Metal alkoxides Ti

Figure 1 Molecular structure of some transition metal alkoxides Ti(OPr )4 monomer (1) [Zr(OPF)4(PFOH)]2 dimer (2) [Ti(OEt)4]3 trimer (3)...

These ion exchange materials are synthesized via the hydrolytic reaction of NaOH and water with the metal alkoxides Ti(0C3H7)it, Nb(0C2H5)5, and ZrCOC Hg) as illustrated for preparation of sodium titanate (Eqn l). 

Metal-organic compounds Metal alkyls - AlMe3 and Ti(CH2tBu)4 Metal alkoxides - Ti(OiPr)4, etc. 

The important role of steric congestion around the central atom in determining the composition of the final product has also been demonstrated during the reactions of other metal alkoxides [Ti(OPr )4, Zr(OPr )4.PPOH, M(OPP)5 with M = Nb or Ta, Al(OPr )3, Sb(OPr )3) with sterically hindered phenols (HOC6H3Mc2-2,6 HOCeHsPr -2,6 HOC6H3Bu 2-2,6]. 

Hybrid polymer materials are synthesised by the sol-gel process through the controlled hydrolysis and condensation of organically modified Si-alkoxides. Cocondensation with other metal alkoxides (Ti-, Zr-, Al-alkoxides) is also possible (Fig. 6.2). 

Detailed information on the synthesis of PEBA is presented in Chapters 2 and 10 and also in [13-16]. However, it is worth mentioning here that commercially available poly (ether- -amide) PEBAX copolymers are synthesized by melt polycondensation of carboxylic acid-terminated amide blocks with poly-(oxyalkylene glycol)s. The polymerization is catalyzed by a metal alkoxide Ti(OR)4 and is carried out at elevated temperatures of ca. 230°C under vacuum. These copolymers are marketed for use in many areas, a few of which include sports equipment, automotive components, applications that require polymers with antistatic properties, and also in biomedical applications, such as tubing and catheter balloons [17]. There is also a growing body of literature on the use of PEBAX in the manufacture of membranes for gas separations. Vestamid E-Series elastomers marketed by Degussa-Htils are another commercial example of PTMO-PA12 based PEBA copolymers. 

Besides direct hydrolysis, heterometaHic oxoalkoxides may be produced by ester elimination from a mixture of a metal alkoxide and the acetate of another metal. In addition to their use in the preparation of ceramic materials, bimetallic oxoalkoxides having the general formula (RO) MOM OM(OR) where M is Ti or Al, is a bivalent metal (such as Mn, Co, Ni, and Zn), is 3 or 4, and R is Pr or Bu, are being evaluated as catalysts for polymerization of heterocychc monomers, such as lactones, oxiranes, and epoxides. An excellent review of metal oxoalkoxides has been pubUshed (571). 

In mixtures of nonpolar solvents with little water, surfactants form spherical reverse micelles. They have a reversed orientation of the molecules with the hydrophilic groups in the interior and a drop of enclosed water in the middle. Starting from a precursor material, metal oxides in the form of uniform nanosized spheres can be obtained by hydrolysis under controlled conditions (pH, concentration, temperature). For example, titanium oxide spheres are obtained from a titanium alkoxide, Ti(OR)4 + 2 H20 —t Ti02 + 4 ROH. 

The most common sol-gel process employs metal alkoxides of network forming elements (M(0R) where M is Si, B, Ti, Al, etc. and R is often an alkyl group) as monomeric precursors. In alcohol/water solutions the alkoxide groups are removed stepwise by hydrolysis reactions, generally employing acid or base catalysts, and are... 

The sol-gel synthesis of siloxane-based hybrid organic-inorganic implants usually involves di- or trifunctional organosilanes co-condensed with metal alkoxides, mainly Si(OR)4 and Ti(OR)4. As we will see in this section, the incorporation of Ca salts is a common strategy to provide bioactivity at the systems. Each of these components has specific roles that will be reviewed and discussed. 

These reactions have been studied in detail for materials such as silica, and understanding of reaction mechanisms, as well as of the role of the precursor and catalyst (acid or base), has been well documented.63,64 Similar studies have been carried out in other material systems, most notably, lead zirconate titanate [Pb(Zr,Ti)03 PZT].52,65-68 For multicomponent (mixed-metal) systems such as those noted, prehydrolysis of less reactive alkoxides is sometimes employed to improve solution compositional uniformity. Other synthetic strategies to achieve molecular level mixing of reagents have also been employed. Here, synthesis of mixed-metal alkoxides has been a focus of investigators.40-42 A key point is to restrict the amount of water and to control how it is added to form solubalizable precursor species, rather than to induce precipitation.1,52,69,70... 

In some instances, this approach has proven successful, with comparatively low crystallization temperatures being observed. For example, Eichorst and Payne in the synthesis of LiNb03 noted crystallization temperatures of 400-500 °C for a mixed-metal alkoxide precursor.111 In other instances, these attempts have proven less successful. Numerous attempts have been made to synthesize Pb-Zr and Pb-Ti precursors, each with the 1 1 cation stoichiometry of the desired PbZr03 and PbTi03 compounds.83,84 Unfortunately, 1 1 stoichiometric ratio compounds have not always been obtained, with crystalline compounds of other stoichiometries precipitating from the solution, as illustrated in Fig. 2.11.83 This figure shows the crystal structure of PbTi2[p(4)—... 

The practical use of the desorption reaction requires a catalyst for the improvement of the kinetics. The first work on catalyzed alanates at MPI - Miilheim was derived from studies that used transition-metal catalysts for the preparation of MgH2- The NaAlH4 was doped with Ti by solution chemistry techniques whereby nonaqueous liquid solutions or suspensions of NaAlH4 and either TiCl3 or the alkoxide Ti(OBu )4 [titanium(IV) w-butoxide] catalyst precursors were decomposed to precipitate solid Ti-doped NaAlH4 [57, 58]. 

Definitions. Colloids are solid particles with diameters of 1 100 nanometers, A sol is a dispersion of colloidal particles in a liquid. A gel is an interconnected rigid network of sub-micrometer dimensions. A gel can be formed from an array of discrete colloidal particles (Method I) or the 3-D network can be formed from the hydrolysis and condensation of liquid meial alkoxide precursors (Methods 2 and 3). shown in Fig. 11. The metal alkoxide precursors used in Methods 2 and 3 are usually Si(OR)4 where R is CHj. C-Hj. or C3H7. The metal ions can be Si, Ti. Sn. Al, and so on,... 

Other reports confirm similar reaction of C02 with metal alkoxide compounds. Benzene solutions of the alkoxide compounds Ti(OBu")4, Zr(OBu")4, Zr(OEt)4, Nb(OEt)5, and Fe(OEt)3 were found to absorb carbon dioxide in various amounts (151). Only Zr(OBu")4 reacted with an amount approaching one equivalent per metal complex. The solution ir spectra indicate formation of coordinated organic carbonates. From this evidence, equilibrium formation of the species M(0R) 1(02C0R) under 1 atm of C02 is inferred. 

Figure 1 Prototypal structures for small oligomeric metal alkoxides (a) the cubane-M404 unit in [TKOMe) , and [Na(OBu )]4 (b) die planar [CufOBu1) , structure (c) and (d) fused trigonal and fused trigonal-tetrahedral units as seen in [Be(OR)2) compounds, where n = 3 and 2 (e) fused tetrahedral-octahedral units seen in [Al(OPri)3]4 (f) edge-shared tetrahedra as in [Al(OBu )3]2 (g) fused octahedra as in [MfOEt), , where M = Ti, V, W and (h) edge-shared octahedra as...

One approach to making such powders is the sol-gel method, in which a metal oxide powder is synthesized from a metal alkoxide, a compound derived from a metal and an alcohol. In the synthesis of titania (Ti02) from titanium ethoxide, Ti(OCH2CH3)4, for example, the Ti(OCH2CH3)4 starting material is made by the reaction of titanium(IV) chloride with ethanol and ammonia in a benzene solution ... 

In 1986 Yoldas performed one of the first detailed studies of the morphology of Ti(OR)4 and Zr(OR)4 hydrolysis products as a function of their thermal treatment, metal alkoxides concentrations in solutions, h ratio, and pH or acid content in the hydrolysis agent. [1793]. The range of concentrations where fibers could be drawn in the system Ti(OPri)4-H20-EtOH-HCl was determined by Kamiya [872],... 

Crystallization of BaTi03 and Ba,.xSrxTi03 solid solutions may also occur on aging at 30 to 90°C of gels prepared by hydrolysis in methoxyethanol of complex metal alkoxides usually Ba and Sr ethoxides and Ti(OPr )4 are used [588, 1470, 1474],... 

In [1677] complex alkoxides and alkoxide-carboxylates were compared as precursors for preparation ofBST films. In contrast to the introduction of alkaline earth carboxylates in the form of preliminary isolated salts, in this work metal alkoxide solution in methoxyethanol containing titanium and alkaline-earth metal was modified by addition of 2-ethylhexanoic acid with subsequent slow distilling off the solvent and repeated dilutions with fresh portions of methoxyethanol. During the distillation process, part of the alkoxide groups are substituted by the 2-ethylhexanoate ligands. The exchange reaction of Ti(OPr )4 with acid was studied in different solvents, and it was demonstrated that in the course of distillation the titanium oxoisopropoxy-2-ethylhexanoate is formed with elimination of ester ... 

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