The synthesis, characterization, and proposed mechanism of formation of a new family of silicatelaluminosilicate mesoporous molecular sieves designated as M41S is described. MCM-41, one member of this family, exhibits a hexagonal arrangement of uniform mesopores whose dimensions may be engineered in the range of - 15 A to greater than 100 A. Other members of this family, including a material exhibiting cubic symmetry, have ken synthesized. The larger pore M41S materials typically have surface areas above 700 m2/g and hydrocarbon sorption capacities of 0.7 cc/g and greater. A templating mechanism (liquid crystal templating-LCT) in which surfactant liquid crystal structures serve as organic templates is proposed for the formation of these materials. In support of this templating mechanism, it was demonstrated that the structure and pore dimensions of MCM-41 materials are intimately linked to the properties of the surfactant, including surfactant chain length and solution chemistry. The presence of variable pore size MCM-41, cubic material, and other phases indicates that M41S is an extensive family of materials.

http://dns2.asia.edu.tw/~ysho/ysho-english/1000 wc/pdf/j ame che soc114, 10834.pdf

A new family of mesoporous molecular sieves prepared with liquid crystal templates

Organic–inorganic hybrid materials do not represent only a creative alternative to design new materials and compounds for academic research, but their improved or unusual features allow the development of innovative industrial applications. Nowadays, most of the hybrid materials that have already entered the market are synthesised and processed by using conventional soft chemistry based routes developed in the eighties. These processes are based on: a) the copolymerisation of functional organosilanes, macromonomers, and metal alkoxides, b) the encapsulation of organic components within sol–gel derived silica or metallic oxides, c) the organic functionalisation of nanofillers, nanoclays or other compounds with lamellar structures, etc. The chemical strategies (self-assembly, nanobuilding block approaches, hybrid MOF (Metal Organic Frameworks), integrative synthesis, coupled processes, bio-inspired strategies, etc.) offered nowadays by academic research allow, through an intelligent tuned coding, the development of a new vectorial chemistry, able to direct the assembling of a large variety of structurally well defined nano-objects into complex hybrid architectures hierarchically organised in terms of structure and functions. Looking to the future, there is no doubt that these new generations of hybrid materials, born from the very fruitful activities in this research field, will open a land of promising applications in many areas: optics, electronics, ionics, mechanics, energy, environment, biology, medicine for example as membranes and separation devices, functional smart coatings, fuel and solar cells, catalysts, sensors, etc.

Applications of hybrid organic–inorganic nanocomposites

The purpose of this critical review is to give a representative and comprehensive overview of the arising developments in the field of magnetic metal–organic frameworks, in particular those containing cobalt(II). We examine the diversity of magnetic exchange interactions between nearest-neighbour moment carriers, covering from dimers to oligomers and discuss their implications in infinite chains, layers and networks, having a variety of topologies. We progress to the different forms of short-range magnetic ordering, giving rise to single-molecule-magnets and single-chain-magnets, to long-range ordering of two- and three-dimensional networks (323 references).

Magnetic metal-organic frameworks.

A newly developed class of paraffin-like organomagadiite intercalates, interlayered by primary, secondary, tertiary, and quaternary onium ions, has been used to form elastomeric polymer-layered silicate nanocomposites by in situ polymerization during the thermoset process. Depending on the nature of the onium ions, intercalated or exfoliated magadiite nanocomposites were obtained. The exfoliated nanocomposites were typically disordered, but a new type of exfoliated structure also was observed in which the nanolayers were regularly spaced over long distances (e.g., ∼80 A Bragg spacings). The tensile properties of the polymer matrix were improved greatly by the reinforcement effect of the silicate nanolayers. Exfoliated silicate nanolayers were more effective than intercalated assemblies of nanolayers in optimizing reinforcement. Interestingly, organomagadiite exfoliation in the rubbery epoxy matrix improves the elongation-at-break while improving tensile strength, which is opposite to the behavior of conve...

Hybrid Organic−Inorganic Nanocomposites: Exfoliation of Magadiite Nanolayers in an Elastomeric Epoxy Polymer

Recent developments in the study of the intercalation of organoammonium ions into layered silicates are reviewed. The new developments of the applications of the organoammonium-exchanged layered silicates include the selective adsorption of toxic compounds from water, the immobilization of photo and electroactive species to construct novel photo and electrofunctional materials, and the complexation with organic polymers for the enhancement of the mechanical properties. The conversion of the layered solids to three dimensional nanoporous solids with novel microstructures and adsorptive properties has also been successfully done. The novel controlled properties achieved by the modification with the adsorption of organoammonium ions open new opportunities to tailor the properties of the inorganic-organic nanostructured materials.

Preparation of Inorganic–Organic Nanocomposites through Intercalation of Organoammonium Ions into Layered Silicates

Silanol groups (Si–OH) present at the surface of amorphous silica and microcrystalline silicates can react with organosilicon compounds to form stable organic derivatives1–3. The grafting reaction always occurs at the external surfaces of these materials. The present work considers the intracrystalline grafting on internal Si–OH groups in certain layer silicic acids. For the reaction to occur, the silicic acid must have been expanded by the intercalation of appropriate organic polar molecules such as dimethylsulphoxide; in this way, the individual layers of the silicic acid can be separated and the internal Si–OH groups become accessible to the grafting reagents. The resulting grafted products are organosilicic compounds which retain the lamellar structure of the starting silicic acids, but with the interlamellar surfaces covered by organic groups homogeneously distributed. These materials can be thought of as planar silicones.

Intracrystalline grafting on layer silicic acids

The formation process of the layered silicic acid H-magadiite, obtained after hydrochloric acid treatment of magadiite, has been studied by IR and (/sup 1/H and /sup 23/Na) NMR spectroscopies combined with x-ray diffraction, chemical, and thermogravimetric analyses. This study shows that magadiite is a hydrogen silicate of layer structure, in which the negative charge of the layers is compensated by sodium ions or by protons (Si-O/sup /minus//Na/sup +//Si-OH ratio /approx/ 2/3). The progressive exchange of sodium ions by protons decreases the average H-H distance between OH groups from /approx/ 4 /angstrom/ in H-magadiite to /approx/ 2.5 /angstrom/ in H-magadiite. When all the sodium ions have been exchanged, the silicic structure collapses as a consequence of the establishment of hydrogen bonds between adjacent layers. These interactions prevent the interlayer water adsorption in H-magadiite. 18 references, 7 figures, 1 table.

Proton-sodium exchange in magadiite. Spectroscopic study (NMR, IR) of the evolution of interlayer OH groups

${\mathrm{Co}}_{2}(\mathrm{OH})({\mathrm{PO}}_{4})$ has been prepared from hydrothermal synthesis and characterized from powder x-ray diffraction. The nuclear and magnetic structures have been determined by neutron (D2B and D1B) diffraction data. The structure consists of a three-dimensional framework in which $\mathrm{Co}(1){\mathrm{O}}_{5}$-trigonal bipyramid dimers and $\mathrm{Co}(2){\mathrm{O}}_{6}$-octahedra chains are simultaneously present. The EPR spectrum of ${\mathrm{Zn}}_{2}(\mathrm{OH})({\mathrm{PO}}_{4}):0.1%\mathrm{Co}$ at 4.2 K shows a strong anisotropy of the g factor. The values obtained for the g tensor and the hyperfine coupling constants for the octahedral symmetry were ${g}_{1}=5.890,$ ${g}_{2}=4.550,$ and ${g}_{3}=2.021$ and ${A}_{1}=240\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{\ensuremath{-}1},$ ${A}_{2}=155\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{\ensuremath{-}1},$ and ${A}_{3}=85\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}{\mathrm{cm}}^{\ensuremath{-}1}.$ Signals corresponding to the five-coordinated Co(II) ions were also observed. Magnetization measurements show the presence of two maxima at circa 75 and 15 K, respectively. The first peak was attributed to a three-dimensional antiferromagnetic ordering and the second one reveals the existence of a spin-glass-like state. This state with a cooperative freezing was also confirmed by both ac susceptibility measurements and magnetic irreversibility observed in the zero-field-cooled--field-cooled signals. From low-temperature neutron-diffraction data, antiferromagnetic ordering is established with an ordering temperature of 71 K. The propagation vector of the magnetic structure is $k=[0,0,0].$ The magnetic moments at 1.7 K are ferromagnetically coupled between ${\mathrm{CoO}}_{6}$-octahedra chains and the ${\mathrm{Co}}_{2}{\mathrm{O}}_{10}$ dimers in the z direction. The values obtained for the magnetic moments are: $3.39(7){\ensuremath{\mu}}_{B}$ [Co(1)] and $3.84(5){\ensuremath{\mu}}_{B}$ [Co(2)]. The absence of any anomaly in both the specific heat and thermal evolution of the magnetic moments below \ensuremath{\sim}20 K confirms the blocking process of a spin glass behavior. The crystal-field splitting of the ${\mathrm{Co}}^{2+}$ ions causes a single ion anisotropy along the z (c-axis) direction, giving an Ising character in which the local spins from the Co(1) dimers are frozen. A magnetic frustration in the Co(1) magnetic moments is observed as due to the presence of antiferromagnetic interactions between Co(2) neighbor chains. It is to note the existence of a $\mathrm{Co}(1)\ensuremath{-}\mathrm{O}(3)({\mathrm{PO}}_{3})\ensuremath{-}\mathrm{Co}(2)$ superexchange angle with a value of 107\ifmmode^\circ\else\textdegree\fi{} that involves ferromagnetic couplings between chain and dimer neighbors ferromagnetically coupled. This exchange pathway together with the anisotropy and frustration could be the responsible of the spin glass behavior observed in the three-dimensional antiferromagnetic ${\mathrm{Co}}_{2}(\mathrm{OH})({\mathrm{PO}}_{4})$ ordered phase.

http://repositorio.unicamp.br/jspui/bitstream/REPOSIP/74387/1/WOS000178383200060.pdf

Spin-glass behavior in a three-dimensional antiferromagnet ordered phase: Magnetic structure of Co 2 (OH)(PO 4 )

The Co2−xCux(OH)PO4 (0 ≤
				x
				≤ 2) solid solution was prepared from hydrothermal synthesis Neutron powder diffraction patterns show that the Co2+ and Cu2+ ions are simultaneously present in both the [MO4(OH)2] octahedra and the [MO4(OH)] distorted trigonal bipyramid topologies The evolution of the lattice parameters follows Vegard’s law in the whole range of substitution This study allowed us to determine correctly the a and b crystallographic parameters of the Cu2(OH)PO4 phase which were interchanged in the literature The magnetic behaviour in the cobalt–copper compounds indicates the existence of overall antiferromagnetic interactions as predominant Three-dimensional magnetic ordering with critical temperatures of 69, 64, 60 and 47 K for x = 01, 03, 05 and 1 respectively is observed The magnetic study of Co19Cu01(OH)PO4 suggests a spin-glass like state below 10 K AC measurements obtained at different frequencies and applied fields confirm the freezing process in Co19Cu01 and the long range interactions in the Co2−xCux(OH)PO4 (x
				≤ 1) phases For x > 1, the magnetic dimensionality decreases with the increase of Cu(II) amount being of short range for x = 2 These results are attributed to the presence of the unpaired electron in the dx2−y2 orbital and the absence of overlap between neighbour ions Specific-heat measurements confirm the evolution to a short range magnetic system with the Cu(II) amount From low-temperature neutron diffraction data, it can be observed that the existence of antiferromagnetic order for x
				≤ 1 is originated by the antiparallel ordering of both ferromagnetic linear octahedral chains and trigonal bipyramidal dimers The propagation vector is k = [0,0,0] and the magnetic moments are aligned in the z direction The values of the main magnetic exchange pathways [M–O–M] are characteristic of ferro- and antiferromagnetic couplings with a superexchange ferromagnetic angle, M(1)–O(3)–M(2) of 107–109°, which plays an important role in the competition of the freezing process These results are explained on the basis of both the electronic configuration and the correlations between structural and magnetic properties

J. M. Rojo

Papers

Intracrystalline grafting on layer silicic acids

Proton-sodium exchange in magadiite. Spectroscopic study (NMR, IR) of the evolution of interlayer OH groups

Spin-glass behavior in a three-dimensional antiferromagnet ordered phase: Magnetic structure of Co 2 (OH)(PO 4 )

Magnetic evolution of the antiferromagnetic Co2−xCux(OH)PO4 (0 ≤x≤ 2) solid solution. A neutron diffraction study

Structural and Spectroscopic Study of the (Mg, Ni)2(OH)(AsO4) Arsenates