Implications for the thin-film densification of TiO2 from carboxylic acid-modified titanium alkoxides.: Syntheses, characterizations, X-ray structures of Ti3(μ3-O)(O2CH)2(ONep)8, Ti3(μ3-O)(O2CMe)2(ONep)8, Ti6(μ3-O)6(O2CCHMe2)6(ONep)6, [Ti(μ-O2CCMe3)(ONep)3]2, and Ti3(μ3-O)(O2CCH2CMe3)2(ONep)8 (ONep = OCH2CMe3)

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(mu-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 C-13 MAS NMR spectroscopy as Ti-3(mu(3)-O)(OFc)(2)(ONep)(8) (2), Ti-3(mu(3)-O)(OAc)(2)(ONep)(8) (3), Ti-6(mu(3)-O)(6)(OPc)(6)(ONep)(6) (4), Ti-2(mu-OBC)(2)(ONep)(6) (5), and Ti-3(mu(3)-O)(ONc)(2)(ONep)(8) (6). Compounds 2, 3, and 6 adopt a triangular arrangement of Ti atoms linked by a mu(3)-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 mu-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.