Part I. Chemical processing of barium titanates. Part II. The chemistry of sulfotitanic acids, molecular analogues of sulfated metal oxide superacids
Liang, Shurong
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Permalink
https://hdl.handle.net/2142/23170
Description
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
Issue Date
1996
Doctoral Committee Chair(s)
Klemperer, Walter G.
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Inorganic
Engineering, Materials Science
Language
eng
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.
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