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

• Published in: Molecules (Basel, Switzerland) Switzerland), 2021-09, Vol.26 (18), p.5588
• Main Authors: Passadis, Stamatis S, Hadjithoma, Sofia, Siafarika, Panagiota, Kalampounias, Angelos G, Keramidas, Anastasios D, Miras, Haralampos N, Kabanos, Themistoklis A
• Format: Article
• Language: English
• Subjects: band gap modification; Blue shift; Crystal structure; Density functional theory; ESI-MS studies; Infrared spectroscopy; Lability; Ligands; Luminescence; Magnetic resonance spectroscopy; Metals; Molecular orbitals; multinuclear NMR; NMR; NMR spectroscopy; Nuclear magnetic resonance; photoluminescence; Physical sciences; Single crystals; Solid state; Spectra; Structural analysis; Structural models; Titanium; titanium(IV) oxo-clusters; Wavelengths
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules26185588

The siderophore organic ligand ,2-dihydroxybenzamide (H dihybe) 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 H dihybe with TiCl in methyl alcohol and KOH yielded the tetranuclear titanium oxo-cluster (TOC) [Ti (μ-O) (HOCH ) ( -Hdihybe) (Hdihybe) ]Cl ∙10H O∙12CH OH ( ). 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 H dihybe 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 H dihybe. 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 (CD OD) studies of reveal that it retains its integrity in CD OD. The observed NMR changes upon addition of base to a CD OD 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.