Chemically modified oximato complexes of titanium(IV) isopropoxide as new precursors for the sol-gel preparation of nano-sized titania: crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂]

Abstract

Reactions of [Ti(OPrⁱ)₄] with various oximes, in anhydrous refluxing benzene yielded [Ti{OPrⁱ}_4-n{L}_n], where, n = 1-4 and LH = (CH₃)₂C=NOH (1-4), C₉H₁₆C=NOH (5-8) and C₉H₁₈C=NOH. The compounds were characterized by elemental analyses, molecular weight measurements, FAB-mass, FTIR and NMR (¹H, ¹³C{¹H}) spectral studies. The FAB-mass spectra of mono- (1), and di- (2), (6), (10) substituted products indicate their dimeric nature and that of tri- (3) and tetra- (4), (8) substituted derivatives suggest their monomeric nature. Crystal and molecular structure of [Ti{ONC₁₀H₁₆}₄·2CH₂Cl₂] (8A) suggests that the oximato ligands bind the metal in a dihapto η²-(N, O) manner, giving an eight coordinated species. Thermogravimetric curves of (3), (6) and (10) exhibit multi-step decompn. with the formation of TiO₂ as the final product in each case, at 900°C. Low temperature (~600°) sol-gel transformations of (2), (3), (4), (6), (7) and (8) yielded nano-sized titania (a), (b), (c), (d), (e) and (f), respectively. Formation of anatase phase in all the titania samples was confirmed by powder XRD patterns, FT-IR and Raman spectroscopy. SEM images of (a), (b), (c), (d), (e) and (f) exhibit formation of nano-grains with agglomer like surface morphologies. Compositions of all the titania samples were investigated by EDX analyses. The absorption spectra of the two representative samples, (a) and (f) indicate an energy band gap of 3.17 eV and 3.75 eV, respectively.