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)1

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 TiO 2 ). The 1:1 stoichiometric products isolated from the reactions of [Ti(μ-ONep)(ONep) 3 ] 2 ( 1, ONep = OCH 2 CMe 3 ) and a variety of sterically hindered carboxylic acids [HORc: HOFc (HO 2 CH), HOAc (HO 2 CCH 3 ), HOPc (HO 2 CCHMe 2 ), HOBc (HO 2 CCMe 3 ), or HONc (HO 2 CCH 2 CMe 3 )] were identified by single-crystal X-ray diffraction and solid-state 13 C MAS NMR spectroscopy as Ti 3 (μ 3 -O)(OFc) 2 (ONep) 8 ( 2 ), Ti 3 (μ 3 -O)(OAc) 2 (ONep) 8 ( 3 ), Ti 6 (μ 3 -O) 6 (OPc) 6 (ONep) 6 ( 4 ), Ti 2 (μ-OBc) 2 (ONep) 6 ( 5 ), and Ti 3 (μ 3 -O)(ONc) 2 (ONep) 8 ( 6 ). Compounds 2, 3, and 6 adopt a triangular arrangement of Ti atoms linked by a μ 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 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 TiO 2 were made from redissolved crystals of 2 − 6 . The highest density TiO 2 thin films were derived from the partially hydrolyzed, trinuclear, low-carbon-containing ONep complexes 2 and 3, as determined from ellipsometric data.