Synthesis, Structural and Physicochemical Characterization of a Titanium(IV) Compound with the Hydroxamate Ligand ,2-Dihydroxybenzamide

The siderophore organic ligand ,2-dihydroxybenzamide (Hdihybe) incorporates the hydroxamate group, in addition to the phenoxy group in the ortho-position and reveals a very rich coordination chemistry with potential applications in medicine, materials, and physical sciences. The reaction of Hdihybe with TiCl in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [Ti(μ-O)(HOCH)(-Hdihybe)(Hdihybe)]Cl∙10HO∙12CHOH (). The titanium compound was characterized by single-crystal X-ray structure analysis, ESI-MS, C, and H NMR spectroscopy, solid-state and solution UV-Vis, IR vibrational, and luminescence spectroscopies and molecular orbital calculations. The inorganic core Ti(-O) of constitutes a rare structural motif for discrete Ti oxo-clusters. High-resolution ESI-MS studies of in methyl alcohol revealed the presence of isotopic distribution patterns which can be attributed to the tetranuclear clusters containing the inorganic core {Ti(-O)}. Solid-state IR spectroscopy of showed the presence of an intense band at ~800 cm which is absent in the spectrum of the Hdihybe and was attributed to the high-energy ν(Ti--O) stretching mode. The (C=O) in is red-shifted by ~10 cm, while the (N-O) is blue-shifted by ~20 cm in comparison to Hdihybe. Density Functional Theory (DFT) calculations reveal that in the experimental and theoretically predicted IR absorbance spectra of the ligand and Ti-complex, the main bands observed in the experimental spectra are also present in the calculated spectra supporting the proposed structural model. H and C NMR solution (CDOD) studies of reveal that it retains its integrity in CDOD. The observed NMR changes upon addition of base to a CDOD solution of , are due to an acid-base equilibrium and not a change in the Ti coordination environment while the decrease in the complex's lability is due to the improved electron-donating properties which arise from the ligand deprotonation. Luminescence spectroscopic studies of in solution reveal a dual narrow luminescence at different excitation wavelengths. The TOC exhibits a band-gap of 1.98 eV which renders it a promising candidate for photocatalytic investigations.