Niobium alkoxide

The sol-gel method of preparing lithium niobate used lithium and niobium alkoxides. Alkoxides are often used in CVD methods, but unfortunately for the preparation of lithium niobate, lithium alkoxides are much less volatile than niobium alkoxides and to get the two metals deposited together it is better to use compounds of similar volatility. One way around this problem is to use a more volatile compound of lithium. One reported synthesis uses a p diketonate of lithium in which lithium is coordinated to 2,2,6,6-tetramethylheptan-3,5-dione (Me3CCOCH2COCMe3) (Figure 3.11). 

As a general observation, it is important to note that reaction between alkoxides and other metal derivatives, such as acetates, can be strongly dependent on the solvent and/or the addition order of the reactants [84]. Thus, no reaction is observed between anhydrous Pb(OAc)2 and Nb(OEt)s in THE at room temperature, but the acetate dissolves readily in toluene at room temperature in the presence of the niobium alkoxide with formation of a Pb-Nb species [80]. Another general feature is that in heterometallic acetatoalkoxides obtained by this route, the metal introduced as an alkoxide appears predominant. More condensed species are obtained if the reaction is achieved at higher temperatures [93] ... 

The niobium alkoxides are dimeric species, and they need to dissociate into the monomeric species before CO2 can react. Such reaction depends on the solvent used alcohols favor the dissociation more than benzene. This is because of the capacity of alcohols to assist the Nb-O bond cleavage in the dimer by coordinating to Nb. However, alcohols can bind to the coordinatively unsaturated monomeric Nb-alcoxo species formed upon dissociation, preventing their re-association. Such... 

The bismuth aUcoxide was insoluble in methoxyethanol because of its own strong association however, it easily dissolved in methoxyethanol containing strontium alkoxide in Sr(OR)2 Bi(OR)3 molar ratios of >0.5 (Katayama and Sekine, 1991). As previously reported, the strong association of the bismuth alkoxide can be destroyed by the formation of a strontium-bismuth double alkoxide. The formation of the strontium-bismuth double alkoxide is discussed next. Also, the bismuth alkoxide was insoluble in strontium-tantalum or strontium-niobium double alkoxide solutions. The strontium-bismuth double alkoxide formed and then reacted with the tantalum or niobium alkoxide to prepare uniform alkoxide complex solutions (Kato et al., 1998). 

The broadening behavior of the signal for niobium alkoxides, with ligand substitu-... 

Ammonia and alcohol may be used instead of sodium alkoxides to manufacture alkoxides of titanium and other metals such as tirconium, hafnium, germanium, niobium, tantalum, aluminum, and tin. 

Niobium Products Co., 50 m /g). Many different synthesis methods have been used to prepare supported metal oxide catalysts. In the case of supported vanadium oxide catalysts, the catalysts were prepared by vapor phase grafting with VOCI3, nonaqueous impregnation (vanadium alkoxides), aqueous impregnation (vanadium oxalate), as well as spontaneous dispersion with crystalline V2O5 [4]. No drastic reduction of surface area of the catalysts was observed. 

Lithium niobate is a ferroelectric material used as an optical switch. Preparation by the simple ceramic method leads to problems in obtaining the correct stoichiometry, and a mixture of phases often results. Several sol-gel preparations have been described, their advantage being the lower temperature required for the preparation and the greater homogeneity of the product. One such preparation starts with lithium ethoxide (LiOC2H5 (or LiOEt)) and niobium ethoxide Nb2(OEt)io. Each ethoxide was dissolved in absolute ethanol and the two solutions mixed. The addition of water leads to partial hydrolysis giving hydroxy-alkoxides, for example ... 

Peercy, P.S., Dosch, R.G., and Morosin, B., "Preparation and Structural Studies of the Hydrolysis Products of Titanium, Niobium and Zirconium Alkoxides," SAND76-O556, Sandia Laboratories, Albuquerque, NM (1976). 

Vinyl ethers have also been prepared by addition of alkoxides to acetylene,6 7 6 elimination from halo ethers and related precursors,6 8 and vinyl exchange reactions.6 Reaction of an electrophilic tungsten carbenoid with methylene phosphorane or diazomethane also produces vinyl ethers.9 Enol ethers have resulted from the reaction of some tantalum and niobium carbenoids with esters,10 and the reaction of phosphoranes with electrophilic esters.4... 

The derivatives in the lower oxidation states Nb(II), Nb(HI), Ta(III) (known mainly for niobium) were obtained by the reduction of M(OR)5 by sodium amalgam [404, 1187], and bimetallic methoxoniobates (IV) by reduction with hydrogen in statu nascendi (Mg + MeOH) or on cathodic reduction in solution (method 7). The alkoxide chlorides ofNb(HI) and Nb(IV) crystallize on alcoholysis ofthe corresponding chlorides at low temperatures (method4) [416, 1731],... 

The phenoxides of Nb(II) and alkoxides of Ta(III), as well as the corresponding derivatives of vanadium should be stabilized by the sterically hindered ligands. The alkoxide chlorides of niobium (Eft) and (TV) are diamagnet-... 

The numerous alkoxide halides of niobium and tantalum containing the atoms of all the known halogenes from F to I and a broad range of radicals are considered in the Table 12.17. 

In addition to the bimetallic complexes of rhenium and alkaline metals formed as byproducts in the exchange reactions of rhenium halids with alkali alkoxides (such as, for example, LiReO(OPr )5 xLiCl(THF)2 [519]) there has been recently prepared a number ofbimetallic complexes ofrhenium and molybdenum, rhenium and tungsten, and rhenium and niobium [904, 1451]. The latter are formed either due to the formation of a metal-metal bond, arising due to combination of a free electron pair on rhenium (V) and a vacant orbital of molybdenum (VI) atom or via insertion of molybdenum or tungsten atoms into the molecular structure characteristic of rhenium (V and VI) oxoalkox-ides. The formation of the compounds with variable composition becomes possible in the latter case. 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

A new series of niobium derivatives (62) of the IV-phenylurethanes has been obtained586 from the insertion reaction between niobium penta-alkoxides and phenyl isocyanate. Most of the products are yellow liquids, one is white and the rest are brown or black solids or semi-solids. They exhibit v(C=0) in the range 1690— 1730 cm-1. Insertion of up to three molecules of phenyl isocyanate occurs readily at... 

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