Radical Grafting of Tetrafluoroethylene and Vinylidene Fluoride Telomers onto Silica Bearing Vinyl Groups

Radical addition of ω-iodofluorinated telomers was used to modify silica (S50) nanoparticles bearing vinyl groups. These iodo terminated derivatives were either commercially available tetrafluoroethylene telomers, CnF2n+1I with n = 4 or 6, or vinylidene fluoride telomers, CnF2n+1[VDF]mI with m = 6 and 23. These latters were synthesized by radical telomerization of VDF with CnF2n+1I initiated by bis(4-tert-butylcyclohexyl) peroxydicarbonate in high yields (>85%). The resulting nanohybrids were characterized by solid state NMR spectroscopy, elemental analyses and thermogravimetry. A covalent grafting between double bonds and fluorinated iodotelomers was noted. The covering density of fluorinated chains was assessed and reported with respect to fluorinated chain lengths. These nanohybrids exhibited a high thermostability (higher than 400 °C under air), losing less than 10% by weight at 700 °C, and a low surface tension, γs, from around 15 mN·m–1 to about 44 mN·m–1 for silica

¹⁴N: A Sensitive NMR Probe for the Study of Surfactant–Oxide Interfaces

We explored the sensitivity of the 14N quadrupolar interaction toward the characterization of surfactant–oxide interfaces. For the first time, experimental 14N NMR spectra are recorded, modeled, and compared for three different mesostructured silica (hexagonal p6mm, cubic Ia3d, and lamellar) templated by hexadecyltrimethylammonium cations (CTA+). Broad distributions in quadrupolar coupling constant CQ are obtained showing differences between phases. In parallel, quantum chemical calculations using the Born–Oppenheimer molecular dynamics in combination with DFT have been successfully undertaken in a time scale of 25–32 ps to better understand the experimental results. From the two simulated models (CTA+ alone vs CTA+ in interaction with a D4R– silicate oligomer), we evidenced the relative effect of fast conformational variations and of intermolecular interactions on the time-averaged 14N quadrupolar parameters. 14N relaxation and 13C CSA NMR data are also briefly presented and discussed. Our approach opens new directions for studying a wide range of mesostructured materials

¹⁴N and ⁸¹Br Quadrupolar Nuclei as Sensitive NMR Probes of <i>n</i>-Alkyltrimethylammonium Bromide Crystal Structures. An Experimental and Theoretical Study

This is the first time a comprehensive study has been carried out on n-alkyltrimethylammonium bromide salts using 14N and 81Br solid state NMR, X-ray diffraction, and theoretical calculations. The investigation represents a necessary step toward further 14N and 81Br NMR characterization of the environment of cationic and anionic groups in materials, accounting for the amphiphilic properties of cationic surfactants. The NMR spectra of five CxH2x+1(CH3)3N+Br− polycrystalline samples with different n-alkyl chain lengths (x = 1, 12, 14, 16, 18) were recorded and modeled. The 14N and 81Br quadrupolar coupling interaction parameters (CQ, ηQ) were also estimated from spectrum modeling and from computer simulation. The obtained results were discussed in depth making use of the experimental and reoptimized crystal structures. In the study, both 14N and 81Br nuclei were found to be sensitive probes for small structural variations. The parameters which influence the NMR properties the most are mobility, deviation of C−N−C bond angles from Td angles, and variations in r(N−Br) distances

Ionic Liquid Mediated Sol-Gel Synthesis in the Presence of Water or Formic Acid: Which Synthesis for Which Material?

Sol-gel syntheses involving either neutral water or formic acid as a reactant have been investigated (1) to determine the best conditions to confine a maximum of ionic liquid (IL) inside silica-based matrixes and (2) to reach the highest porosity after removing the IL from the ion gels (washed gels). Several sets of ionogels were prepared from various 1-butyl-3-methylimidazolium ILs and various silica or organosilica sources. The study evidenced a critical effect of the anion on the morphology (monolith, powder) and texture of the resulting washed gels. Particularly, tetrafluoroborate anion led to monolith ionogels by a simple hydrolytic method, affording highly condensed mesoporous silicas with some fluorinated surface sites. Such sites have never been reported before and were evidenced by ¹⁹F NMR. On the other hand, formic acid solvolysis turned out to be the only method to get non-exuding, crack-free, and transparent monoliths from ILs containing bis­(trifluoromethylsulfonyl)­imide [NTf₂] anion, with promising applications in photochemistry or photosensing. With bulky imidazolium and pyridinium cations, removal of the IL led to highly porous silicas with pore diameters and pore volumes as high as 10–15 nm and 3 cm³ g^–1, respectively. These silicas could find applications as supports for immobilizing bulky molecules

Hybrid Materials and Periodic Mesoporous Organosilicas Containing Covalently Bonded Organic Anion and Cation Featuring MCM-41 and SBA-15 Structure

We report the synthesis of a new trialkoxysilylated ionic liquid based on disilylated guanidinium and monosilylated sulfonimide species. This compound allowed the successful preparation of new periodic mesoporous organosilicas containing covalently anchored ion-pair through both organo-cationic and organo-anionic moieties which have never been reported up to now. Two classes of hybrid materials containing guanidinium−sulfonimide ion-pairs (IPs) have been synthesized. The first type of material was prepared by grafting the silylated IP onto both MCM-41-type and SBA-15-type silicas according to a surface sol−gel polymerization. The second class was synthesized following a one-pot sol−gel procedure using silylated IP and tetraethoxysilane as framework precursors. These latter materials correspond to so-called periodic mesoporous organosilicas (PMOs) and gave “organo-ionically” modified MCM-41 and SBA-15 related solids. The materials were characterized by a series of techniques including XRD, nitrogen sorption, solid-state NMR, FTIR, transmission electronic microscopy, and elemental analysis. The highest structural regularity in terms of pore size distribution and channel size homogeneity was observed for IP-PMOs possessing SBA-15-type architecture due to an enhanced trialkoxysilylated IP precursor/surfactant interaction. Solvatochromic experiments with Reichardt’s dye showed good accessibility of the silica-supported ion-pair and suggested the formation of monophasic materials

Host–Guest Silicalite‑1 Zeolites: Correlated Disorder and Phase Transition Inhibition by a Small Guest Modification

We have investigated the nature and extent of nanoscale disorder in prototypical host–guest zeolites, made of silicalite-1 (host) and organic structure-directing agent (OSDA, guest). The four different selected OSDA-silicalite-1 differ in: the mineralizing agent used (F– vs OH–), the synthesis method (hydrothermal vs solvent-free), and the OSDA (tetrapropylammonium (TPA) vs tripropylethylammonium TPEA). The comparison between TPA and TPEA, chemically similar but differing in their symmetry, is examined in great detail owing to the novel relationship found between the geometrical disorder and the monoclinic–orthorhombic (m–o) phase transition occurring at low temperatures. Long- and short-range organization and ordering are characterized by complementary X-ray diffraction (XRD), Raman analysis, and multinuclear NMR spectroscopy (13C, 14N, 29Si). The possibility of the m–o transition is studied by all of these techniques at variable low T values. An in-depth study of the disorder is carried out by X-ray structure determination and two-dimensional (2D) NMR 29Si–29Si INADEQUATE correlations, including an up-to-date analysis of anisotropic atomic displacement parameters and a new fitting approach to estimate correlated disorder from 2D NMR data sets. The collected results allow us to demonstrate how the disorder created by the positioning of the less symmetric TPEA guest leads to a correlated geometrical disorder for half of the atom sites in the host framework that completely inhibits the m–o phase transition

Synthesis and Characterization of Crystalline Structures Based on Phenylboronate Ligands Bound to Alkaline Earth Cations

We describe the preparation of the first crystalline compounds based on arylboronate ligands PhB(OH)3– coordinated to metal cations: [Ca(PhB(OH)3)2], [Sr(PhB(OH)3)2]·H2O, and [Ba(PhB(OH)3)2]. The calcium and strontium structures were solved using powder and single-crystal X-ray diffraction, respectively. In both cases, the structures are composed of chains of cations connected through phenylboronate ligands, which interact one with each other to form a 2D lamellar structure. The temperature and pH conditions necessary for the formation of phase-pure compounds were investigated: changes in temperature were found to mainly affect the morphology of the crystallites, whereas strong variations in pH were found to affect the formation of pure phases. All three compounds were characterized using a wide range of analytical techniques (TGA, IR, Raman, XRD, and high resolution 1H, 11B, and 13C solid-state NMR), and the different coordination modes of phenylboronate ligands were analyzed. Two different kinds of hydroxyl groups were identified in the structures: those involved in hydrogen bonds, and those that are effectively “free” and not involved in hydrogen bonds of any significant strength. To position precisely the OH protons within the structures, an NMR-crystallography approach was used: the comparison of experimental and calculated NMR parameters (determined using the Gauge Including Projector Augmented Wave method, GIPAW) allowed the most accurate positions to be identified. In the case of the calcium compound, it was found that it is the 43Ca NMR data that are critical to help identify the best model of the structure

Synthesis and Characterization of Crystalline Structures Based on Phenylboronate Ligands Bound to Alkaline Earth Cations

We describe the preparation of the first crystalline compounds based on arylboronate ligands PhB(OH)3– coordinated to metal cations: [Ca(PhB(OH)3)2], [Sr(PhB(OH)3)2]·H2O, and [Ba(PhB(OH)3)2]. The calcium and strontium structures were solved using powder and single-crystal X-ray diffraction, respectively. In both cases, the structures are composed of chains of cations connected through phenylboronate ligands, which interact one with each other to form a 2D lamellar structure. The temperature and pH conditions necessary for the formation of phase-pure compounds were investigated: changes in temperature were found to mainly affect the morphology of the crystallites, whereas strong variations in pH were found to affect the formation of pure phases. All three compounds were characterized using a wide range of analytical techniques (TGA, IR, Raman, XRD, and high resolution 1H, 11B, and 13C solid-state NMR), and the different coordination modes of phenylboronate ligands were analyzed. Two different kinds of hydroxyl groups were identified in the structures: those involved in hydrogen bonds, and those that are effectively “free” and not involved in hydrogen bonds of any significant strength. To position precisely the OH protons within the structures, an NMR-crystallography approach was used: the comparison of experimental and calculated NMR parameters (determined using the Gauge Including Projector Augmented Wave method, GIPAW) allowed the most accurate positions to be identified. In the case of the calcium compound, it was found that it is the 43Ca NMR data that are critical to help identify the best model of the structure