Aluminum aminoterephthalate Al(OH)[H(2)N-BDC] x 0.3 (H(2)N-H(2)BDC (denoted MIL-53-NH(2)(as)) was synthesized under hydrothermal conditions. The activation of the compound can be achieved in two steps. The treatment with DMF at 150 degrees C leads to Al(OH)[H(2)N-BDC] x 0.95 DMF (MIL-53-NH(2)(DMF)). In the second step, DMF is thermally removed at 130 degrees C. Upon cooling in air, the hydrated form Al(OH)[H(2)N-BDC] x 0.9 H(2)O (MIL-53-NH(2)(lt)) is obtained. The dehydration leads to a porous compound that exhibits hysteresis behavior in the N(2) sorption experiments. The MIL-53-NH(2)(lt) can be modified by postsynthetic functionalization using formic acid, and the corresponding amide Al(OH)[HC(O)N(H)-BDC] x H(2)O (MIL-53-NHCHO) is formed. All four phases were thoroughly characterized by X-ray powder diffraction, solid-state NMR and IR spectroscopy, and sorption measurements, as well as thermogravimetric and elemental analysis. Based on the refined lattice parameter similar breathing behavior of the framework as found in the unfunctionalized MIL-53 can be deduced. Solid-state NMR spectra unequivocally demonstrate the presence of the guest species, as well as the successful postsynthetic functionalization.

Applying a combination of melt synthesis followed by long-term annealing a fluorohectorite is obtained which is unique with respect to homogeneity, purity, and particle size. Counterintuitively, the hectorite undergoes a disorder-to-order transition upon swelling to the level of the bilayer hydrate. Alkylammonium-exchanged samples show at any chain length only a single basal spacing corroborating a nicely homogeneous layer charge density. Its intracrystalline reactivity improves greatly upon annealing, making it capable to spontaneously and completely disintegrate into single clay lamellae of 1 nm thickness. Realizing exceptional aspect ratios of around 20,000 upon delamination, this synthetic clay will offer unprecedented potential as functional filler in highly transparent nanocomposites with superior gas barrier and mechanical properties.

All μ-hydroxyl groups are frequently encountered capping groups found on the external surfaces of various minerals that are often used as fillers in composite materials. Covalent grafting to this functional group would therefore offer a versatile and attractive route to surface modification. The octahedral layer of kaolinite is composed of μ-bridged aluminol groups. In particular, intercalation compounds of kaolinite, where all basal planes are exposed and may be modified, are ideally suited to study the feasibility of such covalent graftings. The huge (internal) specific surface area greatly improves the sensitivity of the analytics and renders kaolinite an ideal model compound. Herein we analyze the mode of bonding of ethylene glycol (EG), intercalated into kaolinite (EG kaolinite), by solid-state NMR techniques. 27 Al MQMAS allows for distinction between intercalated and grafted EG molecules because the chemical surroundings of octahedrally coordinated aluminum nuclei in the layer are significantly changed by the formation of a covalent bond. Moreover, the temperature-dependent dynamics of the EG molecules in the interlamellar space are examined by wide-line solid-state 1 H NMR measurements. The EG molecules perform a circular motion around the covalently bonded hydroxyl group in the interlamellar space. Analysis of the 13 CÀ 27 Al REAPDOR measurement in conjunction with the EG dynamics allows for determination of the 13 C 3 3 3 27 Al distance between octahedral aluminum and the bonded carbon atom of EG. This distance is 3.1 Å. A thorough description of the bonding mode of the EG molecules is provided and proves beyond any doubt the covalent grafting. This suggests that the reactivity of μ-hydroxyl groups, in general, is sufficient to realize a covalent surface modification of a wide range of minerals.

Using a synthetic Na-fluorohectorite ([Na 0.5 ] inter [Mg 2.5 Li 0.5 ] oct [Si 4 ] tet O 10 F 2 ), mixed-cation heterostructures with an alternating interstratification pattern are formed under appropriate conditions via simple cation-exchange reactions. The most important requirement for the spontaneous formation of these ordered mixed-layer structures is a high degree of charge homogeneity of the smectite. The partial exchange of cations with largely different hydration enthalpies (Na þ by K þ ) results in the regular interstratification of hydrated (d = 12.4 A ˚) and nonhydrated (d = 10.0 A ˚) interlayers at 40% relative humidity (RH). By combining analytical methods that are sensitive to either hydrated or collapsed interlayers (selective cation exchange, hydrosorption isotherms, and 23 Na MAS NMR spectroscopy), we proposed a novel mechanism that is centered at the interlayers and does not require polar lamellae, as suggested in the literature for rectorite formation. Upon formation of the regular interstratification, the charge density of the interlayers changes from homogeneous to alternating between interlayers in the stacking direction. This simple redistribution of exchangeable interlayer cations is facile and rapid. The cation exchange capacity (CEC) of the collapsed interlayers is higher than the average CEC, while the CEC of the hydrated interlayers will be correspondingly lower. The local CEC of these interlayers deviates by ∼18%-28% from the average CEC, as calculated independently from ion-exchange experiments and hydrosorption measurements. Moreover, this alternating differentiation of the interlayer cation concentration seems to be driven by thermodynamics. Even a mixture of homocationic Na-hectorite and K-hectorite slowly converts to a regularly interstratified material when immersed in water. After the interlayers are differentiated, they may be selectively manipulated, creating dual functional materials, where distinct nanoreactors are separated by a 1-nm-thick insulating lamellae and are arranged in a regular manner.

Kaolinite platelets have inherent Janus character owing to a polar crystal structure. This character is, however, ineffective without selective modification of the two hydrophilic external basal surfaces. Amplification of the difference in the chemical nature of the surfaces is achieved by cation exchange on one side and by covalent grafting on the other. After adjustment of the surface tension, kaolinite is an effective emulsifier.