Carboxylic acid (HORc)-modified Ti(OR)4 products were used to study the effect that similarly
ligated species with substantially varied structures have on the final densification of the resultant ceramic
(in this case TiO2). The 1:1 stoichiometric products isolated from the reactions of [Ti(μ-ONep)(ONep)3]2 (1,
ONep = OCH2CMe3) and a variety of sterically hindered carboxylic acids [HORc: HOFc (HO2CH), HOAc
(HO2CCH3), HOPc (HO2CCHMe2), HOBc (HO2CCMe3), or HONc (HO2CCH2CMe3)] were identified by single-crystal X-ray diffraction and solid-state 13C MAS NMR spectroscopy as Ti3(μ3-O)(OFc)2(ONep)8 (2), Ti3(μ3-O)(OAc)2(ONep)8 (3), Ti6(μ3-O)6(OPc)6(ONep)6 (4), Ti2(μ-OBc)2(ONep)6 (5), and Ti3(μ3-O)(ONc)2(ONep)8
(6). Compounds 2, 3, and 6 adopt a triangular arrangement of Ti atoms linked by a μ3-oxide moiety with ORc
and ONep ligands supporting the basic framework. Compound 4 adopts a distorted, hexagon-prism geometry
of two offset [Ti−O−]3 rings with each six-coordinated metal possessing a terminal ONep and two monodentate
OPc ligands. The unique, nonesterified product 5 is dimeric with two μ-ONep, two unidentate bridging OBc,
and two terminal ONep ligands. The solution behaviors of 2−6 were investigated by NMR experiments and
were found to retain the solid-state structure in solution with a great deal of ligand rearrangement. Films of
TiO2 were made from redissolved crystals of 2−6. The highest density TiO2 thin films were derived from the
partially hydrolyzed, trinuclear, low-carbon-containing ONep complexes 2 and 3, as determined from
ellipsometric data.
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