Alkoxides complexes

Transition-metal mixed oxides active in combustion catalysis have been prepared by two main procedures i) classical coprecipitation / calcination procedures starting from metal nitrates and/ or alkoxides ii) preparation based on the supercritical drying of gels prepared from organic complexes (alkoxides, acetylacetonates or acetates), producing aerogels . Details on the second preparation can be found in Ref. 13. 

Kato, K. 1998. Low-temperature synthesis of SrBi2Ta209 ferroelectric thin films through the complex alkoxide method Effects of functional group, hydrolysis and water vapor treatment. Jpn. J. Appl. Phys. 37 5178-5184. 

Complex alkoxides of the type [CsOR]n are known, structures of which have not been well defined. It reacts with amines forming amido complexes of the type CsNHR or CsNR2. The structures of crystalline complexes are complicated, depending upon the solvent and other factors. 

Metallotropic rearrangement, in mercury tri-azenide complexes, 30 41 Metals, see also Heterobimetallics specific element Transition metal complex alkoxides, 15 159-297 of actinides, 15 290-293 of alkali metals, 15 260-263 of alkaline earths, 15 264-266 of aluminium, 15 266-272 of beryllium, 15 264-266 double type, 15 293-294 of gallium, 15 266-272 of lanthanides, 15 290-293 of magnesium, 15 264-266 properties of, 15 260 of transition metals, 15 272-290 trialkylsilyloxides, 15 295-297 of zinc, 15 264-266... 

The electrochemical technique can be used also for direct synthesis of bimetallic alkoxides. For instance, the anodic dissolution of rhenium in the methanol-based electrolyte that already contained MoO(OMe)4, permitted to prepare with a good yield (60%) a bimetallic complex RevMov,02(OMe)7, with a single Re-Mo bond [904], Application of the same procedure permitted the preparation of complex alkoxide solutions with controlled composition for sol-gel processing of ferroelectric films [1777]. 

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 ... 

M = Li, Na, K, TI(I)3 Although they allow control of the stoichiometry between the M and M, metals, they have not been much developed so far for species-associating metals involved in electrooptical ceramics. They are mostly limited to the use of the complex alkoxide anion Zr2(OiPr)9, and La-Zr species were recently built up by this route [87]. In contrast with the preceding synthetic routes based on mixing simple compounds, Eq. (19) implies the prior synthesis of a heterometallic alkoxide based on an alkali metal and further removal of the salt. 

When a multicomponent alkoxide is used, the multicomponent or complex alkoxide can be prepared by reacting a combination of single alkoxides or by adding soluble inorganic salts to single or complex alkoxides. The species from an inorganic salt can be incorporated into both multicomponent alkoxides and the alkoxide sol structure itself. If the atom or ion from the salt is to be incorporated into the sol, it must be properly dispersed and then reacted to form the multicomponent oxide. 

Molybdenum, dicyclopentadienyltetracarbonyldi-, 1316 Molybdenum, hexacarbonyl-, 1230 Molybdenum complexes alkoxides, 1307 alkyl, 1307 allyl, 1306 aqua,1230 aryl, 1307... 

A relatively practical approach could be derived from the sol-gel process. If the alkoxides contained several elements in the right proportion, uniformity of composition could be achieved for these elements. The difference with conventional sol-gel method would be to start from building blocks, namely complex alkoxides containing two or several elements, instead of individual bricks. Conceptually, this is the way zeolites are constructed. Zeolites of different compositions and structures can be made because the building blocks are different. Figure 18.4 schematically... 

Compounds Carbonyls, nitrosyls, organometallics phosphine complexes Halides, oxides, aquo complexes alkoxides, ammines. 

Figure 2-12. Proposed structure of Sr-Bi-Ta and Sr-Bi-Nb complex alkoxides (Koto et al., 1998).

PBD-Modified LiNbOs Precursor. Non-modified LiNbOs (STD-LiNbOs) precursor solutions are prepared from LiOEt and Nb(OEt)s in ethanol (Hirano, 2002). The structure of the precursor was confirmed to consist of a complex alkoxide Li[Nb(OEt)6], which was reported by Eichorst et al. (1990) in detail (Eichorst et al., 1990). On the other hand, three types of/6-diketone compounds are selected based upon the number of benzene rings (phenyl groups) in its stmcture. In this case, the coordination of l-phenyl-1,3-butanedione (PBD) to the LiNbOs precursor is confirmed by UV spectra. The similar coordination is also realized in 2,4-pentanedione (PD)- and 1,3-diphenyl-1,3-propanedione (DPPD)-modified LiNbOs precursors, which was confirmed by UV-spectra. The proposed structures of these d-diketone modified LiNbOs precursors are shown in Figure 17-1. 

The acetato-alkoxo Ba-Ti complex, in which titanium alkoxide is associated with barium acetate via acetate bridges (Mosset et al., 1988), yielded BaTiOs ceramic fibers in a similar manner to PbTiOs fibers (Yoko et al., 1990). However, fiber length was limited to several mm probably due to the lack of strong Ba-O-Ti bonds in the precursor gel (later, long BaTiOs fibers were obtained by using the catecohol-complexed alkoxide as a starting material Lu et al., 2002). 

Kim C.E., Park Y.I., Lee H.W. Preparation of PbTiOs fibres using triethanolamine-complexed alkoxide. J. Mater. Sci. Lett. 1997 16 96-100... 

Kulpinski and Nord describe the use of complex alkoxide catalysts for the condensation of aldehydes to glycol esters. These catalysts are of a type represented by Mg[Al(0R)4]2, a substance that evidently consists of Mg" ions and A1(0R)4" ions. With aldehydes having —CH2— in the alpha position, this catalyst produces mainly glycol esters. However, with aldehydes having —CHR— in the alpha position, mainly simple esters are formed. Although these reactions may seem puzzling at first, they are readily understood when the amphoteric nature of the aldehydes and the catalysts is taken into consideration, from the viewpoint of the electronic theory of acids and bases. 

The esters thus produced are glycol esters and involve a reaction of the aldehyde in two stages, the first of which is base-catalyzed (aldolization) and the second is acid catalyzed (ester formation). These glycol esters will be formed with an amphoteric catalyst or a complex catalyst such as the complex alkoxides. 

Strongly basic alkoxide catalysts result in aldolization (and crotonization) only acidic alkoxides produce simple esters only. Amphoteric or complex alkoxides, however, may combine both reactions and produce a glycol ester. 

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