on a zeolite

We report the study of the dielectric relaxation mechanisms in the zeolite Na-X, “Faujasite”, by means of the method of Thermally Stimulated Depolarization Currents (TSDC), and polarization conductivity versus frequency. We give particular interest to the effect of adsorption on the evolution of dielectric parameters. Two distinct relaxation processes attributed to adsorbed water were found by TSDC measurements. Moreover, the polarization conductivity gives two sets of values of the potential barrier height. The evolution of the polarization conductivity as a function of the rate p/p° is comparable to the curve showing the isothermal water adsorption. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Electrospray ionization mass spectrometry: a key analytical tool for the characterization of regioselectively derivatized maltooligosaccharides obtained starting from natural beta-cyclodextrin

The development of natural cyclodextrins (CDs) for various industrial applications (agroalimentary, cosmetic or pharmaceutical) constitutes a continuous challenge. For the integration of these agricultural plant products in the creation of super-absorbent biodegradable and hypoallergenic materials (water-retaining agents, cosmetic hydrating and texturing, pharmaceutical and horticultural products) to replace synthetic polymers, we have developed chemical methods to access regioselectively C-6-derivatized maltooligosaccharides starting from CDs. These compounds are highly suitable for further chemical modifications and are expected to give access to a new class of polymeric materials with potential applications such as water-retaining agents in the disposable nappies industry. For the structural analysis of carbohydrates, electrospray ionization mass spectrometry (ESI-MS) offers precise results, analytical versatility and very high sensitivity. We report herein the rapid and convenient follow-up of chemical reactions, the purity evaluation of intermediates and final products, and the structural characterization of derivatized maltooligosaccharides, obtained by acidic cleavage (acetolysis) of halogenated and esterified CDs, using ESI-MS in combination with the high-resolution (HRMS) and tandem mass spectrometry (MS/MS) capabilities of a quadrupole orthogonal time-of-flight (Q-TOF) mass spectrometer.     

Potentiometric determination of potassium cations using a nickel(II) hexacyanoferrate-modified electrode

Electroactive nickel(II) hexacyanoferrate (NiHCF) thin film modified electrodes are effective potentiometric sensors for the determination of potassium ions. The NiHCF films are deposited onto glassy carbon electrodes by repetitive potential cycling in K(3)Fe(CN)(6)/NaNO(3)/Ni(NO(3))(2) solution. The modified electrodes exhibit a linear response to potassium ions in the concentration range 1x10(-3) to 2.0 mol dm(-3), with a near-Nernstian slope (45-49 mV per decade) at 25 degrees C. In the determination of potassium ion in syrups used for treatment of potassium deficiency, the NiHCF-modified electrode gave comparable results to those obtained using flame emission spectrophotometry.     

The missing mass squared dependence of the average charged particle multiplicity in the reaction K+p → KoX++ from 5–16 GeV/c

The average charged particle multiplicity, 〈n_ch(M_X²)〉, in the reaction K⁺p→K^oX⁺⁺ is studied as a function of the mass squared, M_X², of the recoil system X and also as a function of the K^o transverse momentum, p_T, at incident momenta of 5.0, 8.2 and 16.0 GeV/c. The complete data samples yield distributions which are not independent of c.m. energy squared, s, They exhibit a linear dependence on log (M_X²_X/M_o²)[M_o²=1 GeV²] with a change in slope occurring for M_X²≈s/2, and do not agree with the corresponding distributions of 〈n_ch〉 as a function of s for K⁺ p inelastic scattering. Sub-samples of the data for which K^o production via beam fragmentation, central production and target fragmentation are expected to be the dominant mechanisms show that, within error, the distribution of 〈n_ch(M_X²)〉 versus M_X² is independent of incident momentum for each sub-sample separately. In particular in the beam fragmentation region the 〈n_ch(M_X²)〉 versus M_X² distribution agrees rather well with that of 〈n_ch〉 versus s for inelastic K⁺p interactions. The latter result agrees with recent results on the reactions pp → pX and π^?p → pX in the NAL energy range. Evidence is presented for the presence of different production mechanisms in these separate regions.