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Title:Part I. Chemical processing of barium titanates. Part II. The chemistry of sulfotitanic acids, molecular analogues of sulfated metal oxide superacids
Author(s):Liang, Shurong
Doctoral Committee Chair(s):Klemperer, Walter G.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemistry, Inorganic
Engineering, Materials Science
Abstract:Part I. Several new barium titanium alkoxides, $\rm BaTi(OPh)\sb6\cdot2DMF$ (BTP), (Ba(HOCH$\sb2$-CH$\rm\sb2OH)\sb4(H\sb2O)\rbrack\lbrack Ti(OCH\sb2CH\sb2O)\sb3\rbrack (BTG),\ BaTi\sb2)O(OBz)\sb8\cdot$BzOH (Bz = benzyl) and $\rm BaTi\sb4(OR)\sb{18}\ (R = Et,\ \sp{n}Pr),$ have been synthesized and structurally characterized. The BTP complex, as a single-source precursor, is well-suited for the sol-gel processing of BaTiO$\sb3$ in the form of gels, powders, and thin films. The BTG complex is a viable precursor for the processing of BaTiO$\sb3$ powders by thermal decomposition. Calcination of BTG at 600$\sp\circ$C yields submicron BaTiO$\sb3$ powders, which can be sintered into BaTiO$\sb3$ ceramics at 1300$\sp\circ$C. Gels and xerogels have been prepared from the complexes $\rm BaTi\sb2O(OBz)\sb8\cdot$BzOH and $\rm BaTi\sb4(OEt)\sb{18}.$ Heat treatment of the xerogels derived from $\rm BaTi\sb2O(OBz)\sb8\cdot$BzOH at 1100$\sp\circ$C yields $\rm BaTi\sb2O\sb5$ and a small amount of $\rm BaTiO\sb3.$ Phase pure BaTi$\rm 4O\sb9$ is obtained after firing the xerogels prepared from $\rm BaTi\sb4(OEt)\sb{18}$ at temperatures above 1200$\sp\circ$C.
Part II. The sulfotitanic acids $\rm H\sb2\lbrack Ti\sb6O\sb4(SO\sb4)\sb4(OR)\sb{10}\rbrack\ (R = Et, Pr\sp{n}),$ the first titanium heteropolyacids, are prepared by reaction of Ti(OR)$\sb4$ with aqueous sulfuric acid in alcohol solution. Their conjugate bases, $\rm (Et\sb3NH)\sb2\lbrack Ti\sb6O\sb4(SO\sb4)\sb4(OR)\sb{10}\rbrack,$ are obtained by reaction of the acids with Et$\sb3$N. According to single crystal X-ray diffraction studies of the ethoxide acid $\rm H\sb2\lbrack Ti\sb6O\sb4(SO\sb4)\sb4(OEt)\sb{10}\rbrack$ and its triethylamine salt $\rm (Et\sb3NH)\sb2\lbrack Ti\sb6O\sb4(SO\sb4)\sb4(OEt)\sb{10}\rbrack,$ both compounds have the same anion structure containing tridentate sulfate ligands, each bonded to three Ti(IV) centers. The proton in the ethoxide acid is bonded to a terminal ethoxide oxygen. The sulfate stretching vibrations in the ethoxide acid have been identified by infrared spectroscopy using $\sp{18}$O-labeled sulfate. Comparison of these sulfate vibrational spectra with data reported for sulfated titania reveals several common features, implicating tridentate sulfate coordination in sulfated titania. Accordingly, a structural model is proposed for sulfated titania in which sulfate ions adopt a tridentate coordination mode, five-coordinate Ti(IV) centers are the Lewis acid sites, and water molecules coordinated to the Ti(IV) centers are the Bronsted acid sites.
Issue Date:1996
Rights Information:Copyright 1996 Liang, Shurong
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9702583
OCLC Identifier:(UMI)AAI9702583

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