Aluminum 2-Methoxyethoxide: An Internally Coordinated Aluminum Alkoxede

Abstract

Aluminum 2-methoxyethoxide was isolated and characterized by ¹H, ¹³C and ²⁷Al NMR. The ²⁷Al NMR and mass spectra show that the compound is an internally coordinated dimer. This aluminum alkoxide is less susceptible to hydrolysis in comparison to other aluminum alkoxides.     

Sol-Gel Synthesis of Potassium Titanyl Phosphate: Solution Chemistry and Gelation

The solution chemistry and aggregation mechanisms involved in sol-gel synthesis of potassium titanyl phosphate (KTP) are studied in detail. The chemistry of the metal precursors are shown to be critical for the formation of the desired KTP phase. The precursor solution as well as some preparation intermediates were studied by several spectroscopic methods to determine the structure of the organometallic species present in these solutions. The structural evolution taking place in the solution after hydrolysis was studied using photon correlation spectroscopy and small angle X-ray scattering techniques. The influence on the gelation of several preparation parameters such as, the precursors chemistry, the mixing order of the metal alkoxides, the solvent/KTP ratio and the water/KTP molar ratio was also examined.     

Control of the morphology and particle size of boehmite nanoparticles synthesized under hydrothermal conditions

The spontaneous nucleation under hydrothermal conditions often leads to aggregation of crystallizing particles, which is an undesired phenomenon when the goal is the preparation of nanocrystals with narrow particle size distribution. The present paper reports on the synthesis of boehmite nanocrystals under hydrothermal conditions. An aqueous aluminum chloride salt solution was first prepared, and the pH was increased to 11 using a 5 M sodium hydroxide solution. The hydrothermal treatment was performed at 160 degrees C for different periods of time. The system yielded relatively small (15-40 nm) boehmite crystallites aggregated into larger (160 nm) particles. To avoid the aggregation, a biocompatible polymer, sodium polyacrylate (NaPa) 2100, was employed as a size-/morphology-controlling agent. Thus, stable colloidal suspensions of rounded boehmite nanoparticles having a size between 15 and 40 nm were obtained at 160 degrees C for 24 h. Further, the effect of synthesis time on the morphological features of boehmite synthesized in such a NaPa-containing system was investigated. The increase of the synthesis time from 24 to 168 h resulted in the formation of very long boehmite fibers (1000-2000 nm) with an average diameter of about 10 nm. The boehmite samples were characterized by XRD, DLS, TEM, IR, N2 adsorption, and zeta potential measurements. The colloidal stability of the obtained suspension was also studied.     

Synthesis of boehmite and hematite by joint hydrolysis of carbamide,aluminum chloride,and iron(III) chloride under hydrothermal conditions

The formation of boehmite and hematite in dependence of the conditions of joint hydrothermal hydrolysis of carbamide and a mixture of aluminum and iron(III) chlorides in the presence of K, Na, Ca, and Mg chlorides at T = 160–200°C and P = 0.6–1.6 MPa was studied. It was shown that the amount of boehmite and hematite being formed in hydrolysis of Al and Fe chlorides strongly depends on pressure, temperature, hydrolysis duration, and composition of the model mixture of Al, Fe, Mg, Ca, K, and Na chlorides. It was found that a complete hydrolysis of AlCl₃ and FeCl₃ with 99% yield of boehmite and hematite occurs at the stoichiometric ratio between carbamide and aluminum and iron chlorides in the starting solution, whereas mostly iron oxyhydroxide [goethite FeO(OH)] and aluminum oxychloride [Al₁₇O₁₆(OH)₁₆Cl₃] are formed at nonstoichiometric ratios.     

The role of precursors in the structure of SiO2-Al2O3 sols and gels by the sol-gel process

Binary sols and gels of SiO₂-Al₂O₃ were prepared using tetraethyl orthosilicate and each of four aluminum compounds; aluminum di (sec-butoxide) ethylacetoacetic ester chelate (AC), aluminum nitrate nonahydrate (AN), aluminum formoacetate (AF), and boehmite sol (BS) made from aluminum i-propoxide. The structure and the evolution of the Si-O-Al bonds in SiO₂-Al₂O₃ sols and gels were investigated by ²⁷Al nuclear magnetic resonance (NMR), Infrared absorption spectra, DTA, and X-ray diffraction. The formation of Si-O-Al bonds differs depending on the aluminum compounds used as raw materials. The ratio of Al(IV) to {Al(IV) + Al(VI)} is related to the microstructural homogeneity of the gels. When AC is used as a raw material, the Si-O-Al bonds are formed in the sol state and resultant gel shows good microstructural homogeneity. In case of AN, the Si-O-Al bonds are not formed either in the sol or the wet gel state. The bonds are formed by drying the gel before heat-treatment temperature reaches 300 400°C, resulting in good microstructural homogeneous gel. When AF is used, the Si-O-Al bonds are formed in the sol state but the ratio of Al(IV) to {Al(IV) + Al(VI)} is lower than when using AC. Microstructural homogeneity of the gel is ranked between AC or AN and BS. Using BS, the Si-O-Al bonds are not formed in the sol solution, and the change in the coordination number of the gel is similar to that of boehmite gel. The Microstructural homogeneity of the gel is the worst among the BS gels, which were prepared by using the four aluminum raw materials.     

Studies of mixed silica/alumina and silica/boric oxide materials

Multinuclear low temperature solution NMR and FTIR has been used to monitor the hydrolysis and polymerisation chemistry involved in the preparation of multicomponent silica/alumina and silica/boric oxide monolithic gels. Pre-hydrolysis of the silicon component (tetraethylorthosilicate) in the presence of low levels of water is an important factor in obtaining transparent materials. In order to obtain high homogeneity and minimise the subsequent precipitation of the fastest hydrolysing component, ethylacetonate (etac) has been used to modify the aluminum alkoxides. Solid state nmr and FTIR studies show that the borosilicate system contains Si-O-B bonds during the early stages of polymerisation but they are absent on final gelation. Thermal treatment to around 500°C is required to generate mixed Si-O-B bonds. Length of prehydrolysis has little affect on the nature of the Si-O-B gel materials but has a significant effect on the chemical nature of Si-O-Al materials. Longer silicon alkoxide prehydrolysis times lead to better defined materials.formerly Carole C. Perry.formerly at Chemistry Department, Brunel University, Uxbridge, Middlesex. UB8 3PH UK.     

Growth and surface properties of boehmite nanofibers and nanotubes at low temperatures using a hydrothermal synthesis route

The growth of boehmite nanostructures at low temperature using a soft chemistry route with and without (PEO) surfactant is presented. Remarkably long boehmite 1D nanotubes/nanofibers were formed within a significantly short time by changing the reaction mechanism of aluminum hydroxide. By using the PEO surfactant as a templating agent, boehmite nanotubes up to 170 nm in length with internal and external diameters of 2-5 and 3-7 nm, respectively, were formed at 100 degrees C. A slightly higher temperature (120 degrees C) resulted in the formation of lath-like nanofibers with an average length of 250 nm. Using the cationic surfactant CTAB, nanotubes rather than nanofibers were formed at 120 degrees C. Without surfactant, nanotubes counted for around 20% of the entire sample. A regular interval supply of fresh boehmite precipitate resulted in a larger crystallite size distribution of nanotubes. The morphology of nanotubes was more uniform in samples without the regular addition of aluminum hydroxide. Moreover, for the same hydrothermal time, the final nanotubes for nanomaterials without a regular interval supply of fresh aluminum hydroxide precipitate were longer than those with a regular aluminum hydroxide precipitate supply, which is in contrast to previously published results. Higher Al/PEO concentrations resulted in the formation of shorter nanotubes. A detailed characterization and mechanism are presented.     

Preparation of nanostructured thin films of yttrium aluminum garnet (Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>) by Sol—Gel technology

The synthesis of hydrolytically active heteroligand coordination compounds [M(C₅H₇O₂)_3–x(C₅H₁₁Oⁱ)_x] (where M = Al³⁺ and Y³⁺) using aluminum and yttrium acetylacetonates has been studied. The gel formation kinetics in their solutions upon hydrolysis and polycondensation has also been studied. Thin films of a solution of these precursors have been applied to polished sapphire substrates by dip coating. The crystallization of nanostructured yttrium aluminum garnet (Y₃Al₅O₁₂) films during heat treatment of xerogel coatings under various conditions has been studied. How the phase composition, microstructure, and particle size depend on the synthesis parameters has been recognized.     

Dependence of the27Al and31P NMR chemical shifts in alumophosphates on the composition of the second coordination sphere

Conclusions The isotropic²⁷Al NMR chemical shifts in alumophosphates in the solid state and alumophosphate complexes in solution vary additively upon substitution of water by phosphate ions in the aluminum coordination sphere, while the³¹P NMR chemical shifts of phosphate vary additively depending on the number of coordinated aluminum atoms.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2340–2342, October, 1987.     

Structural characterization of C-S-H and C-A-S-H samples—Part II: Local environment investigated by spectroscopic analyses

Spectroscopic studies (¹H, ²³Na and ²⁷Al MAS NMR and Raman spectroscopy) have been used to characterize three series of C-S-H samples (0.8<Ca/Si<1.7): one C-S-H series, one aluminum inserted C-S-H series (named C-A-S-H series), and one sodium and aluminum inserted C-S-H series (named C-N-A-S-H series). Previous Rietveld analyses have been performed on the two first series and have clearly shown that (1) a unique ‘tobermorite M defect’ structural model allows to describe the C-S-H structure whatever the Ca/Si ratio and (2) the insertion of aluminum into the C-S-H structure led to the degradation of the crystallinity and to a systematic increase of the basal spacing of about 2 Å regardless the Ca/(Si+Al) ratio (at a constant Al/Si ratio of 0.1). Spectroscopic investigations indicate that the main part of the Al atoms is readily incorporated into the interlayer region of the C-S-H structure. Al atoms are mainly inserted as four-fold coordinated aluminates in the dreierketten silicate chain (either in bridging or paired tetrahedra) at low Ca/Si ratio. Four-fold aluminates are progressively replaced by six-fold coordinated aluminates located into the interlayer region of the C-S-H structure and bonded to silicate chains. Investigation of the hydrogen bonding in C-S-H indicates that the main part of the hydrogen bonds is intra-main layer, and thus explains the low stacking cohesion of the C-S-H structure leading to its nanometric crystal size and the OD character of the tobermorite like structures.     

Crystallization of Sol-Gel Boehmite via Hydrothermal Annealing

Thin crystallites of boehmite were synthesized by annealing a sol-gel precursor under hydrothermal conditions. Samples were characterized with X-ray powder diffraction, thermogravimetry, transmission electron microscopy, and by refining the crystalline phases. Fresh samples consisted of boehmite sheets forming folded paper-like “crystallites,” which were transformed into thin flat crystalline plates perpendicular to crystallographic b-axis when they were annealed under hydrothermal conditions using water as mineralizer. Boehmite's crystallite size increased with the annealing time. The rhombic boehmite crystallites had their shortest diagonal parallel to crystallographic a-axis, and their lateral faces parallel to {101} planes forming an angle of 104.32° between each other; these planes contained active aluminum atoms responsible for the crystallites growing along them. The hydrogen bonding length, which decreased as crystallite size increased, determined the variation of boehmite's transition temperature into γ-alumina. Since this transformation is pseudo-morphic, both particle morphology and sample porosity of alumina were determined by the arrangement of crystallites in boehmite. γ-Alumina crystallite distribution had memory about boehmite crystallite dimensions and atomic arrangement: crystallites were oriented parallel to boehmite’s a axis, and were confined by boehmite's crystallite dimensions.     

A New Method of Synthesis of Nanosized Boehmite (AlOOH) Powders with a Low Impurity Content

A new method of synthesis of nanosized aluminum oxyhydroxide (AlOOH, boehmite) powders has been suggested through a hydrothermal treatment of nanosized γ-Al₂O₃ powder in water and a 1.5 wt % HCl solution at different temperatures. It has been found that hydrothermal treatment in a 1.5 wt % HCl solution leads to the purification of the starting material; different treatment durations allow one to obtain boehmite particles of different shape. It has been demonstrated that a nanosized boehmite powder is obtained upon the hydrothermal treatment of a nanosized γ-Al₂O₃ in water above 80°С. The nanosized boehmite powders synthesized at different temperatures have been studied by various methods.     

Structural investigations on the hydrolysis and condensation behavior of pure and chemically modified alkoxides. 2. Germanium alkoxides

Structural investigations on the hydrolysis and condensation behavior of germanium alkoxides were for the first time performed by means of X-ray absorption fine structure and Raman spectroscopy. The studies reveal that germanium alkoxides are monomeric in nature and undergo very fast hydrolysis and condensation reactions upon water addition. However, the chelation of germanium alkoxides by acetylacetone does not take place even 48 h after mixing, and any change in hydrolysis and condensation behavior is not observed after acetylacetone addition. When mixed with prehydrolyzed silicon alkoxide, the structures of germanium alkoxides are not modified. Both Si and Ge precursors are insensitive to the presence of each other in the reaction solution even after 48 h of aging. The addition of water to this mixture catalyzes the hydrolysis and condensation reactions very fast and leads to the formation of Ge-O-Ge (and consequently Si-O-Si) homocondensation products.     

Hexane Cracking over Steamed Phosphated Zeolite H‐ZSM‐5: Promotional Effect on Catalyst Performance and Stability

The nature behind the promotional effect of phosphorus on the catalytic performance and hydrothermal stability of zeolite H‐ZSM‐5 has been studied using a combination of ²⁷Al and ³¹P MAS NMR spectroscopy, soft X‐ray absorption tomography and n‐hexane catalytic cracking, complemented with NH₃ temperature‐programmed desorption and N₂ physisorption. Phosphated H‐ZSM‐5 retains more acid sites and catalytic cracking activity after steam treatment than its non‐phosphated counterpart, while the selectivity towards propylene is improved. It was established that the stabilization effect is twofold. First, the local framework silico‐aluminophosphate (SAPO) interfaces, which form after phosphatation, are not affected by steam and hold aluminum atoms fixed in the zeolite lattice, preserving the pore structure of zeolite H‐ZSM‐5. Second, the four‐coordinate framework aluminum can be forced into a reversible sixfold coordination by phosphate. These species remain stationary in the framework under hydrothermal conditions as well. Removal of physically coordinated phosphate after steam‐treatment leads to an increase in the number of strong acid sites and increased catalytic activity. We propose that the improved selectivity towards propylene during catalytic cracking can be attributed to local SAPO interfaces located at channel intersections, where they act as impediments in the formation of bulky carbenium ions and therefore suppress the bimolecular cracking mechanism.     

New synthesis of mullite. Structural evolution study by 17O, 27Al and 29Si MAS NMR spectroscopy

Mullite has been prepared from a new combination of precursors. An aluminum alkoxide, aluminium isopropoxide, and silicon tetrachloride, are hydrolysed in tetrahydrofuran solution by ¹⁷O enriched water. The resulting powder is chemically homogeneous, crystallizing into mullite at 980°C. The structural evolution has been studied by DTA, TGA, XRD and ¹⁷O, ²⁷Al and ²⁹Si MAS NMR spectroscopy.     

Heptacoordinated diphenyllead; hexa- and pentacoordinated triphenyllead and tin compounds derived from 5H-benzimidazo[1,2-c]quinazoline-6-thione

Heptacoordinated diphenyllead; hexa- and pentacoordinated triphenyllead and tin compounds derived from 5H-benzimidazo[1,2-c]quinazoline-6-thione are reported. The same molecular structures were found in solution by ¹¹⁹Sn and ²⁰⁷Pb NMR and in the solid state by X-ray diffraction analysis. The ligand was bound through S and N giving a four-membered ring. Due to the tension of the chelate ring in the penta- and hexacoordinated compounds, the nitrogen approaches the metal atom from an oblique direction giving a weak coordination. Hexacoordinated metal atoms were obtained by Lewis bases coordination to the polycyclic tin and lead compounds, which was possible because the M-phenyl groups form a cavity that allows the bases to approach from the opposite direction to the sulfur atom. In some crystals, two molecules formed a cavity where a solvent molecule was included. A heptacoordinated diphenyllead bound to two ligands and having the less common pentagonal bipyramidal geometry and cis-mer configuration with two sulfur atoms lying very close together was obtained.     

Changes in Coordination Number of Co Ion and Fluorescence Spectrum of 1-Naphthol during the Sol-Gel Reaction of TEOS

Changes in coordination number of Co²⁺ and fluorescence spectra of 1-naphthol during the sol-gel transitions of TEOS have been investigated as a function of time. The change in the coordination number of Co²⁺ has been observed as follows. Six-coordinated Co²⁺ decreased quickly within several hours in the first stage of the reaction corresponding to water consumption by initial hydrolysis reaction. Then six-coordinated Co²⁺ increased around gelation due to polycondensation. After the gelation four-coordinated Co²⁺ increased, where isomorphous-replacement of Co²⁺ into the –O–Si–O– networks occurred. In the Co²⁺/1-naphthol mixed system, separate ion pair of 1-naphthol is preferentially coordinated on the six-coordinated Co²⁺ where water molecule(s) plays an important role to geometrical relaxation of excited-state 1-naphthol.     

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H₂SO₄. The samples prepared with HCl were additionally sulfated with a 1 M solution of H₂SO₄. Characterization was performed with FTIR and ²⁹Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO₂-SiO₂ system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m²/g were obtained.     

Hydration of alumina cluster anions in the gas phase

Hydration reactions of anionic aluminum oxide clusters were measured using a quadrupole ion trap secondary ion mass spectrometer, wherein the number of Lewis acid sites were determined. The extent of hydration varied irregularly as cluster size increased and indicated that the clusters possessed condensed structures where the majority of the Al atoms were fully coordinated, with a limited number of undercoordinated sites susceptible to hydrolysis. For maximally hydrated ions, the number of OH groups per Al decreased in an exponential fashion from 4.0 in Al(1) cluster to 1.4 in the Al(9) cluster, which was greater than that expected for a highly hydroxylated surface but less than that for solution phase alumina clusters.     

17O-NMR spectroscopy to study the coordination of oxygen-based ligands to lanthanide ions in solution

The number of oxygen-based ligands coordinated to lanthanide ions influences the physical and chemical properties of lanthanide complexes, making this number important to study. We used peak shifts in ¹⁷O-NMR spectroscopy to determine the number of individual nonhydroxyl-oxygen-based ligands coordinated to Dy³⁺. Oxygen-containing organic solvents were used as models to represent oxygen-based ligands to explore the scope of the technique because they contain a range of functional groups that have different electron-donating abilities and steric bulk. The measured coordination numbers of dimethylformamide, dimethyl sulfoxide, acetone, diethyl ether, tetrahydrofuran, di-isopropyl ketone, and hexamethyl acetone were consistent with reasonable values, indicating that ¹⁷O-NMR spectroscopy is a useful technique to study the coordination chemistry of nonhydroxyl ligands to lanthanide ions in solution.