Isolation of a mixed niobium tantalum alkoxide

Abstract

i_5 0 A . I O h y d r o l y s e d Figure 1. Esterification of chrysotlle-asbestos by allyl alcohol: the units on the ordinate are expressed in milliequivalents of ester groups/100 g of inorganic substrate; degree of hydrolysis reported on the abscissa represents the fraction (5%) of the original magnesium which was eliminated; curve A, hydrolyzed fiber; curve B, chlorinated fiber.out the esterification. The procedure of chlorination is described in detail elsewhere." This reaction substitutes S i c 1 groups for the silanol groups generated by hydrolysis. Results and DiscussionThe results obtained in this study are summarized in Table I1 and in Figure 1. One can see that the degree of esterification increases gradually with the degree of hydrolysis. This result clearly shows that esterification is only possible on the siloxanic surface. One also notices that the degree of coverage is relatively constant and does not depend on the degree of hydrolysis of the fiber. The mean degree of coverage is 316 O R groups/nm2 for the hydrolyzed fibers and 400 OR groups/nmz for the chlorinated ones. This result represents a relative increase of about 26%. This increase in the degree of surface coverage could result from the higher reactivity of the S i 4 groups as compared with that of the silanol groups. If we compare our results with the figure obtained by NotesNotes W a r t m a d for the esterification of silica gel chloride with short chain alcohols, we see that the degree of coverage obtained here is much higher. For example, for the esterification of I-propanol, Wartmann grafted 168 QR/100 nm2. It is our opinion that the higher degree of coverage obtained with chrysotile results from the very regular quasicrystalline structure of the surface produced by hydrolysis compared with the mainly amorphous surface of synthetic silica gel. Iler7 has calculated on a theoretical basis that there are between 800 and 900 OH groups/100 nm* of a silanolic surface. If we take into consideration the problem of steric hindrance introduced by the allylic ester groups, we may expect a maximum degree of substitution of 50%, Le. between 400 and 500 OR groups/ 100 nm2. The experimental values that we have obtained in this study are very close to this theoretical value, especially for the chlorinated fibers.In conclusion, in this study, it has been shown that the reaction of esterification of hydrolyzed or chlorinated chrysotile is possible with an efficiency higher than that obtained for silica gel. This method is very convenient for grafting a continuous layer of organophilic groups onto the surface of phyllosilicates.Acknowledgment. The authors wish to thank Professor J. J. Fripiat, Dr. M. della Faille, and Mr. M. Van Russelt for helpful discussion, They are also indebted to the Institut pour 1'Encouragement a la Recherche Scientifique dans 1'Industrie et 1'Agriculture (I.R.S.I.A.) and to the S. A. Eternit for financial support.Dimeric niobium and tantalum alkoxides have been known for a long time1 and have been the subject of many studies2...

Termocromismo em soluções de alcóxidos de Vanádio(IV): uma abordagem pela modelagem molecular

“…1 Este uso pode ser explicado pela facilidade com que óxidos de alta pureza e de estequiometria e estrutura definidas podem ser obtidos a partir destes alcóxidos, principalmente através do processo sol-gel ou pelos métodos de deposição química ou física de vapor (CVD e PVD). 1,2 As características dos produtos advindos destes processos são amplamente dependentes das estruturas moleculares dos precursores em solução.…”

“…5 Recentemente, utilizando uma outra rota sinté-tica, [V 2 (μ-OPr i ) 2 (OPr i ) 6 ] foi obtido em forma de monocristais, 6 que, dissolvidos em tolueno ou hexano, apresentaram um comportamento termocrômico marcante, com colorações que variavam do amareloouro (abaixo de 210 K) ao azul-cobalto (a partir de 315 K), passando pelo verde nas temperaturas intermediárias. 7 Um comportamento termocrômico semelhante foi observado para um outro alcóxido de vanádio(IV), o [V 2 (μ-ONep) 2 6 ]. 8 Entretanto, em especial no sistema com neopentóxido, não há evidências espectroscópicas inequívocas sobre a natureza das espécies moleculares que mudam a composição do sistema em resposta à variação da temperatura.…”

“…Este trabalho propôs-se a sugerir a natureza das espécies quí-micas responsáveis pelo comportamento termocrômico tão incisivo destes alcóxidos de vanádio(IV), [V 2 (μ-OR) 2 6 ] foram obtidos em rendimentos de 40 e 60%, respectivamente, por uma rota sintética simples e reprodutível. 8 Os espectros de absorção na região do infravermelho (400 a 4000 cm -1 ) com transformada de Fourier (IV-TF) foram obtidos em um instrumento BIO-RAD, Excalibur Series (FTS 3500 GX).…”

Crystal structure of tetraethylammonium hexachloridotantalate(V), C8H20Cl6NTa

“…TaCl5) are readily oxidized. The oxidized Ta(V) reagent is very unreactive and seemingly not very useful in coordination chemistry [6]. Attempts have been made to create synthons that are less readily oxidized and much more durable in atmospheric conditions.…”

Synthesis of Derivatives of Organoheterotrimetallic dibutyl-[Al(III), Sn(IV), Ti(IV)]- μ -oxoisopropoxide- μ-oxo n-Propoxide with Salicylates

“…The crystal structures range from simple rock salt to highly complex incommensurately modulated structures and the nature of the metal-oxygen bonding varies from nearly ionic to covalent or metallic 1,2 . Multimetallic oxides cover an always wider range of applications in electronics, optics [3][4][5] , magnetism [6][7][8] , catalysis 9 and environmental issues 10 . High-tech applications rely on materials in high purity and/or in a variety of shapes, formulations or microstructures (nano-particles, coatings, porous matrices, etc.)…”