Crystalline bis(η⁵-cyclopentadienyl)bis(benzoato/carboxylato)titanium(IV) precursor-directed route to functional titanium dioxide nanomaterials

Five titanocene(IV) carboxylates of the general formula Cp₂Ti(O₂CR)₂ viz., [Ti(η⁵-C₅H₅)₂(O₂CC₆H₅-4-CH₃)₂] (1), [Ti(η⁵-C₅H₅)₂(O₂CC₄H₃-2-O)₂] (2), [Ti(η⁵-C₅H₅)₂(O₂CC₄H₃-3-O)₂] (3), [Ti(η⁵-C₅H₅)₂(O₂CC(CH₃)₃)₂] (4), and [Ti(η⁵-C₅H₅)₂(O₂C(CH)C(CH₃)₃)₂] (5) have been synthesized. All the titanocene(IV) carboxylates have been characterized by IR, ¹H, and ¹³C NMR spectroscopic techniques, and the crystal and molecular structures of 1–5 have been determined by single crystal X-ray crystallography. The structures present similar features with monodentate carboxylate ligands and tetrahedral Ti centers, assuming that each cyclopentadienyl (Cp) ring occupies one position only. The differences in the structures relate primarily to the relative orientations of the carboxylate ligands. In the molecular packing, non-conventional Cp-C–H···O(carbonyl) hydrogen bonds are observed in each case and lead to supramolecular chains in each of 1, 4, and 5. In 2, the 2-furyl-O atoms also participate in C–H···O interactions leading to a two-dimensional array. Finally, in 3, a two-dimensional array arises as a result of Cp-C–H···O(carbonyl) and 3-furyl-C–H···O(carbonyl) interactions. As representative example, 3 was used as starting material for the synthesis of TiO₂ nanoparticles (NPs). An effective and simple wet-chemical method involving calcination and ultrasonication is suggested for obtaining pure anatase TiO₂ NPs, which were confirmed from the powder XRD and imaging techniques such as SEM, TEM, and EDS.