Christian Detellier

The incorporation of acetone molecules inside the tunnels of sepiolite (SepSp-1) was monitored by a variety of techniques. By exposing sepiolite previously dehydrated at 120 °C for 20 h to acetone vapor at room temperature, acetone molecules incorporate into the tunnels of sepiolite in the minute timescale, form H-bonds with structural water, and restore the original structure of sepiolite. The characteristic signals of the ²⁹Si CP/MAS NMR spectrum of sepiolite are almost completely recovered in less than a minute. The TGA-DTA-MS results show that a large mass loss appears at 130 °C and a new mass loss appear at 380 °C for sepiolite previously heated at 120 °C for 20 h then exposed to acetone for a month. The mass loss at 130 °C is mainly accounted for by the release of structural water and a portion of the incorporated acetone. The mass loss at 380 °C is due to the release of the residue of acetone molecules that coordinate directly to terminal Mg(II) cations in the tunnels. The incorporation of acetone molecules inside the tunnels of sepiolite and its modifications upon thermal treatment were also studied by textural analysis, and ²⁹Si and ¹³C solid-state NMR techniques. A nanohybrid material with a structure similar to the parent sepiolite, is formed through the direct coordination of acetone molecules to the terminal Mg(II) cationic coordination. The coordinated acetone molecules stabilize the tunnel structure which collapses at a temperature much higher than in the case of the sepiolite mineral.

A novel class of organic–inorganic nanohybrid material was prepared by the intercalation in kaolinite of a molten organic salt (1-ethyl pyridinium chloride, EP) above its melting temperature. The intercalation proceeded at 170 °C under N₂. It did not succeed when kaolinite was used as the starting material, whereas the melt intercalation process was possible when DMSO–kaolinite (DMSO-K) was used as the starting material. The amount of EP loaded in the galleries of kaolinite is 24.3% (0.574 mol of EP per unit-cell) which produces an increase of the basal spacing d₀₀₁ from 1.10 nm in the case of DMSO-K to 1.35 nm. The melt intercalation process could be dramatically improved by the choice of the temperature of reaction as well as of the atmosphere. At lower temperatures (less than 140 °C), even if the reaction medium is the ionic liquid, the intercalation is not observed. This results from the non-release of DMSO from the interlamellar space of DMSO-K, a step essential for the intercalation of EP to proceed. This work indicates that the intercalation of EP and the displacement of DMSO from the interlamellar spaces of kaolinite take place concurrently, not in a sequential manner. However, the process is initially driven by the thermal removal of DMSO.

The reorientational dynamics of p‐sulfonatocalix[4]arene and of its La(III) complex in deuterated water were studied by ¹H NMR longitudinal relaxation rates. It is shown that the relaxation is purely dipolar in the non‐extreme narrowing regime. The distance between the geminal protons could be determined from the NMR data, giving good agreement with the values generally used in correlation time calculations. The correlation times show an Arrhenius behaviour in good agreement with previously reported data from ¹³C measurements for a similar uncomplexed calixarene. The Arrhenius energies of activation are identical for the uncomplexed and the complexed calixarenes, suggesting a reorientational motion strongly dependent on the structure of the water cage around the complex. This is also in agreement with a complexation of the La(III) cation in the second sphere of solvation of the sulfonate groups, as shown by molecular dynamics simulations. Copyright © 2004 John Wiley & Sons, Ltd.

The kinetics of the ring inversion of p-sulfonatocalix[4]arene and of its La(III) and Ca(II) 1 ∶ 1 complexes have been studied by ¹H NMR in D₂O and in a binary mixture 50 ∶ 50% w/w D₂O ∶ (CD₃)₂CO. The exchange between the axial and the equatorial methylene protons was followed. The ring inversion is slowed down in the binary mixture, and in the presence of Ca(II) and La(III) with a larger effect in the latter case. The results of this study are in agreement with a coordination of the sulfonate groups to the second sphere of coordination of the cations. The effect of the solvent and of the cations on the ring inversion rates is purely entropic, with entropies of activation ranging from 2 to 51 J K⁻¹ mol⁻¹, while the enthalpies of activation are constant in the limits of experimental errors, around 60 kJ mol⁻¹. It is proposed that the entropy control of the ring inversion results from the breaking of the structure of the water molecules forming the solvent cage around the calixarene.

The complexation of the caesium cation by a p-tert-butylcalix[6]arene hexaacetamide derivative (5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40-hexakis(N,N-diaethylaminocarbonyl)methoxycalix[6]arene) (I) in a binary mixture of deuterated chloroform and acetonitrile was studied by ¹H, ¹³³Cs NMR spectroscopy and X-ray crystallography. Different complexes between Cs⁺ and I with Cs⁺ ∶ I stoichiometries ranging from 1 to 3 are formed in solution. The 3 ∶ 1 complex is only observed below 250 K, in the presence of excess of Cs⁺. The structure of the 2 ∶ 1 complex in solution is similar to the distorted partial cone crystal structure in the solid state. The two caesium cations are coordinated to carbonyl and phenolic oxygens, with a short distance of 4.16 Å between them. The dissociation of the 2 ∶ 1 complex follows a dissociative mechanism with ΔH^≠ = 58 kJ mol⁻¹ and ΔS^≠ = −2 J K⁻¹ mol⁻¹. The activation parameters indicate that the dissociative process is kinetically governed by the successive flipping of two aromatic rings leading to a 1,2,3 alternate conformation of a 1 ∶ 1 complex, similar to the crystal structure of the uncomplexed calix[6]arene hexaacetamide.

This paper reports the intercalation of alditols into the interlamellar spaces of kaolinite. The alditols were adonitol, a meso compound, and D-sorbitol. The grafting of hydroxy groups onto the aluminol internal surfaces of kaolinite followed the intercalation. The polyols were intercalated into kaolinite by displacing dimethyl sulfoxide (DMSO) from the DMSO–kaolinite intercalate (Kao–DMSO). This was done directly from the alditol melt at temperatures just above the melting point of the respective polyols. The intercalated polyols are arranged in a flattened monolayer arrangement, such that the interlayer expansion was 3.1 Å (adonitol) and 4.6 Å ( D-sorbitol). Infrared spectroscopy showed that heating the intercalated materials at 200 °C for 1 h resulted in the grafting of the alditols on the inner aluminol surface of kaolinite. ¹³C CP and DD/MAS NMR indicated the complete replacement of the DMSO molecules by the alditol guests and that the alditols were rigidly constrained in the interlamellar spaces of kaolinite. The intercalation of adonitol was monitored with time. The reaction proceeds via a partial collapse of the Kao–DMSO intercalate before the intercalation of the adonitol.

The compound 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(N,N-diethylaminocarbonyl)methoxycalix[4]arene, 1, forms a 1 ∶ 1 complex with the sodium cation in a binary 1 ∶ 1 solution of chloroform-d and acetonitrile-d₃ with tetraphenylborate as the counteranion. Kinetic and mechanistic solution studies were analyzed using ¹H and ²³Na NMR. The formation of a 1 ∶ 1 complex of 1 with the sodium cation is quantitative (K_f > 10⁴ M⁻¹) at 238, 274, and 320 K. The exchange between complexed and solvated sodium cation is very slow on the ²³Na NMR time scale even at 320 K. Analysis of 2D EXSY ¹H NMR data for the interconversion of the methylene protons from the N(CH₂CH₃)₂ moiety of the (Na,1)⁺ complex shows slow exchange at 320 K. The complexes (Na,1,MeCN),(Na,1),(BPh₄)₂ and (MeCN,1) were crystallographically characterized. X-Ray crystallographic data of (Na,1,MeCN),(Na,1),(BPh₄)₂ confirm the NMR data such that the sodium cation is encapsulated by the hydrophilic pseudo-cavity of 1. The crystal structure shows two diastereomorphs of (Na,1)⁺ in the lattice differing by a twist in the OCH₂CO arms and only one diastereomorph contains a second guest, acetonitrile, in the hydrophobic pseudo-cavity of 1. The crystal structure of (MeCN,1) shows identical preorganization of the hydrophobic pseudo-cavity to the complex (Na,1)⁺.

Layered double hydroxides (LDH) containing NiAl or NiV of varying M(II) ∶ M(III) ratios have been prepared by coprecipitation and characterized by XRD, elemental analysis, and FT-IR. The LDHs electrochemical properties were investigated to determine their potential application as positive electrodes in Ni–Cd and NiMH batteries. Analysis of the electrochemical behavior of the LDHs indicates that the performance is not only dependant on the M(II) ∶ M(III) ratios but also on the degree of structural disorder of the material. The well-crystallized Ni₅Al LDH exchanges up to 1.5 electrons in early cycles but is not stable and collapses on oxidative charging to the oxyhydroxide form. The turbostratic Ni₂Al LDH exchanges more electrons (up to 1.6) and is more stable during charging. However, owing to a lower density in comparison to Ni₅Al, it has a poorer loading capacity. The NiV LDHs exchange a maximum of 1.1 electrons due to the high stability of the higher oxidation states of vanadium, and thus are poor candidates for rechargeable materials.