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Title: Molecular precursors for the preparation of homogenous zirconia-silica materials by hydrolytic sol-gel process in organic media. Crystal structures of [Zr{OSi((OBu)-Bu-t)(3)}(4)(H2O)(2)]center dot 2H(2)O and [Ti((OBu)-Bu-t){OSi((OBu)-Bu-t)(3)}(3)]
Authors: DHAYAL, V
Issue Date: 2012
Citation: DALTON TRANSACTIONS, 41(31)9439-9450
Abstract: Zr(OPri)(4)center dot(PrOH)-O-i] reacts with [HOSi((OBu)-Bu-t)(3)] in anhydrous benzene in 1 : 1 and 1 : 2 molar ratios to afford alkoxy zirconosiloxane precursors of the types [Zr(OPri)(3){OSi((OBu)-Bu-t)(3)}] (A) and [Zr(OPri)(2){OSi-((OBu)-Bu-t)(3)}(2)] (B), respectively. Further reactions of A or B with glycols in 1 : 1 molar ratio afforded six chemically modified precursors of the types [Zr(OPri)(OGO){OSi((OBu)-Bu-t)(3)}] (1A-3A) and [Zr(OGO)-{OSi((OBu)-Bu-t)(3)}(2)] (1B-3B), respectively [where G = (-CH2-)(2) (1A, 1B); (-CH2-)(3) (2A, 2B) and (-CH2CH2CH(CH3-)} (3A, 3B)]. The precursors A and B are viscous liquids, which solidify on ageing whereas the other products are all solids, soluble in common organic solvents. These were characterized by elemental analyses, molecular weight measurements, FAB mass, FTIR, H-1, C-13 and Si-29-NMR studies. Cryoscopic molecular weight measurements of all the products, as well as the FAB mass studies of 3A and 3B, indicate their monomeric nature. However, FAB mass spectrum of the solidified B suggests that it exists in dimeric form. Single crystal structure analysis of [Zr{OSi((OBu)-Bu-t)(3)}(4)(H2O)(2)]center dot 2H(2)O (3b) (R-fac = 11.9%) as well as that of corresponding better quality crystals of [Ti((OBu)-Bu-t){OSi((OBu)-Bu-t)(3)}(3)] (4) (R-fac = 5.97%) indicate the presence of a M-O-Si bond. TG analyses of 3A, B, and 3B indicate the formation of zirconia-silica materials of the type ZrO2 center dot SiO2 from 3A and ZrO2 center dot 2SiO(2) from B or 3B at low decomposition temperatures (<= 200 degrees C). The desired homogenous nano-sized zirconia-silica materials [ZrO2 center dot nSiO(2)] have been obtained easily from the precursors A and B as well as from the glycol modified precursors 3A and 3B by hydrolytic sol-gel process in organic media without using any acid or base catalyst, and these were characterized by powder XRD patterns, SEM images, EDX analyses and IR spectroscopy.
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